CO CO o THE ROTATION PERIOD OF THE SUN AS DETERMINED FROM THE MOTIONS OF THE CALCIUM FLOCCULI BY GEORGE E. HALE AND PHILIP FOX PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON THE ROTATION PERIOD OF THE SUN AS DETERMINED FROM THE MOTIONS OF THE CALCIUM FLOCCULI BY GEORGE E. HALE AND PHILIP FOX PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON 1908 CARNEGIE INSTITUTION OF WASHINGTON PUBLICATION No. 93 BALTIMORE, MD., U. S. A. THE ROTATION PERIOD OF THE SUN AS DETERMINED FROM THE MOTIONS OF THE CALCIUM FLOCCULI. The rotation period of the Sun has been determined by three independent methods : ( I ) from measurements of the motions of the spots in longitude ; (2) from measurements of the motions of the faculse in longitude; and (3) from spectroscopic measurements of the motion in the line of sight of the approaching and receding limbs. The first series of monochromatic photo- graphs of the Sun, made with the spectroheliograph of the Kenwood Observa- tory in the years 1892-94, has provided material for a new determination of the rotation period, based upon the motions in longitude of the calcium flocculi. Through a grant from the Carnegie Institution it became possible to undertake the measurement of these plates at the Yerkes Observatory. The results of this investigation are contained in the present paper. THE KENWOOD SPECTROHELIOGRAPH. The spectroheliograph employed in the present investigation is shown in plate i, attached to the eye-end of the Kenwood refractor of 12 inches (30.5 cm.) aperture and 18 feet (5.49 m.) focal length. It consisted of a large grating spectroscope, with collimator and camera of 3.25 inches (8.4 cm.) aperture and 42.5 inches (108 cm.) focal length, inclined to each other at an angle of 25. The collimator and camera objectives were corrected for the K line. A 4-inch (10 cm.) Rowland plane grating, having 14,438 lines to the inch (5,684 lines to the cm.), stood at the intersection of the collimator and camera axes. The spectroheliograph was provided with two movable slits, one at the focus of the collimator (in the focal plane for K light of the Kenwood refractor) , the other in the focus of the camera lens. Both slits, which were 3.25 inches (8.4 cm.) in length, were adjustable in width by means of micrometer screws. They were attached to carriages mounted on steel balls, movable across the axes of the tubes, at right angles to the spectral lines. A photographic plate-holder was supported just beyond the camera slit and, after drawing the slide, the plate-holder could be pushed forward by means of a cam until the surface of the plate almost touched the jaws of the slit. A small 90 reflecting prism was attached to the slit carriage on the side toward the grating, and by a suitable combination of lenses a portion of the spectrum could be viewed without disturbing the plate-holder. This was not used in practice, the K line (in the fourth-order spectrum) being brought on to the slit by observing lines in the green of the overlapping third order with a low-power, positive eye-piece. The motive power was ^^^r>-y /f i <^ i si 2 THE ROTATION PERIOD OF THE SUN AS DETERMINED supplied by a specially designed clepsydra, mounted within the braced frame of the spectroscope. It consisted of a brass cylinder of 3 inches (7.6 cm.) bore and 6 inches (15.2 cm.) stroke, supplied with a three-way valve, per- mitting the liquid to flow in at one end of the cylinder and out at the other. The piston had a cup-shaped leather packing, and the phosphor-bronze piston-rod passed through a stuffing-box in the upper head. At the end of the rod a system of bell-crank levers was attached, which conveyed the motion to the slit at the focus of the camera objective. An extension of the piston-rod passed through a guide in the upper frame of the spectroscope, and connected with the first slit by another lever system. It will be seen that when the piston was set in motion, the two slits would move simul- taneously, and in opposite directions, the first slit across the solar image, the camera slit, containing the K line, across the photographic plate. Water pressure was supplied to the clepsydra from a tank, in which the pressure was kept constant by means of an automatic pump. In winter, alcohol or glycerin was mixed with the water to prevent freezing. 