Geometrical DYALLING or, Dyalling by a line of CHORDS only by John COLLINS accountant Philomath London Printed for Francis Cossinet in Tower Street and for H: Sutton behind exchange General Scheme Projection of the Sphere Anno 1659. In a Circle In a Parralellogram Chords fitted to the Schemes in the book ruler Chords in time fitted to the book ruler geometrical Dyalling: OR, DYALLING Performed by a Line of CHORDS only, Or by the PLAIN SCALE. Wherein is contained two several Methods of Inscribing the Hour-Lines in all Plains, with the Substile, style and Meridian, in their proper Coasts and Quantities; Being a full Explication and Demonstration of divers difficulties in the Works of Learned Mr. Samuel Foster deceased, late Professor of Astronomy in Gresham college,; Also a Collection of divers things from the Works of Clavius and others. Whereto is added four new Methods of Calculation, for finding the Requisites in all Leaning Plains, with full directions suited to each Method for placing them in their proper Coasts, without the help of any Dclinations. Also how by Projecting the Sphere, to measure off all the Arks found by Calculation, and to determine what hours are proper to all kind of Plains, omitting superfluity. Lastly, the making of dials from three Shadows of a Gnomon placed in a Wall at random, with a Method of Calculation suited thereto, and divers ways from three Shadows, to find a Meridian-line. Written by John Collins of London accountant, Philomath. London, Printed by Thomas Johnson for Francis Cossinet, and are to be sold at his Shop at the Anchor and Mariner in Tower-street, at the end of Mincing-lane, with other Mathematical Books; Also to be sold by Henry Sutton Mathematical Instrument-Maker, living in Threed-needle Street behind the Exchange. 1659. To the Reader. BEing in conference with my loving friend Mr. Thomas Rice, one of the Gunners of the Tower, much exercised in making of dials in many eminent places of the City, he was pleased to communicate unto me the knowledge of a General Scheme, for Inscribing the Requisites in all Oblique Leaning Plains, which he added, was the useful Invention of the Learned Master Samuel Foster, Professor of Astronomy in Gresham college London, deceased, from whom he received Instructions concerning the same, in the year 1640. And the said Mr. Rice not having his Papers about him, did dictate to me from his Memory the Construction and Practice of the said Scheme, which I afterwards methodised just as it is delivered in page 25 and 26. At the same time also I received directions for Inscribing the Substile and style in upright Decliners, and East or West Reclining, or Inclining Plains, but they were of another man's Invention, and did not seem to be derived from the former general Scheme, and therefore I have not used them in this Treatise, but derived the performance thereof from the said general Scheme: Moreover, Mr. Rice added, that in regard of the death of the Author, and since of his Executor, who had the care and inspection of his Papers, I should do well to Study out the Demonstration of the former Scheme, and make it public, the rather, because it hath been neglected. The manner of Inscribing the hour-lines being already published in a Treatise of the Authors, entitled, Posthumi Posteri; this desire of his, which was also furthered by Mr. Sutton and others, I am confident is fully effected in the following Treatise, and much more than was in his Request, and here let me add, that I have had no other light from the endeavours of the Learned Author, than what was as above communicated unto me, all which might be expressed in half a page of paper, or little more, to which I have made this large Access and Collection, nam facile est inventis adore; not that I would hereby any thing endeavour to eclipse the author's Work, the excellency of whose Inventions in this and other kinds, will speak forth his Renown to all posterity. And though in probability I have not performed so much, nor so well, as was obvious to the knowledge of the Learned Author, yet I am confident when the Reader understands what is written, he would be as loath to be without the knowledge thereof, as myself; and I am induced to believe, that the Author left nothing written about many particulars in this Treatise; throughout which, we suppose the Reader, furnished with the common Rudiments of Geometry, that he can raise Perpendiculars, draw Parallels, describe a Parralellogram, bring three points into a Circle, understands Definitions and terms of Art, knows what a Line of Chords is, can prick off an Arch thereby; all which, with Delineations for all the usual Cases of Triangles, both from Projection and Proportions, the Reader will meet with in my Treatise, called, The Mariners Plain Scale new plained, now in the Press. Vale & fruere. I remain thy friend, and a Well-willer to the public Advancement of Knowledge, JOHN COLLINS. The Contents: Dials distinguished Page 1, 2 To take the sun's Altitude without Instrument p. 3 To find the Reclination of a Plain p. 4 Also the Declination thereof p. 5 A general proportion and scheme for finding the sun's Azimuth or true Coast p. 6 To draw a Horizontal dial p. 7 Also a South dial p. 8 A new way to divide a Tangent live into five hours and their quarters p. 10, 11 A direct South Polar dial p. 12 To prick off the Requisites of upright Decliners p. 13 To prick off an Arch or Angle by Sines or Tangents p. 14 The scheme for placing the Requisites of upright Decliners demonstrated p. 15, 16 To inscribe the hour-lines in an upright Decliner p. 17 The Demonstration thereof p. 18 to 21 An East dial p. 22 Requisites placed in East or West leaning Plains p. 23 The Demonstration thereof p. 25 The Construction of the general scheme for placing the Requisites in Declining Re-Inclining Plains p. 25 to 27 The first Method of Calculation for Oblique Plains p. 28 to 30 And directions for the true placing the Requisites suited thereto p. 30, 31 The general scheme demonstrated p. 32 to 34 The hour-lines inscribed in an Oblique Plain ibid. The general scheme fitted for Latitudes under forty five degrees p. 35 To draw the hour-lines in a Declining Polar Plain p. 36 Also how to delineate the hour-lines in Plains having small height of style p. 37, 38 Another way to perform the same p. 39 to 41 A second Method of Calculation for Oblique Plains p. 42 Proportions for upright Decliners p. 43 A third Method of Calculation for Oblique Plains p. 44 Directions for placing the Requisites suited thereto p. 46 A fourth Method of Calculation for Oblique Plains p. 47 Through any two points assigned within a Circle to draw an Arch of a Circle that shall divide the primitive Circle into two Semicircles. p. 49 To measure the Arks of upright Decliners by Projection p. 50 Also the Arks of leaning East or West Plains thereby p. 51 To project the Sphere for Oblique Plains— To measure off all the Arks that can be found by Calculation With the Demonstration of all the former Proportions— from p. 52 to 59 To determine what Hours are proper to all Plains p. 60 to 61 Another Method of inscribing the Hour-lines in all Plains by a Parallelogram p. 62 To draw the Tangent Scheme suited thereto p. 63. The Hour-lines so inscribed in a Horizontal and South dial p. 63, 64 As also in an upright Decliner p. 65 With another Tangent Scheme suited thereto for pricking them down without the use of Compasses p. 66, 67 A general Method without proportional work, for fitting the Parallelogram into Oblique Plains that have the Requisites first placed p. 69, 70 By help of three shadows to find a Meridian-line p. 70, 71 Another Scheme suited to that purpose p. 73 A Method of Calculation for finding the Azimuth, Latitude, Amplitude, &c. by three shadows p. 75 From three shadows to inscribe the Requisites and Hour-lines in any Plain p. 77 Which is to be performed by Calculation also p. 97 Characters used in this Book. + Plus, for more, or Addition.- Minus less, or Substraction.= Equal. q For square. □ Square. ▭ The Rectangle or Product of two terms. ∷ for Proportion. If the Brass Prints in this Book be thought troublesome to bind up, they may be placed at the end thereof, for the Pages to which they relate, are graved upon them. A Quadrant of a Circle being divided into 90d, all that is required in this Treatise, is to prick off any number of the said degrees with their subdivisions, which may be easily done anywhere from a Quadrant drawn and divided into nine equal Parts, and one of those parts into ten subdivisions, called degrees, but for readiness the equal divisions of a whole. Quadrant are transferred into a right line (as in the Frontispiece) called a Line of Chords, serving more expeditely to prick off any number of degrees or minutes in the Arch of a Circle. An Advertisement. The Reader may possibly desire to be furnished with such Scales to any Radius, these and all manner of other Mathematical Instruments either for Sea or Land, are exactly made in Brass or Wood, by Heury Sutton in Threed-needle-street, behind the Exchange, or by William Sutton in Upper Shadwell, a little beyond the Church, Mathematical instrument-makers'. A direct South dial Reclining 60d Lat 51d 32′ An erect direct North dial at 51d 32′ A South dial Declin 40d East Reclining 60d Lat 51d 32′ A North dial Declin 40d West Reclining 75d Latitude 52d 32′ THE DISTINCTION OF dials. THough much of the subject of Dyalling hath been wrote already, by divers in diverse Languages, notwithstanding the Reader will meet with that in this following Treatise, which will abundantly satisfy his expectation, as to the particulars in the Preface, not yet divulged in any Treatise of this nature. In this Treatise, that we might not be too large, divers definitions are passed over, supposing that the Reader understands what a dial is, what hour Lines are, that that part of the style that shows the hour, aught to be in the Axis of the World, that the hour Lines being projected on any Regular Flat, will become straight Lines. Dial's are by Clavius in the second Chapter of his gnomonics distinguished into Seventeen kinds. 1. The Horizontal, being parallel to the Horizon. 2. South and North direct, by some called a Vertical dial, because parallel to the prime Vertical or Circle of East and West. 3. 4. South direct, Reclining or North Inclining less more Than the Pole. 5. 6. South direct, Inclining or North Reclining less more Than the Equinoctial 7. South direct Reclining, or North Inclining to the Pole, called a direct Polar Plain, because Parallel thereto 8. South direct Inclining, or North Reclining to the Equator, called an Equinoctial Plain, because parallel thereto. 9 South and North, Declining East or West. 10. East and West direct. 11. East and West direct, Reclining or Inclining. 12. A South North Plain declining East or West Reclining Inclining to the Pole, called a Polar Decliner. 13. A South North Plain Declining East or West Inclining Reclining to the Equinoctial, called an Equinoctial Decliner. 14. 15. A South North Plain Declining East or West Reclining Inclining Whereof are two sorts, the one passing above, the other beneath the Pole 16. 17. A. South North Plain Declining East or West Inclining Reclining whereof are 2. sorts, the one passing above the Equinoctial, the other beneath it. Of each of these we shall say something, but before we proceed, it will be necessary in the first place to show how to find the situation of any Plain. 1. To find whether a Plain be Level or Horizontal. The performance hereof is already showed by Mr. Stirrup, in his complete Dyallist, Page 58. where he hath a Scheme to this purpose, I shall only mention it: Get a smooth Board, let it have one right edge, and near to that edge, let a hole be cut in it for a Plummet to play in; draw a Line 'cross the Board Perpendicular, to the straight edge thereof passing through the former hole; if then setting the Board on its smooth edge, and holding it Perpendicularly, so that the Plummet may play in the hole, if which way soever the Board be turned, the thread will fall (being held upright with the Plummet at the end of it, playing in the former hole) directly on the Perpendicular Line drawn 'cross the Board, the said Line no ways Reclining from it, the Plain is Horizontal, otherwise not. 3. To take the Altitude of the Sun without Instrument. Upon any Smooth Board, draw two Lines at right Angles, as AB and AC, and upon A as a centre with 60d of a Line of Chords describe the Arch BC, and into the centre thereof, at A drive in a Pin or Steel Needle, upon which hang a thread and Plummet, than when you would observe an Altitude, hold the Board so to the Sun, that the shadow of the Pin or Needle may fall on the Line AC, and where the thread intersects the Arch BC, set a mark, suppose at E than measure the Ark BE on your Line of Chords, and it shows the Altitude sought, for want of a Line of Chords, you may first divide the Arch BC into 9 parts, and the first of those Divisions into 10 smaller parts. 3. To draw a Horizontal and Vertical Line upon a Plain. The readyest and most certainest way to do this, especially if the Plain lean downwards from the Zenith, will be by help of a thread and Plummet held steadily, to make two pricks at a competent distance in the shadow of the thread on the Plain, projected by the eye, and a Line drawn through those, or parallel to those two points, shall be the Plains perpendicular or Vertical Line, and a Line drawn perpendicular to the said Line, shall be the Plains Horizontal Line. To find the Reclination of a Plain. The Reclination of a Plain, is the Angle comprehended between the Plains perpendicular, and the Axis of the Horizon, and the same Definition may serve for the Inclination, only the upper face of a Plain, leaning from the Zenith, is said to recline, and the under face to incline. In this sense Mr. Oughtred in his Circles of Proportion, Mr. Wells in his Dyalling, Mr. Newton in his Institution, and Mr. Foster in his late writings, understand it, and so it is to be taken throughout this Treatise; but here it will not be amiss to intimate that Mr. Gunter, Mr. Wingate, and Mr. Foster in a Treatise of a Quadrant, published in Anno 1638. account the Inclination from the Horizon; the compliment of the Angle here defined, and accordingly have suited their Proportions thereto, in which sense, the Reclining side is said to be the upper face of an Incliner; but for the future it will be inconvenient to take it any more in that Acception. Now to find the Reclination of a Plain, apply the straight edge of the Board we used for trying of Horizontal Plains, to the Plains perpendicular, holding the thread and plummet so in the grooved hole, that it may intersect the line, parallel to the straight edge of the Board, and make two pricks upon the Board where the thread passeth, and it will make an Angle with the said Line, equal to the Plains Reclination, to be measured with Chords, according as was directed for taking of Altitudes; and if need require, a Line may be drawn parallel to that drawn on the Board, which represented the thread, which will make the same Angle with the Plains perpendicular, the former Line did. The Inclination will be easily got, by applying the straight edge of the Board, to the Plains perpendicular, and holding the thread and plummet so at liberty, as that it may cross the Line parallel to the board's straight edge, and it will make an Angle therewith, equal to the Plains Inclination. Of Declining Plains. A Plain hath its Denominations from the situation of its Poles: by the Poles of a Plain, is meant a Line imagined to pass through the Plain at right Angles thereto, the Extremities of which Line on both sides the Plain, are called its Poles. If a Plain look full South, without swerving, either to the East or West; it is said to be a direct South Plain, if it swerve towards East or West, it is said to decline thereto; if it stand upright without leaning, it is said to be erect Now a South Plain that declines Eastward, the opposite face thereto, is said to be a North Plain declining as much Westward, by which means the Declination of a Plain will never exceed 90d, and to which sense the following directions toroughout this Treatise are suited. Now we may define the Declination of a Plain to be the Arch of the Horizon, contained between the true Points of East or West, and the Plain, equal whereto is the Arch of the Horizon between the true North or South, and that Vertical Circle or Azimuth that passeth through the Plains Poles. To find the Declination of a Plain. Upon a Board, having one straight smooth edge, draw a Line parallel thereto, and thereon describe a Semicircle, with the Radius of the Chords, which distinguish into two Quadrants by a perpendicular from the centre; then holding the Board parallel to the Horizon, and applying the straight edge to the Wall, hold up a thread and Plummet, so that the shadow thereof may pass through the centre, and in the shadow, make a mark near the Limb, from which a Line drawn into the centre shall represent the shadow of the thread. In this scheme, let ☉ C represent the shadow of the thread passing thorough the centre; at the same instant, take the sun's Altitude, and by the following directions, find the sun's true Azimuth. Admit the Sun be 75d to the Eastwards of the South, prick it from ☉ to S, than the distance between P and S shows the quantity of the Plains Declination, and the Coast is also shown, for if P fall to the Eastwards of S, the Declination is Eastwards, if to the Westwards of it, it is Westward; in this Example it is 30d Eastwards. We may suppose that the Reader knoweth which way from the Line of shadow to set of the sun's true Coast, that he may easily do by observing the Coast of his rising or setting, or whether his Altitude increase or decrease, and needs no directions. A General Proportion for finding the Azimuth. As the cousin of the Altitude, Is to the Secant of the Latitude, Or as the cousin of the Latitude: Is to the Secant of the Altitude; So is the difference of the Versed Sines of the sun's distance from the elevated Pole, and of the Ark of difference between the Latitude and Altitude. To the Versed Sine of the Azimuth from the North in this Hemisphere. Declination 23d 31′, North. Latitude 51d 32′ Altitude 41d: 34′ Azimuth 105d from the North Upon C as a centre, describe the Semicircle EBM, and draw ECM the Diameter, and CB from the centre perpendicular thereto, from B set off the Declination to D, the Latitude to L, the Altitude to A; and draw the Line CA continued. The nearest distance from D to BC when the Declination is North, place from C towards M when South towards E, and thereto set K, assuming the Diameter EM to represent the Secant of the Latitude, the Radius of the said Secant shall be the cousin of the Latitude doubled; wherefore the nearest distance from L to CM doubled, shall