THE USE Of the Nocturnal. Written by W. P. The Nocturnals and these Books, are to be sold by Joseph Moxon, at his shop in Cornhill, at the sign of Atlas, in London. 1655. THE USE Of the Nocturnal. 1. What the Nocturnal is. IT is an Instrument consisting of two parts: 1. A Circle, which is divided into 24 hours; and each hour into so many parts as the space between each hour will admit of. The common Nocturnals are divided into four quarters, and each quarter into three parts; so as the whole hour is divided in 12 equal parts; each equal part containing five Minutes, as you may see in the Nocturnal itself; upon the hour of 12 there is placed a Flower de Luce. The second part of it is a movable Rundle, the Circle whereof is fixed to the Centre of the Circle of hours, that so you may turn it round, as occasion requires. The outmost edge of this Rundle is divided into 365 parts, showing the days of the year; and the next within this, is the Months of the year, marked with the first letter of each Month, as I. for January, F. for February, and so of the rest. And also in the Circle are divisions, numbered with 10, 20, 30, showing the number of days comprehended between the beginning of the Months, and the division to which these Figures are annexed. Within this Circle is described those fixed stars that are near the North-Pole, and belonging to five Constellations; whereof that which is in the middle, is called URSA MINOR, (of some HELICE MINOR) which in English is the little Bear, it being in the form a Bear. This Constellation consists of seven stars, whereof three only are splendent; that is the Pole star in the end of the Tail, and those two that are in the foreparts of the Bear, one of them upon his Back near the Neck, and the other upon his side; and these two are called of our Mariners the Guards, These three stars are of excellent use in Navigation, and well known by Seamen. The next Constellation is DRACO, or the Dragon, and hath sundry stars which you may learn to know by the Rules following. The third is BOÖTES. The fourth is CASSIOPEIA. The fifth is URSA MAJOR, or the great Bear. And lastly, there is six Lines drawn through the Pole, which are Meridian's, and are of great use, as you shall learn hereafter. Here followeth several Uses of the Circles of the Nocturnal. 1. The round Circle whereon the Rundle is fixed, which is divided into 24 hours, notes the 24 hours of the Night and Day, and also the quarters of every hour, and the third part of each quarter, which is but five Minutes; so that you may work to five Minute's of time by this Instrument, be it either time given, or time sought for as the question importeth. 2. The use of the Months, and their divisions into days, is either to give the day of the Month sought for, or by the day of the Month given, to find another thing required, as the question imports. 3. The use of the stars and their Constellations is twofold: 1. To learn to know those stars one from another, and from all other stars. And 2. Knowing them, to make use of them, ●s the question ye are to resolve requires. And note this, That that star which is in the Tail of the little Bear, is nearest the North-Pole, and as in the Rundle all the rest of the stars seem to move round this star, so do they in the Heavens seem to move round it also: This being an exact Type or Figure of the stars near the Pole. 4. The use of the Meridian's which run through the Pole: (or rather meet together in the Pole) Their use is threefold: 1. For the more ocular distinction of each Month. 2. To show the Right Ascension of any star described in the Rundle. And 3. To show how to bring any star to the Meridian of the Nocturnal, which is the hour of 12 under the Flowe● de Luce. Also because we seldom see a star just upo● the Meridian, therefore do these Meridian show how to place the star either short or pa●● the Meridian, which we could not do so we●● by guess. Thus much I judged meet, not only for th● use that these difinitions are of in the use of th●● Instrument, but because they may satisfy th● desire of some that are not versed in Mathematical Phrases, and yet would willingly kno● the reason of such things. Therefore to conclude this discourse with a few of the mo●● practical uses of this Instrument, that may be easily understood of those that are not Mathematically disciplined. First then, To learn to know the stars described in the Rundle one from another, and from the rest of the stars that we see in the Heaven. In a night when the stars may be seen, look toward the North part of the Heaven, and there you may take notice of seven very bright stars, lying in the same form as ye see in the Image of the great Bear; four lying in a square, or like the four Wheels of a Wagon, and three, which you may imagine to be three Horses following one another; the form how they lie, you may see in the Rundle between the letters A, S, O; these being well known, you may look what stars lie near any one of them, and there you will find what star it is. As for example. I see a star lying just over the star in the great Bears back: looking in the Rundle I find that star to be in the end of the Dragons-tayl, and so you may learn to know them all one from the other, comparing the stars ye see in the Heaven to them that are in the Rundle; and though you may see many stars in the Heaven, yet these are of the greatest magnitude amongst them. Another way to know the true name of a star, and to know it from others. First note a star in the Heaven, that you see upon, or near the Meridian; then look in the Nocturnal for the day of the Month, and bring that day to the hour of the night next the Flower de Luce, then look what star lieth between the Flower de Luce and the Pole in the Rundle, and that is the star, and its name which I see in the Heaven: but then if looking on the Rundle, I find two stars lying between the Flower de Luce and the Pole, than you must note which is nearest the Pole, and which furthest off, and so you may know each from other: And because to know the North-star is very expedient, I will show you how to do it, after I have given an example of what I last laid down. Upon the first of April, at half an hour past nine, I see two bright stars upon the Meridian, the one nearer me than the other; then to know the names of those two stars, and to know them from others, I bring the letter A for April to half an hour past nine from Noon, (the Flower de Luce noting Noon) and so counting 1, 2, 3, to half past nine, then looking in a right Line from the Flower de Luce to the Pole, I see the star nearest me as it lies