1 This spectroheliograph, though it gave satisfactory photographs of the prominences and flocculi, had one important disadvantage : the distortion of the image resulting from the motion of the slits. In the equation for the plane reflection grating A = (sin 6 sin w) n ^ = angle of diffraction, = i mm., and calculate the values of dO for one side, the center and the other side of the solar image, we obtain the respective values dO = 0.78 mm. (for maximum value of 6) dO = 0.79 mm. (for mean value of 6) dO = 0.80 mm. (for minimum value of 0) In measuring photographs distorted in this way the necessary correction for a point at a given distance from the Sun's limb might be taken from a table, readily constructed for a given position of the Sun's image with respect to the axis of the collimator. To define this position, means were provided for making the solar image concentric with the axis of the collimator. Care was always taken to orient the image so that the distorted axis should be parallel to the solar equator in the photograph. For this purpose the whole instrument could be rotated about the axis of the collimator, the direction of the slit being read off on a position circle. The parallel lines on the photo- graph (due to dust on the slit, which can not be altogether avoided in any form of spectroheliograph when the slit is narrow) were made to serve a useful purpose in the orientation of the image. After a considerable number of distorted photographs had been taken with the instrument, a simple device was attached for the purpose of making the images practically circular in form. This consisted of a lever arm which moved the photographic plate, during the exposure, in a direction opposite to that of the motion of the second slit, and through a distance equal to the difference between the major and minor axes of the distorted image. It will be observed that this correction, though not perfect, is very nearly so. The modified instrument yielded photographs which were very nearly circular in form. 8 The Kenwood spectroheliograph and all the optical parts of the Kenwood refractor were constructed by Brashear, whose valuable services and cordial cooperation greatly facilitated the investigations of the Observatory. Warner & Swasey also gave much useful assistance, in addition to their work of constructing the telescope mounting and dome. During the years 1892-94 there were obtained with the Kenwood spectro- heliograph 2,295 photographs of the Sun showing the calcium flocculi. In 1,408 of these photographs the image was elliptical (or approximately so) *A mechanical device for copying distorted photographs, in such a way as to obtain a circular image, was also constructed at the Kenwood Observatory. THE ROTATION PERIOD OF THE SUN AS DETERMINED in form. These were obtained before the device for correcting the distortion of the image had been applied to the spectroheliograph. By means of the apparatus devised for the purpose, these negatives might have been copied in such a way as to give circular images, in which case they would have been available for the present investigation. But in view of the much greater excellence of the photographs which were being obtained with the 4O-inch Yerkes Observatory telescope, when the present reduction of the Kenwood plates was undertaken, it was decided to confine the work to the measurement of the circular images, 887 of which were available. Mention has not yet been made of the slight distortion of the Sun's image, caused by the curvature of the spectrum lines in the Kenwood spectroheliograph. 4 Since the motion of the photographic plate, which served to transform the elliptical image into a nearly circular one, did not also furnish the means of correcting for the curvature of the slit, precautions had to be taken, while making the photo- graphs, to eliminate the effect of this curvature. For this reason, the plates were made in two series, in one of which the slits were made parallel to the Sun's axis, while in the other they were placed in a position angle 90 from this. For the present investigation the plates of the first series were employed, since the displacement (due to curvature) of the flocculi in longi- tude would be, in this case, only a second-order effect, too small to be appreciable in photographs no sharper than those available. In order to avoid errors in the identification of the flocculi measured, no attempt was made to employ plates separated by two or more cloudy days. The best plate, corresponding to each day in a series of two or more clear days, was selected for measurement. In this way the number of plates to be measured was reduced to 138, covering the period 1893 July 31 to 1894 September 29. * Radius of curvature = about I m. Condensing Plate ia"lens Globe FIG. i. PLAN AND ELEVATION OF THE GLOBE MEASURING MACH