be the Radius to the said Secant, which prick on the Line of Altitude from C to Z, then the nearest distance from Z to CM shall be the cousin of the Altitude to that Radius, which extent prick from E to F, and draw the Lines EF and FM; then for the third term of the proportion, take the distance between A and L, and prick it from M to G, from which point take the nearest distance to BC, and place it from C to X, so is the distance KX, the difference of the Versed Sines sought, which prick from F to Q, and draw QR parallel to FM, so is RM the Versed Sine of the sun's Azimuth from the North sought, and CR the Sine of it to the Southwards of the East or West, and BP the measure thereof in the limb, found by drawing a LIne from R parallel to GB; in this Example the sun's true ghost is 15d to the Southwards of the East or West. Note also, that the Point R may be found without drawing the Lines EF, QR by entering the extent KX, so that one foot resting on the Diameter, the other turned about, may but just touch FM. To make a Horizontal dial. A Plain is then said to be Horizontal, when it is parallel to the Horizontal Circle of the Sphere proper to the place of Habitation; these are such kind of dials as stand commonly upon posts in a Garden. By the former Directions, a true Meridian Line may be found, let it here be represented by the Line FM. A Horizontal dial for the Latitude of London, 51 degrees, 32 minutes. Cross the same with a perpendicular, to wit, the Line of Six, and draw an Oblong or square figure as here is done, wherein to write the hours, from M to C set off such a Radius as you intend to draw a Circle withal, which for convenience may be as big as the Plain will admit, and therewith upon C as a centre describe a Circle, and set off the Radius of the said Circle from F to d, from M to k, and draw the right Line Fd, then prick the Poles height or Latitude of the place from f to L, and from L to S, and through the point S draw the Line MS, and it shall represent the Cock or styles height from the point L, take the nearest distance to FM, and prick that extent from F to N on the Line Fd, than a Ruler laid from N to k, where it intersects the Meridian is the Regulating point, or point ☉, then from M divide the Circle into twelve equal parts for the whole hours, setting the Letters of the Alphabet thereto, and lay a ruler from the Regulating point to each of those Divisions, and it will intersect the Circle on the opposite side, from which Intersections, Lines drawn into the centre at M, shall be the hours Lines required, to be produced beyond the centre, as many as are needful, which shall be the hours before or after 6 in the Summer half year, the halfs and quarters are after the same manner to be inscribed, by dividing each equal division of the Circle into halfs and quarters. This Circular Dyalling, was in effect, published and invented by Mr. Foster in his book of a Quadrant, in Anno 1638. for the demonstration of this Work will demonstrate the truth of those Circular performances, which he Operates on the back of that Quadrant, but is more expressly hinted in his Posthuma, the demonstration whereof shall follow. Those that have plain Tables with a Frame, may have Tangent Lines put on the sides of their Frame; and then if a centre be found upon the paper under the Frame by the Intersection of a Ruler laid over those Tangents, the requisite Divisions of a Circle to any Radius that can be described upon the paper, will be most readily given without dividing any Circle or setting of Marks or Letters thereto, the Frame keeping fast that paper, on which the Draught of the dial is made, which may also be supplied from a Circle divided on pasteboard cut out, which is to be Laced upon a Board over the paper whereon the Draught is to be made. An upright full South dial. This is no other than a Horizontal dial, in that Latitude which is equal to the compliment of the Latitude of the place, you are in, only the hours must not be continued beyond the centre, and the Delineation requires no other directions than the former. On a direct North dial, in this Latitude, there will not be above two hours above, and two hours beneath each end of the Horizontal Line to be expressed, and the style will have the same Elevation and point upward. Horizontal dial An upright South dial In all upright North and South Plains, the Meridian or hour line of 12 is perpendicular to the Plains Horizontal line, if the Plain be direct the height of the style above the substile, is equal to the compliment of the Latitude. If the Plain be South Reclining, or North Inclining, the height of the style above the substile, is equal to the Ark of difference between the compliment of the Latitude and the Ark of reinclination, and if this latter Ark be greater than the former, the contrary Pole is elevated. If the Plain be South Inclining, or North Reclining, the height of the style above the substile, is equal to the sum of the Colatitude, and of the reinclination, and when this latter Ark is greater than the Latitude, the styles height will be greater than a Quadrant. Such Horizontal or direct South dials, both upright and leaning, whereon the stile hath but small Elevation, are to be drawn with a double Tangent Line without a centre, wherein the following directions for direct Polar plains, and those for other Oblique plains, whereon the stile hath but small elevation, will fully direct you. All Plains that cut the Axis of the World, have a centre; but if they be parallel thereto, the stile hath no Elevation. Such direct South Reclining, or North Inclining Plains, whose Arch of Reclination is equal to the compliment of the Latitude, are parallel to the Axis, and are called Polar plains; in these the Hour Lines will be Tangent Lines of any assumed Radius, and the parallel height of the stile above the plain, must be made equal to the Radius of the Tangent, by which the hours were set off. First draw the Tangent line CG, and perpendicular thereto ACB, upon C as a centre, with any Radius describe the Quadrant of a Circle HB, and prick off the Radius from C to A, from H to E, from B to D, from D to F, from F twice to G. A Ruler laid from A to E finds the point 1 on the Tangent CG for the hour line of one, and laid from A to D finds the point 2 for the hour line of two, the hour line of three is at the point H, of four at the point F, of five at the point G; thus are the whole hours easily inserted. Now to insert the halfs and quarters. Divide the Arches BE, ED, DH into halfs, and a Ruler laid from A to those divisions will find points upon CH, where all the half hours under 45d are to be graduated; and if a Ruler be laid from B to those respective divisions of the Quadrant BH, it will find points on the Tangent CG, where the whole hours and halfs are to be graduated above 45d, after the same manner are the quarters to be inserted; But in regard the halfs and quarters above 45d will by this direction be found with much uncertainty, I have added the help following. First, Divide the halfs and quarters under 45d as now directed, then for those above make use of this Table. In a direct South Polar dial. The distances of these hour lines. Are equal to the distances of these hour lines. 3 and 3 ¼ 3 ½ and 4 2 ¼ and 3 ¾ 4: and 4 ¼ 4 ¼ and 4 ½ 4 ¼ and 4 ¼ ¾ and 1 ¼ 1 ¼ and 2 ½ 1 ½ and doubled ¾ and 1 ¾ 3 ½ and 3 ¾ doubled: otherwise, 1 ¾ and 2 ¾ 2 and 3 ¾ This I do not assert to be absolutely true, but so near the truth, that there will not arrive above one thousandth part of the Radius difference in the greatest dial that is made, and will be more certain than any Sector, though of a Vast Radius, or then they can with convenience be pricked down the common way, by a Contingent Line, the meaning of the Table will be illustrated by one or two examples. The distance between the hour lines of two and a quarter, and three and three quarters will be equal to twice the distance between the hour lines of twelve, and one and a half. Also the distance between four and a quarter, and four and a half, is equal to twice the distance between three and a half, and three and three quarters; or it is equal to the distance between one and three quarters, and two and three quarters, but the former is nearer the truth. It will be inconvenient in such plains, as also in direct East or West dials, to express any hour line from the substile beyond 75d or 5 hours. To these I may add some other observations which were communicated by Doctor Richard Sterne, to Mr. Sutton, which may be of use to try the truth of these kind of Plains. 1. The distance between the hours of 3 and 4, is equal to the distance between the hours of 1 and 3. 2. The distance between the hours of 2 and 4, is double to the distance between the hours of 12 and 2. 3. The distance between the hours of 11 and 4, is doubt to the distance between 12 and 3, or to that between 9 and 12, and so equal to the distance between 9 and 3, also equal to the distance between 4 and 5. 4. The distance between the hours of 11 and 5, is double to the distance between the hours of 11 and 4, as also to the distance between the hours of 4 and 5, and between 9 and 3; and quadruple to the distance between 12 and 9, or between 12 and 3. These are absolutely true, as may be found by comparing the differences of the respective Tangents from the natural Tables. To draw a Polar direct South dial. Having drawn the Plains perpendicular in the middle of the Plain, let that be the hour line of 12, then assuming the stile to be of any convenient parallel height, that will suit the plain, making that Radius, divide a Tangent line into hours and quarters by the former directions, and prick them down on the Plain, upon a line drawn perpendicular to the Meridian or hour line of 12 on each side thereof, and through the points so pricked off, draw lines parallel to the Meridian line, and they shall be the hour lines required, as in the Example. To describe an Equinoctial dial. Such direct North Recliners, or South Incliners, whose reinclination is equal to the Latitude, are parallel to the Equinoctial Circle, and are therefore called Equinoctial dials, there is no difficulty in describing of these: Divide a circle into 24 equal parts for the whole hours, & afterwards into halfs & quarters, and place the Meridian line in the Plains perpendicular, assuming as many of the former hours as the Sun can shine upon for either face, and then placing a round wire in the centre for the style, perpendicular to the Plain, and the dial is finished. A South plain Declining 30d East Latitude 51-32′ page 13 page 17 A South dial Declin 30d East Latitude 51-32′ To prick off the Substile and stile's height on upright Decliners in their true Coast and quantity. On such Plains draw a Horizontal Line, and cross the same with a perpendicular or Vertical, at the intersection set V at the upper end of the Vertical Line set S, at the lower end N, at the East end of the Horizontal Line set E, at the West end W, prick off the Declination of the Plain in its proper Coast from S or N to D, and draw DV through the centre, the same way count off the Latitude to L, and from it draw a Line into the centre; in the same quarter make a Geometrical square of any proportion at pleasure, so that two sides thereof may be parallel to the Horizontal and Vertical Line, at the intersection of one of the sides thereof, with the Vertical set A, and of the other side, with the Horizontal Line, set B, and where the Latitude Line intersects the side of the square, set F. To prick off the Substilar. For Latitudes above 45d take BF, and prick it on the Line of Declination beyond the centre from V to O, and from the point O, draw the Line OC parallel to the Vertical Line, and produced beyond O, if need require, and thereon from C to I prick the side of the Square, and a line drawn into the centre, shall be the Substilar line; but for Latitudes under 45d prick the side of the square from V to O, and draw OC as before, and make CI equal to of, and a line from I drawn into the centre, shall be the Substilar line. Styles Height. From the Point I erect the extent OC perpendicularly to the substilar OI, at the extremity thereof set K, from whence draw a line into the centre, and the Angle juk will show how much the stile is to be elevated above the substilar line. In order to the Demonstration hereof, let it be observed that an Angle may be pricked off by Sines or Tangents in stead of Chords. To prick off an Angle by Sines or Tangents. As in the Scheme annexed, let BC be Radius, and let there be an arch pricked off with Chords, as BE; I say, if the Tangent of the said Ark BA be taken out of a line of Tangents to the same Radius, and be erected perpendicular to the end of the Radius, as BA, a line drawn from A into the centre, shall include the same Angle as was pricked off by Chords, as is evident from the definition of a Tangent. In like manner an Angle may be pricked off by Sines, the nearest distance from E to BC is the Sine of the Arch BE, so in like manner the nearest distance from B to EC, is the Sine of the same Arch; wherefore if with the Sine of an Arch from the end of the Radius be described another Ark, as F, and from the centre or other extremity of the Radius, a line drawn just touching the same, the Angle included between the said line, and the Radius shall be an Ark equal to the Ark belonging to the said Sine; and what is here done by a line of natural Sines or Tangents, by help of a Decimal line of equal parts, equal to the Radius' may be done by help of the natural Tables without them. Any Proportion relating to the sixteen cases of Sphoerical Triangles, amongst which the Radius is always ingredient, may be so varied, that the Radius may be in the third place, and a Tangent or a Sine in the fourth place, and then if the Ark belonging to the fourth Proportional be known, an Angle equal thereto may be pricked off by Tangents or Sines according to the nature of the fourth term, as beforth; if it be unknown, notwithstanding an Angle equal thereto may be pricked off with Sines or Tangents according to the nature of the fourth term, from the two first terms of the Proportion, because they are in such Proportion, the first to the second, as the Radius or third term is to the fourth; upon this Basis follows the demonstration of this Scheme. The Demonstration of the former Scheme for upright Decliners. 1. That the Substilar Line is true pricked off. Assuming VB equal to VA to be Radius, then BF becomes the cotangent of the Latitude, whereto VO is made equal, which becoming Radius, OC is the cousin of the Declination, and VC the Sine. Now one of the Proportions for finding the Substile distance from the Meridian is this following: As the Sine of the Plains Declination, Is to the Tangent of the Latitude: So is the Radius to the Tangent of the substile's distance from the Horizontal Line. From whence it follows, that if the Sine of the Declination be pricked on the Horizontal Line from the centre, as VC, and the Tangent of the Latitude, erected perpendicularly thereto, as CI equal to VA, it shall give a point from whence a Line drawn into the centre, shall be the Substilar Line. Now I am to prove that VA is the Tangent of the Latitude, thus it is made good: In a Tangent Line of 45d, if the Tangent of any part or ark of it be assumed to be Radius (as here FB the Cotangent of the Latitude equal to VO, which before was made Radius) then doth the said whole Tangent line (which in this case is any side of the Square) become the Tangent of that arks compliment: thus, VA becomes the Tangent of the Latitude, because the Radius is a mean Proportional between the Tangent of an Ark, and the Tangent of that Arks compliment; For, As the Cotangent of the Latitude BF, Is to the Radius BG, So is the Radius BF, to the Tangent of the Latitude BG, there being the like Proportion between the two latter, as the two former terms. 2. That the styles Height is true pricked off. To perform this, the cousin of the Declination OC, to that lesser Radius, was erected perpendicularly from the point I, in the Substilar 〈◊〉, and IK made equal thereto. Now one of the Proportions for calculating the styles height is: As the Secant of the Latitude, Is to the cousin of the Declination: So is the Radius, To the Sine of the styles Height. Consequently the stile's height may be pricked off from the two first terms of the Proportion, if it can be proved that VK is the Secant of the Latitude; here let it be remembered that up is the Tangent of the Latitude, IP the Sine of the Declination, and IK the cousin. By construction the Angles VPI and VIK are right Angles, therefore the square of VI is equal to the two squares of up, and IP by 47 Prop. 1 Euclid; again the square of VK is equal to the two squares of IK and IV, wherefore the square of VK is equal to the sum of the three squares of IK, IP and up; but the squares of PI a Sine, and IK its cousin are equal to the square of the Radius. But the square of the Radius, and the square of up, the Tangent of the Latitude, is equal to the square of VK, therefore VK is the Secant of the Latitude, because the square of the Radius, more the square of the Tangent of any Ark, is equal to the square of the Secant of the said Ark. 3. That VK is equal to VF. Let VF be an assumed Radius, so will FB be the cousin of the Latitude. Again observe that in any line of Sines if the Sine of any Ark be made Radius, the whole line becomes the Secant of that Arks compliment, so here VK being the Secant of the Latitude is equal to VF the Radius, for let VT be made equal to VF, I say it holds as VO the cousin of the Latitude, is to the Radius VT, so is VO the Radius to VT the Secant of the Latitude, which is therefore equal to VK. Whence the trouble of raising a perpendicular in this Scheme, because the side of the square passeth through the compliment of the Latitude, is shunned the point K falling in the outward circumference. Lastly, from all this it unavoidably follows that VI is the cousin, and IK the Sine of the styles height to the Radius VF, which was to be proved. An upright South dial, Declining 30 degrees Eastwards, Latitude 51 degrees, 32 minutes. To draw the hour Lines of the former upright Decliner. First draw the Plains perpendicular CO, which for upright Plains is the Meridian line, and with the Radius VF of the former Scheme, draw an occult Ark upon C as a centre, and therein set off NV equal to TN of the former Scheme, and draw the line juc for the substile, and with the Radius VC describe a circle thereon. 1. The first work will be to find the Regulating Point in the Substile, called the Point Sol. Prick the Radius of the said Circle from I to P, and from C to Q, and draw the Line IP, and therein make IK equal to IK in the former Scheme, than a ruler said from K to Q, where it intersects the Substilar is the Regulating Point ☉. 