in the Heaven, to be in the thigh of the great Bear; and that furthest from me, to be in the back of the Bear; and then looking a little to the East in the Heavens, I see two more follow in a Front, and after them cometh three more: for these I look in the Rundle, and one of the two next to the two I found on the Meridian, is upon the great Bear's buttock; the other in the root of his Tail: The first of the three following, I find to be thus: The first in the Tail, the second in the middle of the Tail, the third in the extremity or end of the Tail: And by this you may come to know all the stars inscribed in this Rundle. And this always note, That the star which in the Heaven ye find next to you, that star will appear next the edge of the Rundle; and this is when ye find two stars upon the Meridian at once. Now I shall show you how to find out the North-star, from the rest which you see in the Heaven; and this star is very bright, being one of the second magnitude or bigness. The most exact and speedy way is this: Take a Quadrant Astrolabe, or Crossstaff, and as near as you can guests, look (through the sights of your Instrument) into the North part of the Heaven, so high as is the Latitude of your place, and it will soon show you whereabout it is, for there is no star so great near it; and when you have thus found it, be sure you note it well how it lies from other stars, that you may know it again: Thus at London the Latitude being 51 Degrees and an half, I lift up the Sights of the Quadrant or Astrolabe, till the thread of the Quadrant, or Aledida of the Astrolabe fall upon 51 Degrees and an half; then looking still at that height, I look as near the North point as I can guests, and there, or very near is the Pole or North-star. If you have a Magnetic Needle that will show you the North point of Heaven. The next way to find the North-star is this, which is done without any Instrument. Look into the North part of Heaven, note some star that is little above half the height of Heaven, from the lower part of the Heaven; and by diligent notice, see whether in an hours time or more, you can see it remove from the place where you first saw it; if it be removed, that is not the star; and so continuing note the star that lieth as beforesaid, half above the Horizon, and moves not, and that is the Polestar; and this star will be the sooner known, because it is more remote from any bright star, than any star near it. The reason why this star moves not is, because it is near the Pole, and the other stars moves round this; yet is not this star without a motion, for it moves round the true Pole, but the eye can scarce perceive it to move at all. An example of this in a night when the stars may be seen: I look up half way into the Heaven, and a little higher, and as near North as I can; which I know by the building of a Church, whose Steeple stands always West from the Church, and there I see a bright star by itself, and it stands so that I may just see it by the edge of a House-wal; then I mark how and where I stood, and go away, and come two, three, four, or five hours after, and stand just in the place as I did before, and find that the star is not removed out of that place; therefore by all tokens this must needs be the Polestar: but if I find the star removed, I conclude that that is not the star, but I try another and another till I do find it; taking this for a sure ground, that it lieth full North from me, and that a little above half of the height of the Heaven, or thereabout, in the Latitude of 51 Degrees. The next thing is, How to know the Meridian in the Heavens. Having found out the North-star, six your eye upon it, and imagine as near as you can, a direct Line to be drawn from that star to the place in the Heaven right over your head, and that Line is the Meridian; and when you see any known star come to this Line, then is that star upon the Meridian; when a star is not quite come to it, that star is said to want of its coming to the Meridian; when a star is gone past this Line, 'tis past the Meridian; and this Line (for so I call it, because all men know not the meaning of an Arch) is an Arch of the true Meridian of the place; and whereas I say let this Line be drawn from the Polestar, it is for the ease of those who are not versed in Astronomy; though the true Arch of the Meridian must be drawn from the true Pole, yet in the use of this Instrument it begets no sensible error to draw this Line or Arch from the Polestar. The next thing is to find the right Ascension of any star in the Rundle. Suppose the outmost edge of any Rundle were divided into 360 parts or Degrees, then must you begin to number at the Meridian-Line that cometh from the Pole to the letter M, which shows March: and so count on, allowing to each space 30 Degrees and that will give you the Right Ascension of the star you desire: As for example. I desire to know the Right Ascension of the bright star in the end of the great Bear's Tail: I begin at M for March, and proceeding I say, 30 and 30 and 30, is ninety: 30 30 30. is ninty more: 180 and 30, is 210, and about five Degrees more: so that I find the right Ascension of this star to be 215 Degrees. The day of the Month, & a star on the Meridian being given, to find the hour of the Night. Bring the star which you see upon the Meridian to the Flower de Luce, and then look for the day of the Month, and right against it you have the hour of the Night given. EXAMPLE, Upon the first of April at night I see the bright star in the middle of the great Bears-Tayl upon the Meridian: therefore I bring it to the Flower de Luce, and looking upon the first day of April I find it is ¼ of an hour past 11. Next, The hour of the Night, with a star upon the Meridian given, to find the day of the Month. Bring the star to the Flower de Luce, and right against the hour of the Night, is the day of the Month. This question may truly be performed, if your Nocturnal be true; and you know the time of Night to three or four Minutes, otherwise you will work false. Lastly, the day of the Month, with the hour to know what star is upon the Meridian. Bring the time of the day, and the day of the month together, and what Star you find upon the line that goes through the middle of the Flower de Luce and the Pole, those are upon the Meridian. And note this, that you are to count your time from the Flower de Luce, 1, 2, 3, 4, and so on to 12 at night, till you come to 12 at noon, where you began; so that the Flower de Luce notes the hour of 12 at Noon, and the rest on in order from Noon to Midnight, and so to Noon again. FINIS.