FROM THE MOTIONS OF THE CALCIUM FLOCCULI. METHOD OF MEASUREMENT. Two causes made it undesirable to adopt the ordinary method of measure- ment in the reduction of these photographs. In the first place, the high degree of precision attainable in measuring very sharp direct photographs of the Sun, such as those comprised in the Greenwich series, is out of reach in the case of photographs taken with such an instrument as the Kenwood spectroheliograph. In the second place, the measurement and reduction by the ordinary process of the numerous positions required would have been a larger task than could be undertaken in the intervals of work with the Rumford spectroheliograph. Accordingly a new method of measurement was devised by Mr. Hale, which is at once exceedingly rapid in execution and, at the same time, sufficiently precise for the immediate object in view. 5 The photographs are projected by means of the light of an electric arc lamp upon a globe accurately ruled with a series of meridians and parallels. The details of the arrangement are described below. The greater part of the apparatus was constructed in the instrument shop of the Yerkes Observatory (see fig. i). References to this apparatus will be used as follows : A = Arc lamp, fed by clock-work so as to keep the arc at a fixed point. C = Condensing lens, 10 inches (25.4 cm.) in diameter. P = Plate-holder, which carries the solar negative. L = 12-inch (30.5 cm.) objective of 18 feet (5.49 m.) focal length, which forms an image of the photograph upon the globe, G. M = Plane mirror inserted in the path of the rays, to secure the neces- sary distance of the globe from the lens, in the limited space available. The globe must subtend an angle of 32' as seen from the lens. THE GLOBE. The globe is of cast-iron, accurately turned to form a sphere 9.53 inches (24.21 cm.) in diameter. It was enameled white to receive the ruling, and afterwards reworked to a spherical form. In order to rule the parallels of latitude, centers were drilled at points corresponding to the north and south poles, and the globe was mounted in a Brown & Sharpe milling machine, between the spindle and the overhanging arm. A support for a ruling-pen was clamped to the spiral head, the pen resting on the globe. The position of the equator was determined by 5 For an improved form of globe-measuring machine (the Heliomicrometer), capable of giving results of the highest precision, see Contributions from the Solar Observa- tory, No. 16 ; Astrophysical Journal, June, 1907. Plane mirror 6 THE ROTATION PERIOD OF THE SUN AS DETERMINED careful measurement and ruled by rotating the globe. The support carrying the pen was then moved through i by means of the index plate, and the parallel was drawn by again rotating the globe. After the parallels to 60 north and south had been ruled in this way, those at 5, 10, 15, etc., were slightly strengthened; the parallels marking the 10 zones, viz.: 10, 20, 30, etc., were still further strengthened to facilitate the readings. To rule the meridians, the globe was mounted on the cross-table of the milling machine, with the centers again at the poles, and was clamped to the spiral head, so that it might be rotated through any desired angle by means of the index plate. The pen was mounted on an arm, permitting it to be moved in a great circle from pole to pole. The first line ruled, which we shall subsequently call the central meridian, was carefully located midway between the centers on which the globe was ultimately to rest. These had been drilled at points on the globe exactly 90 from the poles. Hence, this axis passes through the globe as a diameter in the equatorial plane. After the principal meridian had been ruled, by moving the pen from pole to pole, the other meridians were successively ruled at i intervals, accurately determined by means of the index plate. As in the case of the parallels of latitude, the meridians marking the multiples of 5 in longitude were strength- ened, and those at 10, 20, 30, etc., were made still heavier. The ruled globe was mounted as shown in plate 2. When supported in this way, any motion of rotation, producing a change in the inclination of the globe's axis, corresponds to a change in the inclination of the Sun's axis with reference to the ecliptic. With the aid of an index moving over a divided arc, the globe may be set so that the heliographic latitude of the center of the globe corresponds to that of the Sun's center on the day when the photograph to be measured was taken. The globe and support can be moved on rails toward or from