2. To find a Point from whence the Circle is to be divided into 12 equal parts. Lay a Ruler from O to the point ☉, and it intersects the Circle on the Opposite side, at it set M. 3. To divide the Circle. From the point M before found, lay a ruler through the centre V, and it will find a Point on the other side the circle, at it set f, the points Mf divide the Circle into halfs, and each half is to be divided into six parts, the Radius umh will easily divide each half into three parts, and then it will be easy to divide each of those parts into halfs, and so the whole Circle will be divided into 12 equal parts, and if it be desired to inscribe the half hours and quarters, than must each of those parts be divided into halfs and quarters. Having thus divided the Circle into 12 parts, distinguish them with the Letters of the Alphabet. 4. To draw the hour lines, and to number them. Lay a Ruler to each of those Letter divisions, and upon the Regulating Point ☉ in the substyle, and it will find points on the Opposite side of the Circle from which if lines be drawn into the centre at C' they shall be the hour lines required. 5. An inconvenience shunned. When the points through which the hour lines are to be drawn, fall near the centre, the hour lines cannot be drawn from the said points with certainty. In this case let any hour line near the said point be produced, if need require, and upon C as a centre with the Radius CV describe the Ark of a Circle from the produced hour-line, take half the distance between the point, where the produced hour line, cuts the Circle, and the point through which the hour line proposed is to be drawn, and prick that extent off in the Arch swept, setting one foot where the Arch swept cuts the hour line already drawn, from whence half the distance was measured, and the other foot will find a Point in the said Arch, through which the hour line desired is to pass: Thus we inscribed the hour line of three in the former dial. When the North Pole is elevated, the centre of the dial must be below, but when the South Pole is elevated, as in this example, it must be above, and the Point ☉ must be always found in the other part of the Diameter most remote from the centre. 6. The styles height may be transferred from the former Scheme into this, by pricking the Arch TK twice in this Circle, and it finds a point, from whence a line drawn into the centre, shall represent the style. That the hour lines are true Delineated. The Point Sol found in the Substile, divides the Diameter of the Circle drawn on the said Substile in such Proportion, as the Radius is to the Sineof the styles height, by reason of the equiangled Triangles, whose Bases bear such proportion as their perpendiculars. The next work performed by dividing the Circle into 12 equal parts, and finding points on the opposite side, by laying a ruler over those equal parts through the point Sol, carrieth on this Proportion. As the Radius is to the Tangent of the hour from the substile, So is the Sine of the styles height To the Tangent of the hour line, from the Substile, being the proportion used in all dials, whereby to set off the hours. In the third figure following, let BA represent the Substile, and let the Regulating Point be at M, so that BM bears such Proportion to MA, as the Radius doth to the Sine of the styles height, let the perpendicular BHE represent a line of Tangents, whose Radius is equal to BC, and the perpendicular AD, another line of Tangents to the same Radius both infinitely produced, and let BE represent the Tangent of some particular Arch or hour to be drawn, from E through the point M draw a right line to D, and the Proportion lies evident in right lines. As the Radius BM: Is to the Tangent of the hour line from the subtle BE ∷ So is the Sine of the styles height MA To the tangent of the hour line from the substile AD. If from every degree of a Tangent line, lines be drawn into the centre of the Circle proper to that Tangent, they shall divide that Quadrant to which they belong into 90 equal parts, this follows from the definition of Tangents, but if the lines be drawn from every degree of the said tangent to the extremity of the diamer, they shall divide a Semicircle into 90 equal parts by 20 Prop. 3. Euclid. because an Angle in the Circumference, is but half so much as it is in the centre. Thus the Semicircle BGA is supposed to be divided into 90 equal parts from the Tangent BE, by lines drawn to A, as is the line EGA, so is the other Semicircle from the other Tangent AD, by lines drawn to B, as is BFD; Now if it can be demonstrated that the points GMF are in a right line, it follows that the same Proportions may be carried on from the equal divisions of these Semicircles, as were done in the right Tangent lines BE and AD, this Proposition being very well Geometrically demonstrated by my loving friend Mr. Thomas Harvy; his Demonstration thereof shall hereafter follow. Having found the distance of the hour line, from the subsistle AB, if B be made the centre of the dial, the right line BF drawn into the centre, shall represent the hour line proposed, making the same Angle with the Substile, as was found by the proportion; note that no hour can be further distant on one side or other of the Substile than 90d, and the said Ark of distance will be found in one of the Semicircles, and if the centre were not placed in the Circumference, the Angle found would be extended beyond its due quantity, in all upright Decliners or leaning Plains: The first Proportion carried on, is this; As the Sine of the styles height: Is to the tangent of the distance between the Meridian and substile: So is the Radius: to the tangent of the inclination of Meridians: Whereby is found the point from whence the Circle is to begin to be divided into 12 parts for the whole hours with their halfs and quarters, and those equal divisions give the Angles between the Meridian of the plain, and the respective hours, called by some the Angles at the Pole, and then the work is the same as before: Now to the Proposition. Construction. The right lines AD, BE are parallel, and touch the Circle in the extremes of the Diameter AB, DE is drawn at pleasure, cutting the Tangents in D and E, and the Diameter in M, BD and AE cutteth the Circumference in F and G, it is required to be proved that the Points F, M, and G, are in a right line. Draw the lines MF, MG, first if AD be= BE than AM is= MB, for the Triangles ADM and BEM are equiangeld, therefore M is the centre. Again AD being= BE and the Angle DAB= EBA & AB common to both Triangles DAB, EBA therefore the Angles DBA, EAB are equal, and the double of them FMA, GMB the Angles at the centre, are also equal, wherefore FM and MG is one and the same right line which was to be proved. Secondly, if AD be not equal to BE, as in the second, third, & fourth schemes let BE be greater, and make BH= AD and by= AM, and draw the right line AH cutting the Circumference in K; draw likewise IK, IH, GK, and extend GK infinitely both ways, which shall be either parallel to AB (as in the second figure) or cut it in the point P one side or the other, as in the third and fourth figures, in each from the points A and B, and the centre C at right Angles to GK, draw the lines AO, BN, CL lastly draw BG, from which Construction it willfollow, That 1. HI is parallel to ED for HB is= AD and by= AM and the Angles HBI and DAM are equal, therefore the angle and= BME is= BIH wherefore HI is parallel to ED. 2. IK is parallel to MF for HB is= AD and the Angle HBA= DAB, and AB common to both the Triangles HBA and DAB, therefore the Angles HAB and DBA are equal, wherefore AK= BF, but AK being= BF and IA= MB, and the Angle KAI= MBF, therefore KI is parallel to MF. 3. The Triangles AHE and AGK, are equiangled, so also are the Triangles AHB and AGO, because the Angle AKG= ABG is= AEB and EAH common to both the Triangles AHE and AGK, therefore they are equiangled; again the Angles AHB and and AGO being equal, the right Angled Triangles ABH and AOG are also equiangled. 4. NL is equal to LO, because BC is equal to CA and NK is= GO, because KL is= LG; now in the equiangled Triangles ABH, AOG as BH: HA ∷ OG: GA and in the Triangles AHE, AGK as HA: HE ∷ GA to GK, therefore (ex equo) it will be as BH: HE ∷ OG: GK, but as BH: HE ∷ by: IM for IH is parallel to EM, therefore as by: in ∷ OG: GK but NK is= OG, therefore by: in ∷ NK: KG, but IC is half of IM and KL half of KG, therefore by: IC ∷ NK: KL, therefore by Composition of Proportion, as BC: IC ∷ NL: KL, alternately, as BC: NL ∷ IC: KL. In the second figure BC is= NL, therefore IC is= KL, wherefore (because IC is also parallel to KL) IK is parallel to CL, by like reason GM is also parallel to CL, but in the third and fourth figures the sides PC, PL of the Triangle PCL are cut Proportionally by the parallel BN, and as before, as BC: NL ∷ IC: KL, and as PC: PL ∷ BC: NL, therefore PC: PL ∷ IC: KL, wherefore IK is parallel to CL. Again as before, BC: NL ∷ IC: KL, But CM is= IC and IG is= KL, therefore as BC: NL ∷ CM: LG, but as hath been said, as BC: NL ∷ PC: PL, therefore as PC: PL ∷ CM: LG, wherefore because the sides PM: PG, of the Triangle PMG are cut proportionally in C and L, CL and MG are parallel one to another. Now in all the three figures it hath been proved that IK and MG are either of them parallel to CL, therefore they are parallel one to another, wherefore the Angle GMI is equal to the Angle KIB which before was proved to be equal to AMF, therefore the Angles GMI and AMF are equal one to another, wherefore FM and MG is one and the same right line which was to be proved. To draw an East or West dial. Let the hour line of six, which is also the Substilar line, make an Angle equal to the Latitude of the place, with the Plains Horizontal line, above that end of it that points to the Coast of the elevated Pole, then draw a line perpendicular to the Substilar line, which some call a Contingent line, and with such a Radius as you determine the style shall have parallel height above the Substile: divide a Tangent line of hours and quarters according to the direction for direct Polar Recliners, then through those divisions draw lines parallel to the Substile and they shall be the hour lines required; thus the hours of 5 and 7, are each of them Tangents of 15d from six, and so for the rest, let them be numbered on each side of six (being the Substile) for an East dial with the morning hours, for a West dial with the afternoon hours, the one being the compliment of the other to 12 hours, and therefore we have but one example, namely an East dial for the Latitude of London. How to fill this or any other Plain, with any determined number of hours, shall afterwards be handled. A West dial Reclining 50d Latitude 51-32′ An East dial Inclining 40d Latitude 50d To prick off the requisites of an East or West Reclining or Inclining dial in their true situation and quantity. In these Plains, first draw the Plains perpendicular, and cross it with a Horizontal line, which is also the Meridian line; in any one of the quarters, make a Geometrical square, as before directed for upright decliners, and from the Plains Vertical in the said quarter, count off the Latitude to L, and from the Horizontal line in the said quarter count off the Reclination or Inclination to R, and from L and R, draw lines into the centre, and where the Latitude line intersects the side of the square, set F. 1. To prick off the Substile. For Latitudes above 45d place BF from V the centre in the Horizontal line for Recliners Northwards, for Incliners Southwards, and thereto set O, and through the said point, draw a line parallel to the Vertical, and place the nearest distance from A to RV on the former parallel, from O for Recliners upwards to I, but for Incliners downwards, and a line thence drawn into the centre, shall be the Substile. 2. The styles height. Place the nearest distance from B to RV on a perdendicular raised from the point I in the Substile, and it finds the Point K, whence a line drawn into the centre, shall represent the style. In the other Hemisphere the words Northwards and Southwards, must be mutually changed. For Latitudes under 45′ The side of the square must be placed from V to O and of must be placed on the line of Reclination or Inclination from V to C, the nearest distance from C to VA placed on the perpendicular, passing through O for Recliners upwards, but for Incliners downwards, finds the Point I, through which the Substile is to pass, and the nearest distance from C to VB raised perpendicularly on the point I in the Substile, finds the point K for the style, as before. Demonstration. 1. For the Substile. In these Plains VB or VA being Radius FB is the Contangent of the Latitude and the nearest distance from A to RV, is the cousin of Reclination or Inclination to the same Radius, and the nearest distance from B to RV, the Sine thereof; this for Latitudes above 45, but for lesser Latitudes. of the Tangent of the Latitude was made Radius, and thereupon the Radius or side of the square be-became the Cotangent of the Latitude, and the nearest distance from C to VA was the cousin, and from C to VB the Sine of the Reclination or Inclination, so that the prescribed Construction in both cases erects the cousin of the reinclination on the Cotangent of the Latitude, which is made good from this proportion. As the Cotangent of the Latitude Is to the cousin of the reinclination from the Zenith So is the Radius: To the tangent of the Substilar from the Meridian. 2. For the style. A proportion that will serve to prick it off, is, As the Cosecant of the Latitude, is to the Sine of the reinclination, So is the Radius: To the Sine of the styles height. page 25 A West dial Reclining 50d Latitude 51 32′ A South plain Declining 40d East Inclining 15 deg A West Plain, Reclining 50 degrees, Latitude 51 degrees, 32 minutes. The Point Sol, Substile, style, and hour-lines, are all found after the same manner as in an upright Decliner, the Substile being set off from the Meridian line here, after the same manner as it was from the Meridian there. A South Plain Declining East 40 degrees, Inclining 20 degrees, Latitude, 51 degrees, 32 minutes. To prick off the Requisites in all Declining, Reclining, and Incliing Plains in their true Coast and quantity. Now followeth those Directions enlarged, which as I said in the Epistle, I received from Mr. Thomas Rice. UPon any Plain first draw a true Horizontal line, at the East end thereof set E, and at the West end W, 'cross the said line with a perpendicular, which may be called the Plains perpendicular, by some termed the Plains Vertical line, or line of Reclination, at the intersection of these two lines set V, and upon it as a centre describe a Circle (the Radius whereof may be equal to 60d of a line of Chords) at the upper end of the Vertical line set S, and at the lower end N. As the Declination is, set it off with Chords from S or N towards the true Coast, and at it set D, from whence draw a line through the centre; also set off the Latitude of the place the same way and in the same quarter, and at it set L, from which draw a line to the centre. From that end of the Horizontal line, towards which the declination was counted, set the Inclination (which as well as the Reclinais reckoned from the Zenith, the former being the Denomination of the under, the latter of the upper face) upwards towards S, and the Reclination downwards towards N, and at it set R, from whence draw a line through the centre to the other side, of the Circle. In the same quarter of Declination, draw HA parallel to the Horizontal line, and FG parallel to the Vertical line, in a Geometrical square, of like and of any convenient distance from the centre at pleasure, and where the Latitude line intersects the side of the square, let the letter F be placed. On the line of Declination beyond the centre, make VO equal to FG, and draw OB parallel to the Horizontal line, continued till it meet with the side of the square FG produced, at the point of concurrence, set B, and where it intersects the Plains perpendicular, set P, and draw OC parallel to the Vertical line cutting WE at C, and make HA equal to OC or BG, now by help of the three points A, B, C thus found, the requisites will be easily pricked off. 1. The Substilar line. The nearest distance from A to RV, set on the line CO (produced if need be) from C to I the same way the distance was taken from A, that is, if downward or upward, the other must be so too, will show where VI the Substilar Line is to be drawn. 2. The styles height. The least distance from B to RV, set on a perpendicular raised upon the Substile from the point I will find the point K, from whence draw a Line into the centre at V, and the Angle juk will show how much the style is elevated above the Substile, and if the work be true, VK and VF will be equal, whence it follows, that the trouble of raising the mentioned perpendicular may be shunned. 3. The Meridian line. The least distance from C to RV, set upon the Line OPB, from P on that side, which is farthest from the Line RV, will find the Point M, from whence a Line drawn into the centre, shall be the meridian Line. And I add that on all North Recliners in the Northern Hemisphere, the meridian Line must be drawn through the centre on the other side; and than the construction of the scheme will place it below the Plains Horizontal Line, which is its proper situation for the said upper face, and for the under face the scheme placeth it true without caution. 4. A Polar Plain how known. If the line RV fall just into B, the Plain is a Polar Plain, in such a Plain the style hath no height, but is parallel to the Axis, in this case the Inclination of Meridians must be known, directions for such Plains must afterwards follow. But if the line RV fall between the Points B and P, then must the Substile style and Meridian be all drawn through the centre, and stand beyond on the other side. Annotations on the former scheme. 1. That for Latitudes under 45d this construction of the scheme, supposeth the sides of the square produced, which will therefore be liable to large excursions or other inconveniences, wherefore for such Latitudes, I shall somewhat vary from the construction prescribed. 