the pro- jecting lens, so that the varying diameter of the solar image, at different seasons, can be made to correspond with the diameter of the globe. The entire apparatus rests on a strong shelf, supported on brackets from a brick wall in the basement of the Yerkes Observatory. PLATE-HOLDER. The plate-holder, fig. 2, is provided with spring clips for holding the plate firmly in position. The disk which carries the plate may be rotated in a plane perpendicular to the beam of light, the orientation of the plate being read on a divided arc. The Kenwood spectroheliograph could be rotated so that the motion of the slits in the instrument was parallel to the Sun's axis for the date on which the photograph was made. With this adjustment of the instrument, which was always made for plates of the first series, a line drawn upon the plate by a needle crossing the first slit may always be taken to correspond with the direction of the Sun's axis. By clamping the plate in FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 7 the holder, so that the line corresponds with the zero of the scale, the position- angle of the Sun's axis is accounted for. 8 The plate-holder is mounted in a fixed position on a shelf just behind and above the globe, and has no motion in the direction of the beam. Two motions are provided for centering the image on the globe. The east and west setting is accomplished by moving the plate-holder toward or away from the wall, while the north and south motion is produced by raising or lowering the plate-holder in its supporting frame by means of a double wedge. The centering of the image is done on a fixed screen, mounted in front of the globe, as shown in plate 2. The FIG. 2. THE PLATE-HOLDER. position of the plate-holder is such that it may be adjusted by the operator while he is observing the globe, thus rendering the centering a simple matter. The operation of mounting the plate in the plate-holder, the setting of the globe and the orientation of the image, occupies from 5 to 10 minutes. PROJECTING LENS. The lens L, which is used to form an image of the plate on the globe, is a 12-inch (30.5 cm.) photographic objective, of 18 feet (5.49 m.) focal length, which was formerly used with the Kenwood telescope. The position of the 6 The Rumford spectroheliograph can not be rotated; but the dust-lines show the direction of the plate's motion (north and south). In measuring photographs made with this instrument, the plates are clamped with the dust-lines parallel to the zero line on the disk, after which the disk is rotated through an angle equal to the position- angle of the Sun's axis, for the day on which the plate was taken. 8 THE ROTATION PERIOD OF THE SUN AS DETERMINED lens, between the plate-holder and the globe, is necessarily dependent upon the position of the globe itself. Since the globe must be moved to correspond with the change in diameter of the solar image, the lens is correspondingly moved by an amount such as to retain the plate and globe in the conjugate foci of the lens. Theoretically, the angular diameter of the globe, as seen from the lens, should be the same as the angular diameter of the Sun as seen from the Earth. 7 This would place the globe at a distance of about 84.26 feet (25.68 m.) from the projecting lens. Since the diameter of the image on the Kenwood plates is 2 inches (50.8 mm.), when the angular diameter of the Sun is 32', the lens should have a focal length of about 14.84 feet (4.51 m.), in order that the projected image may correspond in diameter with the globe. No lens of this focal length, and of sufficiently large aperture, was available, and accordingly the 1 2-inch objective was employed. As the distance of the globe from this lens was 103.8 feet (31.64 m.), a small error enters into the measurements. In the triangle, Sun's center, flocculus, Earth, we have intro- duced an error in the angle at the Earth usually designated s r or p. This angle / enters into the solution of the solar triangle, pole, flocculus, center of the disk, as a correction in the arc, flocculus, center of the disk, usually called ^ or p, and at the limb, has its maximum value of 16'. In our case $1 is smaller, having a maximum value of 13.1'. That is, every point would appear to be slightly shifted toward the center of the globe. Even in the case of the maximum difference the error is inappreciable. In order to avoid the errors always incident to measures of objects lying near the limb in solar photographs, the measures of the present series of plates have been confined to regions lying within 45 of the central meridian. On account of the rarity of occurrence of large flocculi in high heliographic latitudes, it was unnecessary to set a limit in the direction north and south. In the extreme cases, where the measured position is 45 east or west of the central meridian, and 45 north or south, the difference between the true s' and our erroneous value is s' s^' = 2.4'. Had this difference been appreciable, it might have been eliminated for the region in which the measures are confined by slightly enlarging the circle on the screen in front of the globe, with which the image is always made to coincide. ARC AND CONDENSING LENS. The arc and condensing lens are inclosed in a small room, in order that the general illumination on the globe may be minimized. As already remarked, the arc is of the focusing type, with inclined carbons. The condenser is a plano-convex lens, 10 inches in diameter. 7 The theory of the globe-measuring machine will be published in a subsequent paper. PLATE 2. FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 9 ADJUSTMENTS. The principal adjustments are as follows : (1) The plate should be normal to the line joining center of globe and center of plate. (2) The 12-inch projecting lens should be collimated in this line. (3) The rails on which the globe slides should be parallel to this line. (4) The axis of the globe must be adjusted in azimuth (perpendicular to the line of collimation) and leveled so that a straight perpendicular line on the plate can, in projection, be made to coincide with the central meridian. (5) When the globe is so adjusted, through rotation on its axis, that a horizontal line on the plate, in projection on the globe, coincides with the equator, the index which gives the inclination of the Sun's axis must read zero. PROCESS OF MEASUREMENT. The operations to be carried out in measuring a plate are as follows : The plate is mounted in the plate-holder, so that the line parallel to the solar axis corresponds approximately with the zero of the scale. The arc is started, and the accurate adjustment for position-angle is made by rotating the plate until the projected line coincides with the central meridian of the globe. The axis of the globe is then inclined so as to make the heliographic latitude of the center of the disk correspond with that of the center of the Sun's disk on the day in question. The image is then centered in the circle on the screen, the globe is moved until the image falls exactly within the circle, and the projecting lens is moved, if necessary, to preserve the focus. In measur- ing the flocculi the image is received upon a small white card, from which it is dropped upon the globe by rapidly moving the card aside. As the card is free from the lines ruled on the globe, the image can be seen upon it to better advantage. The positions of the points in heliographic latitude and longitude from the central meridian are read off directly, by estimation, to the nearest tenth of a degree. The identification of points to be measured requires much care, in view of the complexity of the changes of form of the flocculi. Prints from the original negatives were made on " Velox " paper, and all measured points were carefully marked. By comparison of the prints, the points can be followed from day to day, thus assuring certain identification. The flocculi change in form rather rapidly, but a number of points were followed for four, five, and six days. Of the 1,213 points measured, 647 correspond to inter- vals of one day; 331, to two days; 137, to three days; 65, to four days; 26, to five days ; and 7, to six days. The positions of all points were estimated to a tenth of a degree. 10 THE ROTATION PERIOD OF THE SUN AS DETERMINED SOURCES OF ERROR. In considering the many sources of error that may affect our results, the character of the photographs must always be borne in mind. The small size of the solar image; the lack of sharpness of the flocculi ; and their rapid changes of form, making identification of points for measurement very diffi- cult, all tend to reduce the accuracy of the results. As compared with such investigations as those of Stratonoff on the motion of the faculse, however, we have two important advantages which reduce, if they do not completely offset, the disadvantages arising from the above causes. These include : (1) The possibility of making all measures near the center of the disk, instead of near the limb. (2) The greater number of objects available for measurement, and the consequent better distribution of the points in latitude. 