2. In finding the Substilar line, in stead of erecting CI upon VC, you may prick the same on the Vertical line VN, and thereto erect VC, and get the point I possibly with more certainty by finding the intersection of two Arks where the said Point is to pass. 3. In pricking off the Meridian line, the distance of C from the centre may be doubled or tripled, but so must likewise up, and the nearest distance from C to RV erected on a line drawn parallel to WE, passing through the Point P so found, and in stead of drawing such a parallel, the Point M may be found by the intersection of two Arks. 4. That this scheme placeth the requisites of all dials in their true coast and quantity, yet notwithstanding if this scheme be held before a Looking-Glass, the Effigies thereof in the Glass shows how the scheme would happen and place the Requisites, namely, the style, Substile and Meridian, for a Plain of the same Denomination, but declining to the contrary Coast. And if the face of the said scheme be laid upon a Window, and the Substile, style and Meridian be continued through the centre on the backside thereof, it shows you how these requisites are to be placed on the opposite side of the Plain, which being done, may be held before a Looking-Glass as before, and will be represented for the contrary Declination of that opposite face: the truth of all which will be confirmed from the scheme itself. This scheme for Declining, Reclining, or Inclining Plains, useth a new method of Calculation, derived from an Oblique Triangle in the Sphere, wherein there is two sides with the Angle comprehended, given to find both the other Angles, which is reduced by a perpendicular to two right Angled Triangles, from which the following proportions are derived. I shall therefore first deliver the said method, then demonstrate that the said proportions are carried on in the scheme; and lastly, from the Sphere, show how those proportions do arise. 1. To find a Polar Plains Reclination or Inclination. As the Radius, Is to the cousin of the Plains Declination, So is the Cotangent of the Latitude, To the Tangent of the Reclination or Inclination sought. 2. To find the distance of the Substile or Meridian line, from the plains perpendicular for a Polar plain. As the Radius, Is to the Sine of a Polar Plains Reclination, So is the Tangent of the Declination, To the Tangent of the Substilar line from the Plains perpendicular. 3. The Inclination of Meridians. As the Radius, Is to the Sine of the Latitude, So is the Tangent of the Declination, To the Tangent of the Inclination of Meridians. Affections of a Polar Plain. The Substilar on the upper face, lies above that end of the Horizontal line, towards the Coast of Declination, and the Meridian lies parallel to the Substile beyond it, towards that end of the Horizontal line that is towards the Coast of Declination. For Declining, Reclining, or Inclining Plains. First find a Polar Plains Reclination for the same Declination. Then for South Recliners and North Incliners, get the difference, but for North Recliners and South Incliners, the sum of a Polar plains Reclination, and of the Re Inclination of the plain proposed, and then it holds. 1. For the Substile. As the cousin of the said Ark of difference or sum according as the Plain leans Northward or Southwards, Is to the Sine of the Polar Plains Reclination, So is the Tangent of the Declination, To the Tangent of the Substilar from the Plains perpendicular. 2. For the styles height. As the Radius, Is to the cousin of the substile's distance from the Plains perpendicular, So is the Tangent of the Sum or difference of Reclinations, as before limited, To the Tangent of the styles height. 3. Meridians distance from the plains perpendicular. As the Radius, Is to the Sine of the Re Inclination, So is the Tangent of the Declination, To the Tangent of the Meridian from the Plains perpendicular. 4. Inclination of Meridians. As the Sine of the styles height, Is to the tangent of the distance between the Meridian and Substile, So is the Radius, to the tangent of the Inclination of Meridians. For South Recliners or North Incliners, the difference between the substile's distance from the plains perpendicular, and the Meridians distance therefrom, is equal to the distance between the Meridian and Substile; the like for such North Recliners or South Incliners, as Recline or Incline more than an Equinoctial Plain, having the same declination, but if they lean above it, or have a lesser Reclination, the sum is the distance between the Meridian and the Substile. The three first Proportions, besides the finding of a Polar Reclination, are used in the scheme for the placing of the Requisites, and the latter proportion in the Circular scheme for drawing the hours. Another proportion for finding the Inclination of Meridians by Calculation, is: As the cousin of the Latitude, Is to the sine of the substile's distance from the Plains perpendicular, So is the cousin of the Re Inclination of the Plain, To the sine of the Inclination of Meridians. The Reclination of an Equinoctial Plain to any assigned Declination, is necessary for the determining of divers affections: The Proportion to find it, is: As the Radius: Is to the cousin of the Plains Declination: So is the Tangent of the Latitude, To the Tangent of the Reclination sought. The upper face of an Equinoctial Plain, is called a North Recliner, the Meridian descends from the end of the Horizontal line opposite to the Coast of Declination, the Substilar line is the hour-line of six, and maketh right Angles with the Meridian line. Directions for the true Scituating of the Meridian and Substile suited to the former method of Calculation. 1. For Plains leaning Northwards. If a South Plain recline more than a Polar Plain, having the same Declination, the Plain passeth beneath the Pole of the World, the North Pole is elevated upon the upper face, the Substile and Meridian line lie above that end of the Plains Horizontal line, towards the Coast of Declination, the Substilar line being next the Plains perpendicular. For the under face being a North Incliner, the South Pole is elevated, the lines lie in the same position below the plains Horizontal line, and on the contrary side of the plains perpendicular. If a South Plains Reclination be less than the Polar Plains Reclination, the Plain passeth above the Pole, and the North Pole is elevated on the under face, being the inclining side. The Substile and meridian lie above that end of the Plains Horizontal line that is opposite to the Coast of Declination, the meridian being nearest the Plains perpendicular, for the upper face being a South Recliner, the South Pole is elevated, and the lines lie in the same Position below the Plains horizontal line, but on the contrary side of the plains perpendicular descending below that end of the Horizontal line, opposite to the Coast of Declination. 2. For Plains leaning Southwards generally on the upper face the North Pole is elevated on the under face the South Pole. To place the Substile. Such North Recliners whose Reclination is less than the compliment of a Polar plains Reclination, the Substile is elevated above the end of the Horizontal line contrary to the Coast of Declination, and on the under face, being a South Incliner, the Substilar is depressed below the end of the Horizontal line, opposite to the Coast of Declination. But when the Reclination is more than the compliment of the Reclination of a Polar plain, the Substile is to lie below the plains Horizontal Line, from that end opposite to the Coast of Declination. But for South Incliners, being the under face, the Substile is elevated above the end of the Horizontal line, opposite to the Coast of Declination. To place the Meridian. On all North Recliners the Meridian lies below the Horizontal Line from that end thereof, opposite to the Coast of Declination, because at noon the Sun being South, casts the shadow of the style to the Northwards. On the under face, being a South Incliner, it must always be placed below the Horizontal Line, below that end of it toward the Coast of Declination. These Directions suppose the Declination to be denominated from the situation of that face of the plain on which the dial is to be made, and the Horizontal line for all dials that have centres, is supposed to pass through the same. Now to the Demonstration of the former scheme. 1. 'Tis asserted that if RV fall into the point B, the plain is a Polar plain, in which case the style is parallel to the Axis of the world. Demonstration. Every Declining plain may have such a Reclination found thereto, as shall make the said plain become a Polar plain, and the proportion to find it, may be thus: As the Tangent of the Latitude, Is to the cousin of the Declination, So is the Radius, To the Tangent of the Reclination sought. In the former scheme. if we make FG the Cotangent of the Latitude Radius, the side of the square will be the Tangent of the Latitude, now VO equal to FG, being Radius, OC equal to GB, is the cousin of the Declination; wherefore a Line drawn into the centre from B, shall include the Angle of a Polar plains Reclination agreeable to the two first terms of the proportion, and to the directions for pricking off an Angle by Tangents. 2. That the substile is true pricked off. Upon V as a centre with the Radius VB, imagine or describe a Circle than is BG equal to up, the Sine of a polar plains Reclination, which is equal to HA, and the Ark comprehended between A and B, will be a Quadrant. But in a Quadrant any line being drawn from the limb passing through the centre, the nearest distance from the end of one of the Radij will be the Sine of the Ark thence counted, and the nearest distance from the other Radius thence counted, will be the Sine of the former Arks compliment; so in this scheme the nearest distance from B to RV, when a plain Reclines, is the Sine of the Ark of difference, but when it inclines of the sum of the Reclination of the Plain proposed, and of the Reclination of a Polar plain, and the nearest distance from A to RV, is the cousin of the said Ark. Make VQ on the plains perpendicular equal to IC, which is equal to the nearest distance from A to RV, and from the point Q erect the perpendicular QT, whereto the line PO will be parallel, and consequently there will be a proportion wrought: Thus it lies, As VQ the cousin of the sum of the Polar plains Reclination, and of the Reclination of the plain proposed, Is to PV equal to BG, the Sine of a Polar Plains Reclination. These two terms are of one Radius, namely VB, So is the tangent of the Declination QT, To the tangent of the substile's distance from the plains perpendicular PO, These two terms are to another Radius, namely QV, then if the Tangent of an Ark be erected on its own Radius, as here is QI equal to CV, and a line be drawn from the extremity into the centre, the Angle belonging to that Tangent shall be pricked off agreeable to the general direction. 3. That the styles height is true pricked off. The Proportion altered to bring the Radius in the third place will be, As the Secant of the substile's distance from the Plains perpendicular, Is to the tangent of the sum or difference of Reclinations, as before limited, So is the Radius, To the tangent of the styles height. In the scheme making VQ Radius, VI becomes the Secant of the substile's distance from the Plains perpendicular, and the nearstdiestance from B to RV, is the tangent of the difference or sum of the Reclinations, which when VB was Radius, was but the Sine thereof, the reason why it now becomes a tangent, is because the cosine of the said Ark VQ, is made Radius: But, As the cousin of any Ark, Is to the Radius, So is the Sine of the said Ark, To the tangent of the said Ark. Therefore the nearest distance from B to RV equal to IK, being erected thereon, and a line from the extremity drawn into the centre, shall prick off the styles height suitable to the two first terms of the former proportion, and to the general direction for pricking off an Angle by Tangents. 4. That the Meridian is true pricked off, the Proportion to effect it: Is, As the Cotangent of the Plains Declination, Is to the Sine of the Re Inclination, So is the Radius, To the tangent of the Meridian from the Plains perpendicular. If VC be made Radius, then is CO equal to up the Tangent of the compliment of the Plains Declination, and the nearest distance from C to RV, is the Sine of the Re Inclination to the same Radius, which is erected perpendicularly on up suitable to the two first terms of the proportion and the General Direction. Lastly, that VK is equal to VF, these Symbols are used, q signifieth square,+ for more or Addition,= equal. VBq= VQq+ IKq, the reason is because VB being Radius, VQ is the cousin of an Ark to that Radius, and IK the Sine by construction. VBq= VGq+ GBq, therefore these two squares are equal to the two before. If to the latter part of each of these Equations, we add QIq or rather its equal POq, the sum shall be equal to VKq. I say then VQq+ IKq+ POq= VKq, this will be granted from the former Demonstration for upright Decliners. Again, VGq+ GBq+ POq= VFq, therefore VF is equal to VK, this cannot be denied, because, VGq+ FGq= VFq. And the two squares GBq, or rather VPq+ POq are equal to GFq, which is equal to VOq by Construction. To draw the hour-lines for the former South Plain, Declining Eastwards 40 degrees, Inclining 15 degrees Latitude, 51 degrees, 32 minutes. First having assigned the centre of the dial, through the same draw the plains perpendicular, represented by the pricked line CN, and with the Radius of the former scheme upon C as a centre, describe an Occult Ark, and therein set off NV equal to the substile's distance from the plains perpendicular, and through the point V draw the Substilar, and upon V as a centre, describe the Circle, and prick off the Meridians distance from the the Substile in the former scheme, namely YX twice in this Circle from I to O, and draw CO for the Meridian, after the same manner set off the style, then find the Regulating point Sol, divide the Circle, and draw the hour-lines according to former Directions, and when hour-lines are to lie both above and below the centre, they are to be drawn through. To fit the Dyalling scheme, for Latitudes under 45 degrees. A South Plain Declining 50 degrees East, Inclining 20 degrees, Latitude 30 degrees. The former Construction would serve, if the sides of the square were produced far enough, but to shun any such excursion, make VO equal to the side of the square, and through the point F, draw a parallel to the Plains perpendicular, and where the parallel OP produced interesects it, is the point B, upon V as a centre, with the extent page 34 A South dial Declin 40d East Inclin 15′ Latit 52-32 A South plain Declin 50d East Inclining 20d at 30d A South plain Declin 30d East Reclining 34-31 at 51-32 page 35 A South plain Declin 30d East Reclining 25d Lat 51-32 page 37 VB, draw the Arch ZB, and prick off a Quadrant thereof from the point B, and it will find the point A, the point C is found no otherwise than before; and now having these three points, the whole work is to be finished according to those Directions, to which when the style hath a competent height, nothing need more be added, unless it be some examples. How to draw such dials whereon the style hath no elevation as Polar Plains, or but very small elevation, as in upright far Decliners, and many leaning Plains. These plains are known easily, for if the reinclination pass through the point B, the plain is a Polar plain, and the Substile is to be found by the former Construction, which the scheme makes the same with the Meridian: moreover, another Ark is to be found, called the Inclination of Meridians: The proportion to find it, is: As the Radius, Is to the Sine of the Latitude, So is the tangent of the Declination, To the tangent of the Inclination of Meridians. If CO be made Radius, CV will be the Tangent of the Declination, which enter on VL from V to K, and the nearest distance from K to SV shall be the Tangent of the Inclination of Meridians, which is to be pricked on its own Radius from P to M, and draw a line from the centre, passing through M to the limb, whereto set F, so is the Arch NF the Inclination of Meridians sought, to wit, the Arch of time between the substile and Meridian. To draw the hour-lines. First draw a perpendicular on the Plain VN, and upon V as a centre, describe the Arch of a Circle, and from the Dyalling scheme prick off the substile's distance, and draw IV which shall represent the same, as also the Inclination of Meridians from I to f, then upon V as a centre, describe as great a Circle as the plain will admit, and find the point f, therein also, by laying a Ruler over V the centre, and f in the former Circle, and from the said point divide the Circle into twenty four equal parts for the whole hours (but we shall not need above half of them) then determine what shall be the parallel height of the style above the Substile, and prick the same on the Substilar line, from V the centre to I, through which point draw a Contingent line at right Angles to the Substile, and laying a Ruler from the centre over each of the divisions of the Circle, through the points where it intersects the Contingent line, if lines be drawn parallel to the Substile, they shall be the hour-lines required, the hour-line that belongs to the point f being the Meridian-line or hour-line of 12, after the same manner are the halfs and quarters to be inscribed, if the Contingent line be too high, the centre V may be placed lower, if it be required, to fit so many hours precise to the Plain; first draw it very large upon some Floor, and then it may be proportioned out for a lesser Plain at pleasure, as was mentioned for East or West Plains. A South Plain, Declining Eastwards, 30 degrees, Reclining 34 degrees, 31 minutes. The scheme placeth all things right for Equinoctial Reclining Plains, without any further caution. To draw the Hour-lines on such Plains, where the style hath but small elevation. A South Plain Declining 30 degrees Eastwards, Reclining 25 degrees, Latitude 51 degrees 32 minutes. In these Plains, because the hour-lines will run close together, the dial must be drawn without a centre, by help of two Contingent lines, and first of all the Inclination of Meridians must be known, thereby is meant the Arch of time between the Substile and the Meridian line or hour line of 12, and that may be found several ways; here I shall follow the proportion in Sines before delivered. Making VI Radius prick the same on the Latitude line VL, and from the point found, take the nearest distance to the Horizontal line, place this extent from V to F, and draw CF; then take the nearest distance from R to the Plains Vertical SN, which place from V to Q, then draw QT parallel to FC, so is VT the Sine of the Inclination of Meridians, which may be easily measured in the limb by the Arch SY, by drawing a line parallel to the Plains perpendicular from the point T, or by pricking the same on HA produced, and laying a Ruler thereto, or by drawing the touch of an Arch with VT upon S as a centre, than a Ruler laid from V touching the outward Extremity of that Arch, finds the point Y. Moreover, we need not make VI Radius, but prick the nearest distance from L to we, from V upwards, than the nearest distance to the Plains perpendicular from the Intersection of the Substile, with the limb must be placed from V towards W, and from the two points thus found a line drawn, and the rest of the work, as before. To draw the Hour-lines. First draw the Plains perpendicular CN, and draw an Occult Arch, wherein prick down NY and NK, and draw the Substile and style as before, making the same Angles. Through any two points in the Substile, as at A and B, draw two right lines continued, making right Angles therewith. Draw a line parallel to the style at any convenient distance, which is to represent the new style, as here DE. Take the nearest distance from B to DE, and set it on the Substile from B to V, also the nearest distance from A to DE, and set it from V to C, through which point draw another line perpendicular to the Substile. Upon V as a centre, describe the Arch of a Circle of as large a Radius as the plain will admit, and from the substile on the same side thereof the Meridian happened in the former scheme, set off the Inclination of Meridians, and it finds the point M, from whence divide the Circle into 24 equal parts, and draw lines from the centre V through those parts, cutting both the Contingent lines B and C, the respective divisions of the Contingent line C, must be transferred into the Contingent line A, and there be made of the like distance from the substile as in the said line C, then lines drawn through the Divisions of the two Contingent lines A and B, shall be the respective hour-lines required. A South Plain Declining Eastwards 30 degrees, Reclining 25 degrees, Latitude 51 degrees, 32 minutes. After the same manner must such East and West Recliners or Incliners, that have small elevation of the style, and upright far decliners be pricked down, and in these plains the Meridian many times must be left out, the proportion to find the Inclination of Meridians for upright Decliners: Is, As the Radius, Is to the Sine of the Latitude, So is the Cotangent of the Plains Declination, To the Cotangent of the Inclination of Meridians. In the Dyalling scheme, making CV Radius, CO is the Cotangent of the Declination, which enter on the Latitude line VL, and take the nearest distance to SV, which extent pricked upon CO, and it finds a Point, through which a line drawn from the centre to the limb, shall show the inclination of Meridians to be measured from N. Otherwise: That we may not transfer large Divisions on the Contingent line from a small Circle, and that the Plain may be filled with any determined number of hours, such as by after Directions shall be found meet, draw any right line on a Board or Floor that shall represent the Plains perpendicular, as CN, and from the same set off the Substile and stile's height from the general scheme as before, drawing a line parallel to the style as DE, also a line perpendicular to the Substile, which I call the Floor Contingent, and that it may be large, let it be of a good distance from the centre; from the point of Intersection at Y, take the nearest distance to the parallel style, which prick from Y to V, and upon V as a centre describe as large a Circle as may be with convenience, and from the Substile set off the Inclination of Meridians therein to M (which Ark refers to V as its centre) and from the said Point divide it into 24 equal hours (or fewer, no more than are required) and laying a Ruler over V, and those respective divisions graduate them on the large Contingent line, I say from this large Contingent line thus drawn and divided, we may proportion out the Divisions of two (or many) Contingent lines that are lesser, and thereby fill the Plain with any proper number of hours required. Then in Order to drawing the hour-lines on the Plain. The first work will be to draw the larger contingent line on the plain, which may be drawn anywhere at pleasure: for performing whereof, note, that what Angle the Substile makes with the Plains perpendicular, the Contingent line is to make the same with the Horizontal line, and the compliment thereof, with the Vertical line; also draw another Contingent line above this, parallel thereto at any convenient distance. In the bigger Contingent line assume any two points to limit the outward most hours that are intended to be drawn on the Plain, as admit on the former Plain, I would bring on hours from six in the morning, to two in the afternoon, between the space A and B of the greater Contingent, take the said extent AB, and upon the point B at 2 of the Floor Contingent, describe an Ark therewith, to wit, L, then from A Draw the line all, just touching the outward extremity of the said Ark. I say the nearest distance from D to all, being pricked on the Plains greater Contingent from A to D, finds a point therein through which the style is to pass. Also the nearest distance from in to all, finds the space AY on the Plains greater Contingent, and through the point Y a line drawn perpendicular to AB, shall be the Substilar line. The style is to be drawn through the Point D, making an Angle with the Plains Contingent line equal to the compliment of its height above the Substile in this example 80d 57′, to wit, the Arch NY. The respective nearest distances to all, from each hour-point, in the Floor Contingent, being pricked on the Plains greater Contingent from A towards B, finds Points therein, through which the hour-lines are to pass. The next work will be to limit one of the extreme hours on the Plains lesser Contingent, and that must be done by proportion. As the Distance between the parallel stile and substile on the Floor Contingent, Is to the distance between the stile and substile on the Plains lesser Contingent, So is the distance between the substile and either of the extreme or outward hours on the Floor Contingent, To the distance between the substile, and the said outward hour on the Plains lesser Contingent. A South dial Declining 30d East Reclining 25d Lat 51-32 This proportion is to be carried on in the Draught on the Floor, place die from A to G on the Floor Contingent, and with the extent EG taken from the Plains lesser Contingent, upon G on the Floor Contingent, draw the Arch O, and from A draw a line touching the outward extremity of the said Arch, and let it be produced. The nearest distance from in to AO, being pricked on the Plains lesser Contingent, reaches from G to C, the point limiting the outward hour of six. Then if the nearest distances to the line AO, be taken from all the respective hours on the Floor Contingent, and placed on the Plains lesser Contingent from C towards F, you will find all the hours points required, through which and the like points on the Plains greater Contingent, the hour-lines are to be drawn. Here note, that the extent die on the Floor Contingent, may be doubled or tripled; if it be tripled it reacheth to H, also the extent EG on the plains lesser Contingent, is to be increased after the same manner, and an Ark therewith described on H before found, as Q, and by this means the line AO will be drawn and produced with more certainty, then by the Ark O near the centre. And what is here done by help of the styles distance from the Substile, may be done by help of the outward hour, if the distance of the said hour-line from the Substile be found Geometrically or by Calculation, for the said hour-line will make an Angle with the Plains Contingent lines, equal to the compliment of the Ark of its distance from the Substile. This Plain is capable of more hours which cannot conveniently be brought on. After the same manner are upright far Decliners to be dealt withal, and all other Plains having small height of style. But to limit the outward hours on Polar plains, and East or West Plains, the trouble will not be half so much. A South Plain Declining Eastwards 30 degrees, Reclining 25 degrees, Latitude 51 degrees, 32 minutes. A second method of Calculation for Oblique Plains. By the former method the Meridians distance from the Plains perpendicular is to be found, and the Polar Reclination Calculated. Then for South Recliners, or North Incliners, get the difference, but for North Recliners or South Incliners the sum, of the Polar Plains Reclination, and of the Reclination of the Plain proposed, and it holds. As the cousin of the Polar Plains Reclination, Is to the Sine of the former sum or difference, So is the sine of the Latitude, To the Sine of the styles height. Which Pole is elevated is elevated is easily determined, by comparing the Reclination of the proposed Plain with the Polar Reclination, and all other affections are to be determined, as in the first Method. Then for the Substile, and Inclination of Meridians. As the cousin of the styles height, Is to the Sine of the Plains Declination, So is the cousin of the Latitude, To the Sine of the substile's distance from the Plains perpendicular: And so is the cousin of the Reclination, To the Sine of the Inclination of Meridians. This method ariseth from the aforementioned Oblique Triangle in the Sphere, in which by help of two sides, and the Angle comprehended, the third side is first found, and the other Requisites by the proportions for Opposite sides and Angles. Proportions for upright Decliners. 1. To find the substile's distance from the Meridian. As the Radius, Is to the Sine of the Declination, So is the Cotangent of the Latitude, To the Tangent of the Substile from the Meridian. 2. Angle of 12, and 6. As the Radius, Is to the Sine of the Plains Declination, So is the Tangent of the Latitude, To the Tangent of the Angle between the Horizontal line and six. 3. Inclination of Meridians. As the Sine of the Latitude, Is to the Radius, So is the Tangent of the Declination, To the Tangent of the Inclination of Meridians: 4. Styles height. As the Radius, Is to the cousin of the Latitude, So is the cousin of the Plains Declination, To the Sine of the styles height. These Arks are largely defined in my Treatise, The Sector on a Quadrant. For East and West reincliners, The compliment of the Latitude of the place, is such a new Latitude: in which they shall stand as upright Plains, and the compliment of their reinclination is their new Declination in that new Latitude, having thus made them upright Decliners, the former proportions will serve to Calculate all the Requisites. In all upright Plains, the Meridian lieth in the plains perpendicular, and if they Decline from the South (in this Hemisphere) it is to descend or run downward; if from the North it ascends, and the Substile lieth on that side thereof opposite to the Coast of Declination. In East or West reincliners, it lieth in the plains horizontal line, on the Inclining side the South Pole is elevated, but on the upper side the North Pole, and the Substile lieth above or below that end of the Meridian line, which points to the Pole elevated above the Plain. On all plains whatsoever to Calculate the hour distances. As the Radius, Is to the Sine of the styles height above the substile, So is the tangent of the Angle at the Pole, To the tangent of the hour-lines distance from the substilar line. By the Angle at the Pole, is meant the Ark of difference between the Ark called the Inclination of Meridians, and the distance of any hour from the Meridian for all hours on the same side of the Meridian the Substile falls, and the sum of these two Arks for all hours on the other side the Meridian. All hours on any Plain go to the contrary Coast of their situation in the Sphere, thus all the morning or Eastern hours, go to the Western Coast of the plain, and all the evening or Western hours, go to the Eastern Coast of the Plain. A third Method of Calculation for leaning Plains, that is, for all sorts of Plains that do both Decline, and also Incline or Recline. They may be referred to a new Latitude, in which they shall stand as upright Plains, and then they will have a new Declination in that new Latitude; which two things being found, the former Proportions for upright Decliners will serve to Calculate all the Arks required. How this may be done on a Globe, is not difficult to apprehend, having set the Globe to your Latitude, let one of the Meridians of the ecliptic or Longitude in the heavens, represent a Declining Reclining Plain, this Circle intersects the Meridian of the place in two Points, the one above, the other beneath the Horizon: Imagine the Globe to be so fixed, that it cannot move upon its Poles, then elevate or depress the Globe so in the Meridian that the point of Intersection above the Horizon may come under the Zenith, then will the Pole of the world be elevated above the Horizon to the new Latitude sought, and where the Meridian of Longitude that represents the Plain intersects the Horizon it shows the new Declination. Or it may be thus apprehended: The distance between the Pole of the world, and that point of Intersection that represents the Zenith of the new Latitude, is the compliment of the said new Latitude, and the distance between that point, and the Equinoctial is the new Latitude itself; the new Declination is the compliment of the Angle between the plain and the meridian of the place, an Ark usually found in Calculation under this denomination. To find these Arks by Calculation. As the Radius, Is to the cousin of the Plains Declination, So is the Cotangent of the reinclination from the Zenith, To the tangent of the Meridional Ark, namely the Ark of the Meridian between the Plain and the Horizon. And this is the first thing Master Gunter and others find; for South Recliners North Incliners the one being the upper, the other the under face, get the difference between this Ark and the Latitude of the place, the compliment of the said residue, remainder, or difference, is the new Latitude sought; but for North Recliners or South Incliners, the difference between this fourth Arch and the compliment of the old Latitude is the new Latitude. To find the new Declination: As the Radius, Is to the cousin of the reinclination, So is the sine of the old Declination, To the sine of the new. This method is hinted to us in Mr. foster's Posthuma, also in his Book of Dyalling in Anno 1638, where he refers leaning plains to such a Latitude wherein they may become East or West Recliners, but that method is to be deserted, as multiplying more proportions than this, and doth not afford that instrumental ease for pricking down the hours that this doth. Affections determined. Such South Recliners, whose meridional Arch is less than the Latitude, pass beneath the Pole, and have the North Pole elevated above them, but if the meridional Ark be greater than the Latitude, they pass above the Pole, the North Pole is elevated on the under face, all other affections are before determined. If the meridional Arch be equal to the Latitude, the plain is a Polar plain; for plains leaning Southwards, if the meridional Arch be equal to the compliment of the Latitude, the plain is an Equinoctial plain, if it be more, the plain hath less Reclination than an Equinoctial plain, if it be less it hath more, and all affections necessary for placing (and Calculating) the meridian line were before determined. This method of Calculation finds the substile's distance from the meridian, not from the plains perpetdicular, wherefore it must be showed how to place it in Plains leaning Southwards, for plains leaning Northwards use the former directions. To place the Substile in North Recliners. In these plains the Meridian and Substilar are to meet at the centre, and not being drawn through, will make sometimes an Acute, sometimes an obtuse Angle. When the Plains Meridional Ark is greater than the Colatitude, they make an Obtuse Angle, in this Case, having first placed the Meridian line, above it prick off the compliment of the distance of the Substile from Meridian to a Semicircle. But when the Meridional Ark is less than the Colatitude, prick off the said distance itself above the Meridian line. In South Incliners. When the Plains Meridional Ark is greater than the Colatitude, the Substile and Meridian make an Acute Angle, when it is equal to the Colatitude, they make a right Angle, when it is less than the Colatitude they make an Obtuse Angle, and must be pricked off by the compliment of their distance to a Semicircle, the Substile always lying on that side of the Meridian, opposite to the Coast of Declination. A fourth Method of Calculation for leaning Plains. An Advertisement. In this method of Calculation for all Plains leaning Northward, both upper and under side their Declination is the Arch of the Horizon between the North and the Azimuth of the plains South Pole, so that their Declination is always greater than a Quadrant; But for all Plains leaning Southwards, both upper and under face, their Declination is the Arch of the Horizon between the North and the Plains North Pole, wherefore it is always less than a Quadrant; in this sense Declination is used in the following Proportions. As the Sine of half the sum of the compliments, both of the Latitude and of the Reclination, Is to the Sine of half their difference, So is the Contagent of half the Declination, To the Tangent of a fourth Arch. Again, As the cousin of half the sum of the former compliments, Is to the cousin of half their difference, So is the Contangent of half the Declination, To the tangent of a seventh Arch. Get the sum and difference of the fourth and seventh Arch, then if the Colatitude be greater than the compliment of the Reclination, the sum is the substile's distance from the plains perpendicular, and the difference the Inclination of Meridians. But if it be less, the difference is the substile's distance from the Plains perpendicular, and the sum the Inclinations of Meridians. To place the Substile. For Plains leaning Southwards, when the Angle of the Substile from the Plains perpendicul is less than a Quadrant, it will on the upperface lie above that end of the Horizontal line that is opposite to the Coast of Declination, and on the under face lie beneath it, but when it is greater, it will lie below the said end, on the upper face, and above it on the under face, but this will not be till the Reclination be more than the compliment of the Reclination of a Polar plain that hath the same Declination; for plains leaning Northwards the Directions of the first Method suffice. To place the Meridian. Either Calculate it, and place it according to the directions of the first and second Method, or else Calculate it by this Proportion. As the Radius, Is to the Sine of the styles height, So is the tangent of the Inclination of Meridians (when it is Obtuse, take its compliment to a Semicircle) To the tangent of the Meridian line from the substilar. For Plains leaning Northward, the first directions must serve, but for Southern Plains the second, because the distance of the Meridian is Calculated from the Substile supposed to be placed, and here the work is converse to that, for in that we supposed the Meridian placed, and not the Substile. For the styles height. As the Sine of the fourth Arch, Is to the Sine of the seventh Arch, So is the tangent of half the difference of the compliments both of the Latitude and Reclination, To the tangent of an Arch sought. How much the said Ark being doubled wants or exceeds 90d, is the styles height. In South Recliners, if the said Ark being doubled, is less than 90d, its compliment is the elevation of the North Pole, and the Plain falls below the Pole. But if the said Arch exceed 90d the Plain passeth above the Pole, and the excess is the elevation of the North Pole on the under face of a South Recliner, called a North Incliner, and the affections were determined in the first method where the Declination hath its Denomination from that Coast of the Meridian to which the Plain looketh. These methods of Calculation may not precisely agree one with another, though all true, unless the parts Proportional be exactly Calculated from large Tables in every Operation, which to do as to the Examples in this Book, my leisure would not permit; This last method is derived also from the former Oblique Triangle, the Proportions here applied, being demonstrated in Trigonometria Brittanica by Mr. Newton. The Demonstration of the former Proportions In projecting the Sphere, it is frequently required to draw an Arch through any two different Points within a Circle, that shall divide the said Circle into two equal Semicircles Construction. 