8 The following sources of error must be considered : (1) Distortion of the solar image, arising from (a) The different rates of motion of the first and second slits (p. 3). This is corrected, with sufficient exactness for the present work, by the motion of the photographic plate during the exposure. (b) Errors in centering the solar image on the first slit. It is evident from the equation of the grating that the degree of the distortion of the image depends on its position with respect to the axis of the collimator. For any slight deviations of the solar image from the central position, however, the effect is small, and much less than that due to (a). (c) Curvature of the second slit. When taking the photographs, the effect of curvature was reduced to an inappreciable quantity of the second order by setting the slit in all cases parallel to the solar equator. The latitudes are thus mainly (though but slightly) affected, while the longitudes suffer only in the second order. (2) Errors of globe divisions. These were found on examination to be so small that they could safely be neglected. (3) Care was always taken in the orientation of the image and in centering it on the globe. The accidental errors arising from these sources were undoubt- edly small. (4) The focal length of the only lens of sufficient aperture available for the projec- tion of the solar photograph on the globe was 18 feet (5.49 m.) instead of 14.8 feet (4.51 m.), required by theory. The errors due to this cause have been shown to be inappreciable. 8 This applies particularly to well-defined images, in which the minute flocculi are shown. FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 11 ROTATION PERIODS DERIVED FROM THE MEASURES. About 3,000 measures were obtained, of 1,213 points in the flocculi. The actual heliographic longitudes of the flocculi were not measured, but only their differences in longitude east or west of the central meridian. The lati- tudes of all the points were measured ; but they are, of course, affected by the slight error due to curvature of the second slit. This does not exceed 0.6 in the extreme case and affects only the grouping of the different flocculi into zones in taking the mean value for each zone. As the spectroheliograph was sometimes oriented with the convex side of the curved second slit north and sometimes with the convex side south the error of grouping will be practically self-compensating. In gathering together the different measures of the same point, to determine the rotation period, the first reading was taken as zero degrees, and the others reduced accordingly. The readings thus assembled are given in table i. It has not seemed necessary to publish all the measures from the original note-book. The plate number and date are given in the first column. The second column contains the flocculus number, as marked on the enlarged prints for the purpose of identification. The third column gives the zone in which the flocculus was found: a = o to 5 ; b = o to 5 ; c = 5 to io;d = 5 to 10 ; e = 10 to 15 ; / = 10 to 15 ; g = 15 to 20 ; h = 15 to 20, etc. The sixth, seventh, eighth, ninth, tenth, and eleventh columns show the movement in longitude during the days, or portions of days, intervening between the first and second plates, first and third, first and fourth, etc., of the flocculus in question. The fourth column gives the angular movement per day, as derived graphically from the readings, by platting the times as abscissae, and the difference in longitude as ordinates. The rise of the line which best represents the observations, during an interval of 24 hours, is the desired angular movement. The cross-section paper employed, for which we are indebted to Mr. Abbot, was specially ruled with great accuracy for the Smithsonian Astrophysical Observatory. The paper is ruled in millimeters, and the scale of platting is such that 5 mm. correspond to i hour in the abscissae, and single milli- meters to o.i in the ordinates. Heavy lines were ruled to correspond with the even 24 hours, and these were taken to represent the noon hour. The times of the plates were laid off, so many hours and minutes, right or left from this line, depending upon whether the plate was taken in the afternoon or forenoon. The first ordinate was o, the second approximately 13, etc., as given in columns 6, 7, 8, 9, 10, and n. 9 Let y 19 y 2 , y 3 , . . . . represent the observed motions in longitude, corre- sponding to the times f , t 2 , f a , . . . . In general t it t 2 , t 3 , . . . . are not 9 The graphical method described below is due to Dr. Frank Schlesinger. 