1. Draw a line from one of the given points through the centre, for conveniency through that point which is most remote. 2. From the centre raise a Radius perpendicular to that line. 3. And from the said point draw a line to the end of the Radius. 4. From the end of the Radius raise a line perpendicular to the line last drawn, and where it intersects the former line drawn through the first point and centre, is a third point given, describe a Circle through these three Points, and the Proposition will be effected. Example. Let it be required to draw the Arch of a Circle through the two points E and F that shall divide the Circle BD into two equal parts. Operation. From E draw EG, through the centre A, make AD perpendicular thereto, join ED, and make DG, perpendicular to ED cutting EG in G, through E, F, and G, draw the Arch of a Circle which will divide the Circumference BDC into two equal parts in B and C, that is, if CA be drawn, it will pass through B, if not, let it pass above or below, as let it pass below and cut BFE in H. Demonstration. By construction EDG and DAG are right Angles; therefore □ AD= ▭ EAG by 13 Prop. 6 Euclid. because EDG being a right Angle, AD is a mean Proportional between EA and AG, but ▭ EAG should be= ▭ CAH by 35. Prop. of 3 Euclid. therefore ▭ CAH= □ AD. But □ AD= □ AI that is= ▭ CAI, therefore ▭ CAH= ▭ CAI which is absurd, therefore CI cannot pass below B, the same absurdity will follow if it be thought to pass above it, therefore CA produced, will fall in the point B, wherefore BDC is a Semicircle, which was to be proved: And hereof I acknowledge I have seen a Demonstration by the Learned teacher of the mathematics, Mr. John Leak, to this effect. To project the Sphere and measure off the Arks of an upright Decliner. Upon Z as a centre, describe the Arch of a Circle, and cross it with two Diameters at right Angles in the centre, whereto set NESW to represent the North, East, South and West. Prick off the Latitude from N to L, and lay a Ruler to it from E, and where it cuts NZ, set P to represent the pole. Prick off the Declination of the plain from E to A, and from S to D, and draw the Diameter AZB, which represents the plain, and DZC, which represents the Poles thereof. Through the three points CPD, draw the Arch of a Circle, and there will be framed aright Angled Triangle ZHP right Angled at H, in which there will be given the side ZP the compliment of the Latitude, with the Angle PZH the compliment of the Declination. Whereby may be found the styles height represented by the side PH, the substile's distance from the plains perpendicular represented by ZH, and the Angle between that Meridian which makes right Angles with the plain, and the Meridian of the place represented by the Angle ZPH, showing the Arch of Time between the Substile and meridian, called the Inclination of Meridians, from which Triangle are educed those proportions delivered for upright Decliners. To measure off these Arks. 1. The Substile. A Ruler laid from D to H, finds the point F in the limb, and the Arch CF is the measure of the substile's distance from the meridian, to wit, 21d 41′. 2. The styles height. Set off a Quadrant from F to G, lay a Ruler from G to D and where it intersects BZ, set ☉ which is the Pole of the Circle CPD, lay a Ruler from ☉ to P, and it intersects the limb at I, so is the Arch AI the measure of the styles height, to wit, 32d 32′ 3. Inclination of Meridian. Lay a Ruler from P to ☉, and it intersects the limb at T, and A South plain Declin 30d East Latitud 51d 32′ page 51 A West plain Reclining 50d Latitude 51d 32′ the Arch WT is the measure of the Inclination of meridians, to wit, 36d 25′. 4. Angle of 12 and 6. In like manner we may draw a Circle passing through the points WPE, as the pricked Arch PE doth, than in the Triangle ZPQ right Angled at P, we have the side ZP given, and the Angle PZQ to find the side ZQ, lay a Ruler from D to Q, and you will find a Point in the limb, the distance whereof from C is the measure of the Arch sought, to wit, 57d 49′, to be measured by projection as the Inclination of Meridians. Lastly the hour-lines, these are represented by meridians drawn through the Poles of the World, as in the Triangle HPQ there will be given the styles height PH, and the Angle HPQ, to wit, the Ark of difference between the Inclination of Meridians and the hour from noon, for all hours on that side of the meridian the Substile falls, but on the other side the sum of these two Arks, and this Angle is called the Angle at the Pole; the side required is HQ, the distance between the Substile and the hour line proposed, which must be any hour, though in this scheme it represents the horary distance of six from the Substile. To project the Sphere for an East or West Reclining or Inclining Plain, Latitude 51 degrees, 32 minutes, a West Plain, Reclining 50 degrees. Having drawn the Fundamental scheme, and therein set off the Latitude as before, count the Reclination from N to R, and by laying a Ruler, find the point A, through it and the North and South points draw the Arch of a Circle which shall represent the plain, find the pole thereof by setting off a Quadrant from R to G, then through the pole of that Circle ☉, and the pole of the World P, draw the Arch ☉ PR, then in the Triangle NHP right angled at H, we have given the side NP the Latitude, and the Angle PNH the Reclination, to find PH the stile's height, and NH the substile's distance from the Meridian, and the Angle NPH the Inclination of Meridians, which is also represented by the Angle BPS. 1. To measure the styles height. Set off a Quadrant from B to C, and draw a Line through the centre, and where it intersects the plain at F, is the Pole of the plains Meridian, lay a Ruler from F to H, and it cuts the limb at I. Also lay it thence to P, and it cuts the limb at K, the Arch IK is the measure of the styles height, to wit, 36d 50′ 2. The Substile. A Ruler laid from ☉ to H, cuts the limb at M, and the Arch NM is the measure of the substile's distance from the Meridian, to wit, 38d 59′. 3. The Inclination of Meridians. Set off a Quadrant from K to O, and lay a Ruler from it to F, and it intersects the Meridian of the plain at Q, than a Ruler laid from P to Q, finds the point T in the limb, and the Arch ST is the measure of the Inclination of Meridians, to wit, 53d 26′. Otherwise with less trouble lay a Ruler from P to F, and it intersects the limb at V, and the Arch EV is the measure of the Inclination of Meridians, as before. To project the Sphere to represent a Declining Reclining Plain. A South Plain Declining 40 degrees East, Reclining 60 degrees, Latitude 51 degrees, 32 minutes. Having drawn the fundamental Circle, pricked off the Declination, and found the pole point as before, prick the Reclination from B to I, and laying a Ruler to it from A, find the point R, and through the three points BRA describe a Circle, representing the plain, also from K find the pole thereof ☉, and through the two points P and ☉ draw the Arch of a Circle FG, representing the plains Meridian, at the intersection of the plain with the Meridian set Z, and draw the Arch of a polar plain through P to S, and there will be several Triangles Constituted, from which were derived the several Methods of Calculation. In the right Angled Triangle ANZ there is given NA the compliment of the Declination, and the Angle NAZ the compliment of the Reclination, whereby may be found ZN the plains meridional Ark, which taken from NP rests ZP the compliment of the new Latitude; also the Angle NZA which is the compliment of the new Declination, and hence were derived the Proportions for the third Method, likewise in the same Triangle may be found ZA the meridians distance from the Horizon. In the Oblique Angled Triangle CP ☉, there is given the side CP, the compliment of the Latitude, the side C ☉, the compliment of the Reclination with the Angle PC ☉, the compliment of the Declination from the South to a Semicircle, whereby may be found the Angle CP ☉, the Inclination of Meridians, and the Angle C ☉ P whereof the measure is RH the distance, of the Substile from the Plains perpendicular, and the third side P ☉, the compliment whereof is PH the stile's height, and from hence was derived the third method of Calculation suited to Proportions for finding both the unknown Angles of an Oblique Spherical Triangle at two Operations, when there is given two sides with the Angle comprehended between them. The first method of Calculation is built upon the perpendicular trigonometry, for the perpendicular PS reduceth the former Oblique Triangle, to two right Angled Triangles, to wit, the right Angled Triangle, PSC, and the right Angled Triangle PS ☉, both right Angled at S. In the right Angled Triangle PSC, we have CP given the Colatitude, and the Angle PCS the Declination to find SC a Polar plains Reclination thereto. Again, In Oblique Spherical Triangles, reduced to two right Angled Triangles by the demission of a perpendicular, it is a common inference in every book of Trigonometry, when two sides with the Angle comprehended are given, to find one of the other Angles: That, As the Sine of the Side between the Angle sought and perpendicular, Is to the Tangent of the given Angle, So is the Sine of the Side between the Angle given, and perpendicular, To the Tangent of the Angle sought. And so in that Oblique Triangle, the difference between the Reclination of the plain proposed, and the Polar plain is RS, then because R ☉ is a Quadrant, S ☉ is the compliment of the former Ark, therefore it holds: As s SO: t SCP ∷ s SC: t S ☉ P which is the very proportion delivered delivered in the said Method for finding the substile's distance. Then in the right Angled Triangled PS ☉, we have S ☉, and the Angle S ☉ P to find the side P ☉, whereby is got the styles height; the Inclination of Meridians is found in the Oblique Spherical Triangle by the proportion of Opposite sides and Angles. Lastly, in the right Angled Triangle ZRC, there is given RC, and RCZ to find RZ the distance of the Meridian from the plains perpendicular. To measure the respective Arks abovesaid. 1. The New Latitude. A Ruler laid from W to Z, and P will give you the Arch MO in the limb, the compliment of the new Latitude, to wit, 27d 40′. 2. The New Declination. The Ruler laid from the Plains Zenith at Z, to its Pole at ☉, finds the point Q in the limb, and the Arch SQ is the new Declination, to wit, 18d 56′. 3. The substile's distance from the Plains perpendicular. A Ruler laid from ☉ to H, finds the point T in the limb, and the Arch CT being 26d 26′ is the substile's distance from the Plains perpendicular. 4. The Meridians distance from the Plains perpendicular. A Ruler laid from ☉ to Z, finds the point V in the limb, and the Arch DV being 35d 56′ is the Meridians distance from the Plains perpendicular. 5. The styles height. Set off a Quadrant from G to X, and draw XC, where it intersects the plain as at Y, is the Pole of the Arch FG, then laying a Ruler from in to H and P, you shall find the styles height in the limb to be the Arch 2, 3, namely, 26d 6′. A South plain Declin 40d East Reclining 60d at 51-32′ page 55 A South plain Declin 30d East Reclining 25d Lat 51 32′ 6. The Inclination of Meridians. A Ruler laid from P to Y, intersects the limb at¶, the Arch W¶ is 20d 58′, and so much is the Inclination of Meridians. The Polar Reclination CS is 31d 19′. The scheme determineth all the affections of the plain. 1. It shows that H the point of the Substilar lies on that side the plains perpendicular, that is towards the Coast of Declination. 2. That Z the point for the place of the Meridian, lies towards the same Coast as before, but below the Substilar Line. 3. The Arch PH shows you that the North Pole is elevated above the upper or Reclining face. After the same manner may all the Requisite Arks be measured, and affections determined for all plains whatsoever. A South Plain Declining 30 degrees Eastwards, Reclining 25 degrees, or a North Plain Declining 30 degrees Westwards, Inclining ●● degrees. In this scheme we have the same Oblique Triangle PC ☉ reduced to two right Angled Triangles PSC and PS ☉, SC is the Inclination of a Polar plain, and RC the Inclination of the plain proposed, the difference is Sir, and the compliment of it, is the compliment of S ☉ to a Semicircle, because S ☉ is greater than a Quadrant, and the proportions are wholly the same, though the Triangle have sides greater than a Quadrant. The North Pole is elevated on the Inclining face, the Meridian Z lies from the plains perpendicular towards that end of the Horizontal Line, opposite to the Coast of Declination, the same way and beneath it lieth the Substilar. The compliment of the new Latitude ZP is 10d 10′ The new Declination, viz. the compliment of NZA is 26d 57′ The meridians distance from the Plains perpendicular RZ 13d 43′ The substile's distance therefrom RH 18d 22′ The styles height PH is— 9d— 3′ The Inclination of Meridians, to wit, the Angle CP ☉ 27d 18′ The Polar Reclination— CS— 34d 31′ A South Plain Declining 40 degrees East, Inclining 15 degrees, or rather a North Plain Declining 40 degrees West, Reclining 15 degrees. Here again the Oblique Triangle CP ☉ is reduced to two right Angled Triangles PSC and PS ☉, and Sir is the sum of the Polar Reclination SC, and the Re Inclination of the Plain proposed CR, and S ☉ is the compliment hereof, because ☉ R is a Quadrant, find the Equinoctial point AE. The Polar Reclination CS 31d 19′. The new Latitude ZAE is 32d 15′. The new Declination being the compliment of NZA is 38d 23′ The Meridians distance from the plains perpendicular ZR 12d 33′ The substile's distance from the plains perpendicular RH 32d 16′ The styles height PH is— 41d 30′ The Inclination of Meridians ☉ PC rather the Acute Angle ☉ PN is 55d 58′ The Meridian Z lies from the plains perpendicular towards the Coast of Declination on the Reclining side, but must be drawn through the centre, because the Sun at noon casts his shadow Northwards, unless in the Torrid or Frozen Zone, and the Substile Hlyes on the other side the plains perpendicular. A North Plain Declining 40 degrees Eastwards, Reclining 75 degrees. In this plain likewise the Oblique Triangle C ☉ P is reduced to two right Angled Triangles PS ☉ and PSC by the perpendicular PS which is part of the Arch of a polar plain, here CR more CS is equal to the sum of the Plains Reclination proposed, and of the Polar plains Reclination, which is greater than a Quadrant for the Arch R ☉ is a Quadrant; now the cousin of an Ark greater than a Quadrant is the Sine of that Arks excess above a Quadrant, wherefore the Sine of S ☉ is the cousin of the sum of both the Reclinations, and the Case the same as before. A South plain Declin 40d East Inclining 15d Lat 51d 72′ page 56 A North plain Declin 40d East Reclin 75d lat 51d 32′ Prick off a Quadrant from G to X, and draw XC, it cuts the plain at Y, a Ruler laid from Y to H, and P finds the points 2, 3 in the limb, and the Arch 2, 3 being 61d 31′, is the styles height; orther compliment thereof to a Semicircle might be found by measuring the Arch PF. A Ruler laid from ☉ to Z, finds the point V in the limb for the Meridian Line, from which draw a Line through the centre on the other side, and it will be placed in its true Coast and quantity from the Plains perpendicular at A, to wit, 39d 2′. The Inclination of Meridians, to wit, the Angle CP ☉ is 20d 30′, The new Latitude ZAE 26d 38′. The new Declination is 9d 35′ to wit, the compliment of KRB. The Polar Reclination CS is 31d 19′. The truth of this Stereographick Projection is fully handled by Aguilonius in his optics, and how to determine the affection of any Angle of an Oblique Spherical Triangle, I have fully showed in a Treatise, called the Sector on a Quadrant. For the Resolution of Spherical propositions, Delineations from proportions or the Analemma, will be more speedy and certain (though they may also be thus resolved) which I have handled at large in the Mariners Plain Scale new plained. To determine what hours are proper to all kind of Plains. To do this it will be necessary to project upon the Plain of the Horizon, the Summer and Winter Tropics. Get the Sum and difference of the Colatitude, and of the Suns greatest Declination, so we shall obtain his greatest and least Meridian Altitudes. The depression of the tropic of Cancer under the Horizon, is equal to the least Meridian Altitude, and the depression of the tropic of Capricorn to the greatest. Example: 38d 28′ Colatitude 23d 31′ 61d 59′ greatest 14d 57′ lest Meridian Altitude, having drawn the Primitive Circle, &c. as before. Prick 14d 15′ from S to C, and 61d 59′ from S towards W, a Ruler laid from the points found, will intersect the meridian ZS at the point L for the Winter Tropic, and K for the Summer Tropic, through which the Circles that represent them are to pass, to find the Semidiameters whereof, set off their depression from N towards E, thus 14d 57′ the depression of the Summer Tropic terminates at O, a Ruler laid from E to ☉, finds the point X in the meridian SZN produced, so is XK the Diameter of the Summer Tropic, which being divided into halfs, will find the centre thereof whereon to describe it. In like manner is the Diameter of the Winter Tropic to be found; or if the Amplitude be given (or found as elsewhere is showed) which at London is 39d 54′, and set off both ways from G and E we shall have three points given through which to draw each tropic, and the centres falling in the Meridian Line will be found with half the trouble, as to find a centre to three Points. Also Project the Pole Point P as before, being thus prepared FKG will represent the Summer and HLI the Winter Tropic. Let it be required to know what hours are proper for a South plain Declining 30d Eastwards, through the three points BPA describe the the Arch of a Circle BQP, then laying a Ruler from B to Q, find the point R in the limb, and from it set off a Quadrant to M, than a Ruler laid from B to M finds the point ☉ the Pole of the hour Circle BQP, then laying a Ruler from P to ☉, it finds the point T in the limb, and the Arch ET being 65d 40′ is the measure of the Angle BPS, which turned into Time is 4 ho. 23′ prope, and showeth that at no time of the year the Sun will shine longer on the South side of this plain, then 23 minutes past 4 in the afternoon. In like manner if the Arch of a Circle be drawn through the two points PV, we may find the time when the Sun will soonest in the morning begin to shine on the South side of this plain. A South plain Declin 30d East at 51d 32′ page 61 A South plain Declin 60d East Reclining 40d at 51-32′ So if there were a South plain Declining 60d Eastwards, Reclining 40 degrees here represented by BRA, if it were required to know what hours are proper for the upper, and what for the under face, than where the plain intersects the Tropics as at I and K, draw two Meridians into the Pole at P, to wit, IP and KP, and first find the Angle IPZ, as was before showed, to wit, 53d 14′ which in time is 3 hours 33 minuutes, showing that the Sun never shines longer on the upper face of the Plain, then 33 minutes past 3 in the afternoon, which is capable of receiving all hours from Sun rising to that period of time, and the Angle KPZ, to wit, 39d 50′ in time 2 hours 39 minutes, shows that the Sun never begins to shine sooner on the under face then 39 minutes past 2 in the afternoon after, which all the hours to sunset may be expressed. To find these Arks of time by Calculation, there must be given the styles height above the Plain 15d 22′, PH, and the compliment of the Inclination of Meridians to a Semicircle, 136d 32′, to wit, HPS, then in the right Angled Triangle PHI there is given PH the stile's height, PI the compliment of the Declination, besides the right Angle at H, to find the Angle IPH 83d 18′ which taken from the compliment of the Inclination of Meridians HPS, there rests the Angle IPS the Arch of time sought, to wit, 53d 14′. The ascensional difference may be found by drawing the Arch of a Circle through the three points TPF, and thereby the length of the longest day determined that no hours be expressed, on which the Sun can never shine. Another manner of Inscribing the hour-lines in all Plains having centres. The method here intended, is to do it in a parallelogram from the Meridian line, whence the hour-lines may be pricked down by a Tangent of three hours, with their halfs and quarters from a Sector, without collecting Angles at the Pole, or by help of a scheme which I call the Tangent Scheam, the foundation of this Dyalling supposeth the Axis of the world to be inscribed in a Parallelipiped on continued about the Axis, the sides whereof are by the plains of the respective hour Circles in the Sphere divided into Tangent-lines, that is to say, each side is divided into a double tangent of 45d set together in the middle, and the said parallelipiped on being cut by any Plain, the end thereof supposed to be intersected, shall be either a right or Oblique Angled parallelogram, and then if from the opposite tangent hour points on the sides of the intersected parallelipipedon, lines be drawn on the Plain, they shall cross one another in a centre, and be the hour-lines proper to the said plain, but of the Demonstration hereof, I shall say no more at present, the inquisitive Reader will find it in the Works of Clavius. To draw the Tangent Scheam. I have before in Page 10 showed how to divide a Tangent Line into hours and quarters, which in part must be here repeated; draw any right Line, as MABH, from any point therein as at B, raise a perpendicular, and upon B as a centre, describe the Quadrant CH, and prick the Radius from B to A, from C to G, from H to F, and laying a Ruler from A to F, and G, you will find the points D and E upon the perpendicular CB, I say the said perpendicular is divided into a Tangent line of three hours, and the halfs and quarters may be also divided thereon, by dividing the Arches CF, FG, and GH into halfs and quarters, than from those subdivisions, laying a Ruler to A, the halfs and quarters may be divided on, as were the whole hours. Being thus prepared, draw the Lines MB, LE, KD, and IC, all parallel one to another, passing through the points B, 1, 2, 3. In this scheme they are perpendicular to BC, but that is not material, provided they pass through the same points, and are parallel one to another, yet notwithstanding the points A and H must be in a right Line perpendicular to CB. This scheme thus prepared, I call the Tangent Scheam, because a Line ruled any way over it, shall be divided also into a Tangent of the like hours and quarters, whence it follows that one of these schemes may serve to inscribe the hour-lines into many dials, which I shall next handle. To inscribe the Hour lines in a Horizontal dial. Having drawn the Meridian line M, XII, and perpendicular thereto the hour-line of six, Let it be observed that the sides of the Horizontal dial in page 8. to wit VI, ix., and VI, III and ix., III, are a right Angled Parallelogram, the one side whereof being the Diameter of the Circle being Radius, the other side thereof must be made equal to the Sine of the Latitude, in that scheme the nearest distance from L to MF was the Sine of the Latitude or styles height, the Semidiameter of the inward Circle, being Radius, and that extent being doubled and pricked from M to VI on each side, as also from F twice to ix. and III, by those extents the Parallelogram was bounded, the side III, F ix., being parallel to the Horizontal Line. Then take the extent MF from the Horizontal dial, and place it in the Tangent Scheam from M to O, and draw the Line MO, and the respective Divisions of the said Line being cut by the parallels of the Tangent Scheam are the same with the Divisions of the hour-lines on the inward sides of the Horizontal dial VI, ix., and VI, III, and from the tangent Scheam they are to be transferred thither with Compasses. Also place F, ix. or F, III from the Horizontal dial into the Tangent Scheam from M to N, and draw the line MN, which being cut by the parallels of the tangent Scheam, the Distances of those Divisions from M are to be pricked down in the Horizontal dial, the first from F to XI, and I the second from F to X and II, &c. To inscribe the hour-lines in a direct erect South dial. The Diameter of the Circle in the South dial in page 8, is the same as in the Horizontal, and the nearest distance from L to FM was the cosine of the Latitude, and was pricked twice on the Horizontal Line from M to VI on each side, whereby that inward Parallelogram was limited. Wherefore the divisions of the Line MO in the Tangent Scheam, are the same with the hour distances in this dial on the sides VI, III, and VI, ix.; then for the divisions of the hours on each side of XII, take the extent XII, ix. or XII, III, and because it is less than the outward parallel distance of the sides of the Tangent Scheam, having therein made MI perpendicular to BM, place this extent from I to P, and draw the line MP, then prick the extent RL from the Tangent Scheam, from F to XI and I, and the extent QK, from F in the dial, to X, and II, and from the hour points so found, draw lines into the centre at M, and they shall be the hour-lines required. To delineate an upright Decliner in an Oblique Parallelogram. An upright South dial Declining 30 degrees West, Latitude 51 degrees, 32 minutes. First draw the Meridian or Plains perpendicular CN, and upon C as a centre, with the Radius of the Dyalling scheme, describe A South plained Declin 40d East Reclining 60d Lat 51d 32′ page 64 A North plain Declin 60 West Inclining 60d Lat 51-32′ place this anywhere page 65 A South plain Declin 30d West Latitude 51d 32′ A South dial Declin 40d East Inclin 15d Lat 51d 32′ In Latitudes under 45d the side of the square AV must be assumed to be the Cotangent of the Latitude, the Radius whereto will be of the Tangent of the Latitude, to which Radius being pricked on the side of the square from the centre, the Sine of the declination must be taken out as before, and erected on the Cotangent of the Latitude, and this work must be performed on that side of the centre on which the Substile lies. To fit in the Parallelogram. Produce the Lines WE, VD, and VL, in the Dyalling scheme far enough, then assuming any extent to be Radius, enter it on the lines VD and VL from the centre to Y and Z, the nearest distance from Y to we is the Cofine of the Latitude to that Radius which enter on the Line of 6 or GC, so that one foot resting thereon, the other turned about may just touch CN, at the point found set H, and make CI on the other side equal to CH. The nearest distance in the Dyalling scheme from Z to we, is the cousin of the declination to the former Radius, which prick on the Meridian line from C to L. And draw a Line through L parallel to HI, and therein make LP, LQ each equal to CH, and draw HP and IQ, and there will be an oblique Parallelogram constituted, the sides whereof will be Tangent Lines. Nota, we might assume the point G in the hour-line of six, for the Parallelogram to pass through, and the nearest distance from D to we in the dyalling scheme, would be the cousin of the declination to the same Radius to be pricked on the Meridian Line as before. To inscribe the hour-lines. In the following Tangent Scheam made as the former, produce CB, and make BQ equal to BC, then take the extent PQ on the dial, and upon Q as a centre describe the Ark Y therewith, and draw the Line YC just touching the extremity, than you may proportion out the hours in this manner. If a line be drawn in the dial from H to L, and from L to I, the hour-lines being drawn shall divide each of these lines into a double Tangent, and consequently the hour-lines may also be pricked off on the said lines, after the method now prescribed. For upright far Decliners and such plains as have small height of style, recourse must be had to former directions for drawing them with a double Contingent line, each at right Angles to the Substile. The foundation whereof is this, Any point being assumed in the Substilar line of a dial, the nearest distance from that Point to the style, is the Sine of the styles height, the Radius to which Sine is the distance of the assumed point in the Substilar line from the centre of the dial; Then in all dials the hour distances from the Substilar line are Tangents of the Angle of the Pole, the Sine of the styles height being made the Radius thereto, having finished the delineation of the dial, the style is to be placed directly over the Substilar line, without inclining to either side of the Plain, making an Angle therewith equal to its height above the same, for the Substilar line is elsewhere defined to be such a line over which the style is to be placed in its nearest distance from the Plain, therefore if the style incline on either side, it will be nearer to some other part of the Plain than the Substilar line, whence it comes to pass in places near the Equinoctial, if an upright Plain decline but very little, the Substile is immediately cast very remote from the Meridian. Another way to prick down the hour-lines in Declining leaning Plains. Every such Plain in some Latitude or other will become an upright Decliner: First therefore by the former directions prick off the Substile, style and Meridian, in their true Coast and quantity, and perpendicular to the Meridian, draw a line passing through the centre, and A South dial Declin 40d East Inclin 15d Lat 51d 32′ A North dial Declin 40d East Reclining 75d Lat 51d 32′ it shall represent the Horizontal line of the Plain in that new Latitude as hear us; from any point in the style as K, let fall a perpendicular to the Substile at I, and from the point I, in the substyle let fall a perpendicular to the Meridian at P. To find the new Declination. Prick IP on the substilar line from I to R, and draw RK, so shall the Angle IRK be the compliment of the new declination, and the Angle IKR the new Declination itself. To find the new Latitude. Upon the centre V with the Radius VK, describe a Circle, I say then that up is the Sine of the new Latitude to that Radius which may be measured in the limb of the said Circle, by a line drawn parallel to us, which will intersect the Circle at F, so is the Arch SF the measure of the new Latitude. To prick off the Hour-line of Six. This must be pricked off below the Horizontal line, the same way that the substilar lies: The proportion, is, As the Cotangent of the Latitude, Is to the Sine of the Declination, So is the Radius, To the Tangent of the Angle between the Horizon and six. If RK be Radius, then is up the Tangent of the new Latitude, but if we make up Radius, then is RK the Cotangent of the new Latitude. Wherefore prick the extent RK on the Horizontal line from V to N, and thereon erect the Sine of the Declination to the same Radius perpendicularly, as is NA, and a line drawn into the centre shall be the hour-line of six; the proportioning out of the Sine of the Declination to the same Radius, will be easily done, enter the Radius up from K to D, and the nearest distance from D to IK, shall be the Sine of the new declination to that Radius. To fit in the Parallelogram. This is to be done as in upright Decliners, for having drawn a line from the new Latitude at F into the centre, if any Radius be entered on the said line from V, the centre towards the limb, the nearest distance from that point to up the Meridian line, shall be the cousin of the new Latitude to that Radius. Again if the same Radius be entered on RK produced if need be, the nearest distance to VR (produced when need requires) shall be the cousin of the new Declination, and then the hour-lines are to be drawn as for upright decliners, nothing will be doubted concerning the truth of what is here delivered, if the demonstration for inscribing the Requisites in upright decliners be well understood, it being granted that Oblique Plains in some Latitude or other will become upright decliners. There are two Examples for the Latitude of London suited to these directions, in both which the Letters are alike, the one for a South Plain declining 40d Eastwards, Inclining 15d, the other for a North Plain declining 40d East, Reclining 75d. To find a true Meridian Line. For the true placing of an Horizontal dial, as also for other good uses it will be requisite to draw a true Meridian Line, which proposition may be performed several ways, amongst others the Learned Mathematician Francis van Schooten in his late Miscellanies demonstrates one, performed by help of three shadows of an upright style on a Horizontal Plain, published first without Demonstration in an Italian book of dyalling by Mutio Oddi. But if all three be unequal, as let AC be the least, erect three lines from the point A, perpendicular to AP, AC, AD as is of, AG, and AH equal to the styles height AE, and draw lines from the extremities of the three shadows to these three points as are FB, GC, and HD; then because AC is less than AB, therefore GC will be less than FB, by the like reason GC will be less then HD, wherefore from FB and HD cut off or subtract FI and HK equal to GC, and from the points I and K let fall the perpendiculars IL, KM, upon the Bases AB, AD, afterwards draw a line joining the two points M, L, and from the said points let fall the perpendiculars LN equal to LI, and MO equal to MK. Then because the two shadows AB and AD are unequal, in like manner FB and HD will be unequal; but forasmuch as FI and HK, are equal by construction, it follows that LI, KM, or LN and MO will be unequal, and forasmuch as these latter lines are parallel a right line that connects the points O and N, being produced will meet with the right line that joins M, L produced, as let them meet in the point P, from whence draw a Line to C, and it shall be a true line of East and West, and any Line perpendicular thereto shall be a Meridian line, thus the perpendicular AQ let fall thereon, is a true Meridian Line passing through the point A, the place of the stile or wire. Whereto I add that if MO & LN retaining their due quantities be made parallel it matters not whether they are Perpendicular to ML or no, also for the more exact finding the Point P, the lines MO and LN, or any other line drawn parallel to them, may be multipyled or increased both of them the like number of times from the points M and L upwards, as also from the points O and N downwards, and Lines drawn through the points thus discovered, shall meet at P without producing either ML or ON. See 15 Prop. of 5 Euclid. and the fourth of the sixth Book. The greater part of van Schootens Demonstration is spent in proving that ML and ON produced will meet somewhere, this for the reasons delivered in the construction I shall assume as granted, then understand that the three Triangles ABF, ACG and ADH stand perpendicularly erect on the plain of the Horizon beneath them, upon the right Lines AB, AC and AD, whence it will come to pass that the three points F, G, and H meet in one point, as in E the top of the style AE, and that the right lines FB, GC and HD are in the Conique Surface of the shadow which the Sun describes the same day by his motion, the top of which Cone being the point E. Wherefore if from those right Lines we subtract or cut off the right Lines FI, GC and HK being each of them equal to one another, then will the points I, C and K, fall in the circumference of a Circle, the plain whereof is parallel to the plain of the Equator; and therefore if through the points K and I such a Position a right Line be imagined to pass, and be produced to the plain of the Horizon, it will meet with ML produced in the point P, where ON being produced, will also meet with it; so that the point P being in the Plain of the Circle, as also in the plain beneath it, as also the point C being in each Plain, a right line drawn through the Points P and C will be the Common Intersection of each plain, and the line PC will be parallel to the Plain of the Equator, and is therefore a true Line of East and West, which was to be proved. On all Plains though they Decline, and Recline, or Incline, after the same manner may be found the Line PC, which will represent the Contingent Line of any dial, and a perpendicular raised upon the Line CP shall be the Substilar Line, which in Oblique Plains is the Meridian of the Plain, but not