12 THE ROTATION PERIOD OF THE SUN AS DETERMINED exact multiples of 24 hours. In the case where we have three observations connect y and y 3 , and let A and A 3 represent the values of the longitude corresponding to the intersections of this line with the noon lines of the first and third days. Similarly A 2 is given by the intersection of the line joining y and y 2 with the noon line of the second day. In the case of four observations, the values of A , A 2 , A 3 , A 4 are given by the intersections with the corresponding noon hours of the lines joining y and y 4 , and y 2 and y 3 . Treat A 1? A 2 , A 3 , .... as observed quantities, and call A the value of the longitude corresponding to zero time. By the method of least squares, the equations A A! = o A + x A 2 = o A + 2.x A 3 = o give at once 3*0 + 3* (AI + A 2 + A 3 ) = o 3A + 5* (A 2 + 2A 3 ) = o whence Thus, in the case of observations made on three successive days, the position of the middle point does not affect the result; for in approaching the thread (which was used in place of drawing lines) to the middle observa- tion, the inclination is not changed. This is, of course, absolutely true only when the intervals are accurately equal to 24 hours, but it is a sufficiently close approximation in our observations. The error does not exceed 0.05 under ordinary conditions and 0.1 in a few extreme cases. For four consecutive days we obtain The second form here, as in the following cases, gives the weight assigned to the line through the extreme observations and to that through the inter- mediate ones. In case the second day's observation is lacking r-- 2 (\ \ ^ l f\ \ \ l $* / A 4 A^ A 3 A (A.-AJ --(A, -A,) =-|6(^ ) + If the third day's observation is lacking 4 A A A 4 A 2 (\ \ \ _\ I (\ \ \ __ I -? (x < H-(*.-A.) -7 2 For five consecutive observations the middle one disappears, as in the case of three, and we find A 4 A 2 FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 13 With A 2 or A 4 missing, the solutions are similar, but too complex to be of value in platting. If A 2 and A 3 are lacking, we find If A 3 and A 4 are lacking Fig. 3 illustrates the graphical solution of the observations of Flocculus No. 737. The observations were made on plates No. 3106, 1894, Mar. 14, i h 59 m ; No. 3112, 1894, Mar. 15, i h i2 m ; No, 3117, 1894, Mar. 16, 2 h 44 m ; and No. 3121, 1894, Mar. 17, I2 h 04 m . 7i =0 y 2 = 12.7 y 3 = 26.2 y 4 = 38.7 A! = 1.10 A 2 = 12.07 ^3 = 24.76 A 4 = 38.68 x = ^ (A 4 A,) + -L (A 3 A 2 ) = 13.203 Or, extending the line A 2 A 3 for the three days, it intersects the noon lines on the first and fourth days at a and (3. Now, knowing that the line A X A 4 has nine times the weight of A 2 A 3 , we may make a reading on A a one-tenth the distance from A toward a = 1.05 and on A 4 /? one-tenth the distance from A 4 toward (3 = 38.56 1.05 -^=13.203 o Or, as is most frequently done in practice, we may draw a third line A^ parallel to A 2 A 3 passing through A 1 . Again read on A 4 8 one-tenth the distance from A 4 toward 8 = 38.50 38.50+ 1. 10 *:= -=13.200 o In case we use the general formula and express ^, t 2 , t s , t 4 , in minutes, _ T * *- k = the number of observations, in this case 4, we find x 13.183 14 THE ROTATION PERIOD OF THE SUN AS DETERMINED 30 2-5 20 15 10 30 25 20 15 10 FIG. 3. GRAPHICAL INTERPOLATION METHOD. FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 15 TABLE i. Diurnal Motions of the Flocculi. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. i 2 3 4 5 6 No. 2401 I C 14-74 I3.78 12.6 26.6 39-9 1893, July 31 19 C 14.84 13-88 11.7 25-9 39-7 2*127111 5 e 14.03 13.07 10.6 24.6 5' e 14.42 13-47 10.8 25.0 38.5 4' e 14.38 13.42 10.8 18 f 14.26 13.31 10. 1 25.1 23 g 14.06 13.10 10.7 24.3 37-4 5i.o 2' e 14.42 13.47 10.9 24.5 38.2 52.5 14 h I3./8 12.82 10.3 15 h 13.89 12.93 10. 1 24.3 ii j 12.67 11.72 9.4 V k 13.64 12.68 27.7 36 i 8' I I J-O.VMt 12. 6l 12. 6l 11.65 11.66 9.9 9.3 -**o *o 21.6 o v- 16 I 13.54 12.58 9.9 23.7 16' I 13.19 12.23 9.8 23.1 No. 2407 i' c 14.62 13.67 13.6 27.0 41.8 1893, Aug. i 27 d 14.42 13.47 14.0 27.2 41.0 Q h 34 m 26' f 14.41 13.45 14.5 26 h 12.54 11.58 12. 