of the place, unless they are both Coincident from this manner of finding a Meridian Line on a Horizontal plain, nothing else can be deduced without more schemes: From the three shadows, may be had the three Altitudes, and the Meridian line being given, the Azimuths to those three shadows are likewise given, which is more than need be required in order to the finding of the Latitude of the place, and the Declination and Amplitude of the Sun, which because this scheme doth not perform of itself, I shall add another to that purpose. By three Altitudes of the Sun, and three shadows of an Index on an Horizontal Plain, to find a true Meridian Line, and consequently the Azimuths of those shadows, the Latitude of the place, the sun's Amplitude and Declination. Let the three shadows be CA, the Altitude whereto is of 22d, 28′ The second shadow CB, the Altitude whereto is BG 59d, 21′ both these in the morning, The third shadow in the afternoon CD the— Altitude whereto is— DH 18d, 20′ Let the Angle ACB be 70d, and the Angle BCD 135d, by following Operations we shall find that the shadow CA, is 10d to Southwards of the West, that the shadow CB is 60d to Northwards of the West, that the shadow CD is 15d Southwards of the East. Having from the three shadows pricked off the three Altitudes to F, G, and H, from those points to the shadows belonging to them, let fall the perpendiculars FI, GK, HL, which shall be the Sines of those Altitudes, and the Bases IC, KC, and LC shall be the Cosines, from the point K in the greater Altitude, draw Lines to the points I and L in the lesser Altitudes and produce those lines. From the points K and I, the Sines of the two Altitudes, are to be erected perpendicularly, thus KM is made equal to KG, and IN is made equal to IF, then producing MN and KI, where they meet as at W, is one point, where the plain of the sun's parallel of Declination intersects the plain of the Horizon; in like manner on the Base KL, the Sines of two Altitudes KG, and LH, aught to stand perpendicularly from the points K and L in their common Base, but if they retain the same height, and are made parallel to one another, a line joining the points of the tops of those Sines produced, shall meet with the line joining the points of their Bases produced, in the same point as if they were perpendicular. Thus KP and LQ are drawn at pleasure through the points K, and L parallel one to another, and KG is the Sine of the greater Altitude, and LO is equal to the Sine of the lesser Altitude, and these two points being joined with the Line OG produced, meets with the Line KL produced, in the point E, another point where the plain of the sun's parallel intersects the plain of the Horizon. Or you may double KG, and find, the point P, as also double LO and find the point Q, a line drawn through P and Q, finds the point E, as before, but with more certainty. If you join ewe it shall be a true Line of East and West, and a perpendicular let fall thereon from C the centre, shall be a true Meridian line to the perpendicular style or wire, as is CS. The Arch Sir is the sun's Amplitude from the North 50d 6′ the shadow being contrary to the Sun, casts his parallel towards the South. Draw KT parallel to SC, and it shall be the perpendicular distance between the Sine of the Suns greatest Altitude, and the Intersection of his parallel with the Horizon. Upon K erect KV equal to the Sine of the Suns greatest Altitude of the three KG, and the Angle KTV shall be equal to the compliment of the Latitude, for the Angle between the plain of any parallel of declination and the Plain of the Horizon, is always equal to the compliment of the Latitude, and if upon T as a centre with the Radius CS, you describe the Ark KX, the said Ark shall measure the compliment of the Latitude in this example 38d 28′ which being given together with the Sine of the Amplitude CY, it will be easy to draw a Scheme of the Analemma, whereby to find the sun's declination, the time of rising, and setting, his height at six the Azimuth thereto, the Vertical Altitude and hour thereto, &c. and many other propositions depending on the sun's motion, as I have elsewhere showed. The whole ground hereof is, that a right line extended through the tops of the Sines of any two Altitudes of the Sun taken the same day before his declination very, shall meet with the Plain of the Horizon in such a point where the Plain of the sun's parallel intersects the Plain of the Horizon, and finding of two such points, a line drawn through them, must needs represent the intersection of those two Plain; in the former Scheme the Sines of the two Altitudes are KM and IN, a line drawn through the bottoms of those Sines, as KI extended shall be in the Horizontal Plain, and the Line MN extended through the tops of those Sines is in the plain of the sun's parallel, as also in the Horizontal plain; now whether these Lines stand erect or no is not material, provided they retain their parallelism and due length, and pass through the points of their Bases I, K, for the proportion of the perpendiculars to their Bases, will be the same notwithstanding they incline to the Horizon. To Calculate the Latitude, &c. from three shadows. A usual and one of the most troublesome propositions in Spherical Trigonometry, is from three shadows to find the Latitude of the place: thus Maetius propounds it, and with many operations both in plain and Spherical Triangles resolves it. The first operations are to find the Suns 3 Altitudes to those shadows, and that will be performed by this proportion, As the Length of the shadow, Is to the perpendicular height of the Gnomon, So is the Radius, To the Tangent of the sun's Altitude above a Horizontal Plain, which proportion on other Plains will find the Angle between the Sun and the Plain or Wall. Next Maetius gives the distances between the points of the three shadows, and then by having three Sides of a Plain Triangle, he finds an Angle, to wit, the differences of Azimuth between the respective shadows, which Angle may be measured off the Plain with Chords. But propounding it thus, Three Altitudes of the Sun above a Horizontal Plain, with the differences of Azimuth between the three shadows belonging to those Altitudes, being given, let it be required to find the sun's true Azimuth, the Latitude of the place, and the sun's Amplitude. And how this may be Calculated from the former Scheme, I shall now show. In the Triangle ICK of the former Scheme, the two sides IC and CK, represent two shadows, and the Angle ICK is the Angle or difference of Azimuth between them, and the said sides IC and CK, are the Cosines of the Altitude proper to those shadows; now by seven Operations in right lined Triangles, we may find the proper Azimuth or true Coast of any of those shadows. 1. In the right lined Triangle ICK, having the two sides IC and CK, with the Angle between them ICK, at one operation may be found both the other Angles CIK and IKC. 2. In the same Triangle by another operation, may be found the Side IK. Then to proceed, draw Nf parallel to IK, and fM will be the difference of the Sines of both the Altitudes belonging to those shadows, whereby may be found KW. 3. The proportion lies, As fM the difference of the Sines of both those Altitudes, Is to fN equal to IK before found, So is KM the Sine of the greater Altitude, to KW sought. 4. 5. 6. By three like Operations may be found in the other shadow Triangle, the Angles CKL, and KLC, with the Side KE. Having proceeded thus far to the Angle IKC, add the Angle CKL, the sum is equal to the Angle WKE. 7. Then in the Triangle WKE, we have the two Sides thereof WK, and KE given, and the Angle comprehended by them, and at one Operation we may find both the other angel's EWK, and KEW, the compliment of the Angle TWK, is the Angle WKT. The difference between the Angles WKT, and IKC, is the Angle CKZ, which shows the sun's Azimuth from the Meridian proper to that shadow, which may be otherways found, for the difference between EKT and TKC, also shows it. By two other Operations the Latitude may be found. 1. As the Radius: Is to WK before found ∷ So is the Sine of TWK to KT: 2. As VK the Sine of the greater Altititude, Is to KT before found, So is the Radius, To the Tangent of the Latitude. By another Operation may be found the Amplitude CY, having found the Angle ZKC, the Angle CKp is the compliment thereof, than it holds: As the Radius, Is to CK the cousin of the greater Altitude, So is the Sine of the Angle CKp to CP, the difference between which, and Yp equal to TK, is YC the Sine of the Amplitude sought. To make any dial from three Shadows. The Geometrical performance of the former Proposition, is insisted upon by Clavius in his Book of the Astrolable, but▪ he mentioneth no method of calculation as derivable from it: from this proposition Monsieur Vaulezard a French Mathematician educeth a general method for making of dials, from three shadows of a Gnomon stuck into a wall at random, whereof he doth not so much as mention any demonstration; I shall endeavour to deliver the method thereof with as much perspicuity as I can. Every Plain in some place or other, is an horizontal Plain; admit an Oblique Plain in our Latitude, the Substilar line represents the meridian of that place, and any contingent line drawn at right Angles, thereto will represent a true line of East and West in reference to that horizon, and if the hours did commence at 12, from each side the substile, the dial here would show the true time of the day there. In every oblique Plain assuming any Point in the style, and crossing the style with a perpendicular to that Point, which shall meet with the Substile, the Point so found in the Substile, is the Equinoctial Point, in respect of the assumed Point in the style; hence we may infer that if these two Points and the Substilar line were given the centre of the Dial might be easily found, now the former construction applied to an oblique Plain, assumed to be an Horizontal Plain, in respect of some unknown place, will find the Equinoctial Point and the substilar Line, the style Point being assumed in the extremity of a Gnomon any ways placed or stuck in a wall at random. From the former Scheme it may be observed that the Sine of any of the three Altitudes being erected on the Perpendicular between the foot of that Sine and the sun's parallel▪ gave an Angle equal to the elevation of the Equinoctial above the Horizon, which is the thing sought in the following work, but the Sine of the greatest Altitude performs the proposition best. If a stick or pin be stuck into a wall for this purpose, and doth not make right Angles therewith, a Perpendicular must be let fall from the extremity thereof into the wall, which is called the perpendicular style, and the distances of the shadows; from the foot thereof must be measured thence, in respect of the tip of this perpendicular style the Equinoctial Point must be found, wherefore it will be convenient to assume the said perpendicular style to be the Sine of the greatest of the three Altitudes of the Sun above the Plain, which properly in respect of Us are Angles between the wall and the Sun. Up on this assumption it will follow, that the shortest shadow will be the cousin of that Angle, and the distance between the tip of the style, and the extremity of that shadow will be the Radius: now from the lengths of the three shadows, and the height of the perpendicular style, it will be easy to find the Sines and the Cosines of the Angles between the wall and the Sun. fig. 1a fig. 2a fig. 3a fig. 4a Being thus prepared, draw three Lines elsewhere as in the third figure meeting in a centre, and making the like Angles as the shadows did, and let them be produced beyond that centre, and have the same Letters set to them: make CH CG in this Scheme, equal to the nearest distances from H I to CB, and make CL equal to EC, in the former Scheme. Draw the lines IG, IH produced; and make HP GO equal to nearest distances from I H to BG, and parallel to HP and GO, draw the lines IN, IM, each of them made equal to CB, then draw the Hipotenusals MO, NP, meeting with the Bases at K and L, draw the Line KL, and it shall represent the Plains Equinoctial or contingent Line. From I, let fall the perpendicular IQ produced, and it shall be the Substilar line on the Plain and the Point Q is the Equinoctial Point sought. To place the Substile. Then repair to the Plain whereon you would make the dial represented by the first Scheme, and place CQ therein, so that it may make the same Angle with the shadow CE, as it doth with the Line IC in the third Scheme, and it shall be the Substilar Line, which is to be produced, also prick IQ from the third Scheme from C to Q on the Plain in the Substilar Line, and upon the point C, perpendicular to the Substile, raise the Line AC, and make it equal to CB, drawing the Line AQ, then will the Angle AQC be equal to the compliment of the styles height; for it is the Angle between the plain and the Equinoctial; just as before in the Horizontal plain, the Sine of the greatest Altitude was erected on a Line falling perpendicular from the foot of the said Sine, to the intersection of the plain of the sun's parallel with the plain of the Horizon, and thereby gave the Angle between the Suns parallel and the Horizon, equal to the compliment of the Latitude. To find the centre of the dial and stile's height. If from the point A you raise the Line AV perpendicularly to AQ, where it cuts the Substilar Line, as at V, is the centre of the Dial, and he Line AV represents the style. 3. To draw the Meridian Line. If the Plain recline, a thread and plummet hanging at liberty from the Point B, and touching the Plain, will find a Point therein, suppose K a line drawn from K into the centre of the Dial, shall be the Meridian line of the place. A broad ruler with a sharp pin at the bottom of it, being in a right line, with a line traced through the length of that ruler, whereto the plummet is to hang, having a hole cut therein for the bullet to play in, will find this Point in a reclining plain. On an inclining Plain, if the thread and plummet hang upon the style at liberty, to some part of the style more remote from the centre, fasten another thread, which being extended thence to the Plain just touching the former thread and plummet hanging at liberty, will find many Points upon the Plain, from any of which, if a line be drawn into the centre it shall be the Meridian line required; See the fourth figure: or in either of these cases hold a thread and plummet so at liberty that it may just touch the style, and bringing your sight so, as to cast the said thread upon the centre at the same by the interposition of the thread; the eye will project a true Meridian-line on the Plain, for the thread represents the Axis of the Horizon, and the Plain of the Meridian, is in the said Axis. If the centre fall inconvenient upon the Plain, it will be necessary to draw the Plains perpendicular, passing through the foot of the perpendicular style C, and measure the Angle of some of the shadows from it, and accordingly so place it in the third figure or draught on the floor, on which find the centre, and afterwards assign the centre on the Plain where it may happen convenient, and from the said draught, by help of the Plains perpendicular, set off the substile and stile's height; On plains on which probably the style hath but small height, the perpendicular style in this work must be assumed the shorter. 4. To draw the Hour Lines. These may be set off in a parallelogram after the Substile, style' and Meridian are placed which I have handled before. Or they may be inscribed by the Circular work, if we assume the perpendicular style AC, to be the Sine of the styles height, the Radius thereto will be AV, prick the said Radius on the Substile from V the centre to, Z, and upon Z as a centre, describe the Circle as in the first figure, and find the regulating point ☉ by former directions, over which from O the point where the Meridian of the place cuts the said Circle, lay a ruler, and it finds M, on the opposite side, being the Point from whence the Circle is to be divided into 12. parts, for the hours with subdivisions for the halves & quarters. Here note that the arch MV, is the inclination of Meridians, the whole Semicircle being divided but into 90d, and if that be first given (as hereafter) we may thereby find the Point O, whence the Meridian Line is to be drawn into the centre. 5. A Method of Calculation suited hereto. This is altogether the same as for finding the Azimuth of the shadows on the Horizontal Plain and as easy, whereby in the third figure, the Angle of the Substile CIQ, must be set off from the shadow ICE, just as the Meridian Line CP, might be set off from the shadow CK on the Horizontal. And the compliment of the styles height AQV, in the first figure here, as the compliment of the Latitude KTV, was found there. Lastly, for placing the Meridian Line of the place by calculation, the substile's distance from the plains perpendicular, and the reclination of the Plain must be found, which may be got easily at any time without dependence on the Sun, and then in the often-mentioned oblique Triangle in the Sphere, we have two sides with the Angle comprehended given, to wit, the compliment of the styles height, the compliment of the reclination, and the substile's distance from the plains perpendicular whereby may be found the inclination of Meridians: and consequently the Meridian line of the place, also the Latitude thereof, with the Plains declination, if they be required. To perform all this other wise Geometrically and instrumentally, (but not by calculation) there was an entire considerable quarto treatise, with many excellent Prints from brass-Plates thereto belonging, printed at Paris in France, in An. 1643. by Monsieur Desargues of Lions, which Treatise I have seen but not perused, a year after was published the small Treatise of Monsieur Vaulezard before mentioned. The inscribing of the signs, Azimuths, parallels of the longest day, &c. are lately handled by Mr. Leybourn in his Appendix to Mr. Stirrups Dyalling, as also by Mr. Gibson in his Algebra, who thinks in many cases that they deform a plain, and are seldom understood by the vulgar, wherefore it will not be necessary to treat thereof. The directions throughout this Book are suited to the Northern Hemisphere and are the same in the Southern Hemisphere, if the words South for North, and North for South be mutually changed. Since the Printing of this Treatise, I have not had time to revise it with the Copy, and so cannot give thee a full account of what faults may have escaped, which I think are not many; these few following be pleased to correct. Errata. Page 17 line 3 upon M read upon C. p. 15 l. 34 for Substilar Sine r. Substilar Line. p. 25. l. 12 for 20d r. 15d. p. 36 l. 17 for 51′. r. 31′. FINIS.