1 3 i 14.59 13.64 14.2 27.3 42.0 6 i 14.29 13-33 I4.I 27.3 22 j 12.07 ii. ii 13.8 26.7 40.3 6' k 14.07 13.12 13.7 26.0 No. 2421 32 b 13.99 13.04 12.6 1893, Aug. 2 _ ./ b 14.72 13.76 13.6 27.3 n h 30 m 38 b 15.24 14.29 13.8 36' b 13.81 12.85 12.5 25.5 36" b 14.26 13-30 13-7 26.4 37' c 14.37 13-41 13.3 26.6 39.7 36 d 14.62 13.66 13.6 27.1 33 e 14.78 13.82 12.8 27.4 4 i 14.71 13-75 13.2 27.3 29 i 14.49 13.54 12.9 26.9 30 i 14.06 13.10 12.7 26.0 No. 2429 35 d 15.87 14.92 15.4 30.1 48.7 1893, Aug. 3 47' h 14.22 13.26 13.3 26.7 43.4 5L9 I0 h 42 m 30' i 14.66 13.70 13.9 29' i 14.66 13.70 13.9 47 j 13.71 12.75 13.1 25.8 43.9 38' 38" I I 13.09 14.35 12.13 13-39 12.3 13.6 44-4 53-4 66.7 No. 2442 38'" b 14.57 13.62 13.3 1893, Aug. 4 52 b 14.75 13-79 13.9 31-7 40.9 54-5 69.2 n h 7 m 53' b 14.73 13-77 13.5 55 b 14.68 13.72 13.8 3L5 40.7 54-1 69.0 5i d 14.69 13.73 14.2 31.2 40.8 54-2 69.4 5i' d 14.93 13-97 13.3 31-7 40.8 23' e 14.15 13-19 12.9 42 e 14.73 13.77 13.5 42' e 14.19 13.24 12.6 29.8 44 e 13.69 12.73 13.0 28.8 38.2 16 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 5 6 No. 2442 Confd. 44' e 14.41 I3.45 13.5 30.5 46 g 14.15 13.19 13-0 29.1 39-0 52.6 49 h 14.64 13-68 14.2 3L5 40-7 45 j 14.10 13.14 13.0 30.4 39-0 45" I 14.62 13.67 13-4 No. 2452 5/ d 14.78 13.83 I7.I 1893, Aug. 5 56' e 13-93 12.97 16.5 10^341x1 54 f 14-57 I3.6l 17.3 27.0 40-3 54-9 58' g 15-47 14.51 l8. 5 47" h 13.29 12.33 15.6 24.6 62 h 14.66 13.70 I 7 .6 26.8 40.2 55-8 59 j 13.63 12.67 I7.I 25.6 38.3 59' j I4.0O 13.04 17.4 26.0 No. 2465 7i e 14.58 13.62 9.8 1893, Aug. 6 78' e 14.71 13-75 9-8 23.3 5 h IO m 60 61 f f 14.01 14.14 13.06 I3.I8 9-5 9-3 22.9 22.3 as 48.0 64' f 13.97 13.01 9-3 79 f 13.74 12.78 8.7 21.7 70 g 14.58 13.63 9.8 77 14.58 13.62 9-8 62' 13.65 12.69 9.1 79' h 14.11 13.15 9.1 22.3 So h 14.17 13.21 9.1 22.4 63' j 13.93 12.97 8-9 22.0 65 j 14.07 13.11 9.1 22.2 36.2 69 j 13.40 12.44 8.7 20.6 34.5 74 j 14.66 13.70 8.8 22.3 37.9 6/ I 14-39 13.43 8.5 22.4 37.0 48.3 64 n 14.26 13.30 9-5 22.7 36.7 68 jpr 14.26 I7.7Q 22.8 36.6 No. 2471 49' & h *.J,rV/ 14.74 A O O v 13.78 13.6 28.0 1893, Aug. 7 50 d 15.08 14.12 13.5 28.8 I0 h 27 m 66' j 14-43 13.47 13.7 27.5 80' j 14.03 13.07 12.8 75 d 14.03 13.07 13-0 26.7 78 c 14-33 13.38 12.9 27-3 83 p 13.97 13.01 12.6 26.9 ^s.i 64.1 84 Q e 15.27 14.31 12.9 * -7 28.0 O*-** J- 42.4 80" h 13.56 12. 60 12.3 69' j I4.I8 13.22 12.9 No. 2482 82 c 15.13 14.17 15.1 1893, Aug. 8 77' g 14.37 13.41 14.2 26.6 gh^m 64" n 13.91 12.95 13.8 89 K I3.8I 12.85 13.3 25o 00 pr 13.88 I2.Q2 n 8 2^ 4 Cj 2 V 92 f *O'"" 14.67 J "*' y* 1 13.71 J.^} .U 13.7 ^.J 'T 1 27.2 O A ** 04 ; 14.12 1^.16 14 O 2^ Q 52.0 J7*T Q5 y ; A *T ' X 14.08 A O * * w IT.. 12 L^.\J 13.8 ^o *y 2^ Q 3** ** 51.8 96 j i 14.33 x o x 13.37 A O *-' 14.0 *O 'V 26.7 O * 52.0 97 i 13.91 12. 95 j.^|..vy 17.7 ;: ' 26.0 } * :? 78.6 96' y /' 14.42 J- 13.46 *o* / 14.2 26.2 53.2 j FROM THE MOTIONS OF THE CALCIUM FLOCCULI. TABLE i. Diurnal Motions of the Flocculi. Continued. 17 Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. 1 2 3 4 5 6 No. 2496 1893, Aug. 9 I lh26 m 98 99 106 101 a f a g I4.67 14.67 14.62 I3.8l 13-71 I3 'S 13.66 12.8=5 12.6 12.6 12.3 1 1. 6 38. 4 77 I 67.7 106' 104 c a 14.40 13.56 13.44 12.60 12.3 10.4 36.3 K>8' 9i 93 97' 83' 90' g a f j i i 13-55 14.06 13.65 13.97 13.65 13.80 12-59 13.10 12.69 13.01 12.69 12.84 12.6 12.0 11.6 11.9 ii. 6 12. 33-0 77 n 62.8 90" 103 i f 13.87 13.97 12.91 13.01 11.8 11.9 JQ.O No. 2501 1893, Aug. 10 102 IO7 j a 14.00 I3.8O 13.04 12.84 24.8 25.7. 53-1 9 h 23 m 87 b 14.66 17.70 27.0 T08 P I -i 42 '" 12 46 */*; 24 6 No. 2521 118 118' 109 A t g (i 13.62 13.57 14. 52 12.66 12. 6l 17. C^ 2 4 .2 25-6 28 5 52.0 5L3 80.0 1893, Aug. 12 no i I4.I8 13.22 28 I 57 2 8^47" III P 14 40 T7 44 28 2 112 n 80 12 QT, 27 2 III n 80 12 QT. 27 2 114 ft 14 10 17 14 */'~ 27 6 IIC i 14.04 1 3. 08 89' i 14.57 1J.WO 17. OI 28 7 12?' i 14.25 1 7. 2O 28 o 102' j f~o M.6o 17.72 28 o 108" g 1C. 27 14.71 T.O.I No. 2542 116 f 14.11 13.15 1891, Aug. 14 124 y Mid it 18 o 2 ^8 Q 52 2 65 Q Ijhcm 133 y 14 31 17 7C 20 7 40 I 52 8 132 c 13.70 12 74 28 I 77 Q 50 4 63.1 135 i 17. QI 12. Q^ 28 7 38 7 No. 2558 1893, Aug. 16 4 hoom 129 137 138 e i rf I4.IO 14.57 14 58 13.14 13.61 17 62 10. 1 10.2 10 6 22.7 24 35.9 77 Q 66 9 70 3 No. 2560 1893, Aug. 17 141 139 136 140 143 150 150' 134 142 ICJ f i h i I h g f n 14.40 14.24 14-37 13.31 14.21 13.84 14.54 14.29 14.63 13 06 13.44 13.27 13.41 12.35 13.25 12.87 13.57 13.32 13.66 13 oo 9-7 9-9 IO.O 9-3 9-9 IO.O 9-7 IO.O 13.5 12 8 22.8 23.1 23.3 21.0 22.4 23-4 26 o o/.y 36.6 34.1 54 5 62 6 io h 38 m 152 IC7 I n 13.10 14 10 1 12.14 17 14 12.0 ii 8 26.0 55.0 18 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 5 6 No. 256oCont'd. 157 n 14.96 14.00 I3-I 27.6 156 h 15.84 14.87 13.6 29.3 155 h 14.25 13.29 12.0 26.2 163 f 14.55 I2.O 28.9 57.1 60.0 150" h **T*Oil 13-23 12.26 x ' y 12. 1 o/ * ^-'y y 160' j 13.94 12.97 12.8 No. 2569 145 f 12.78 12.81 12.5 1893, Aug. 18 1 60 j 13.24 13.28 42.6 164' j 14 4 45-0 j 14.64 13^68 14 5 43-8 C7 7 1 68' d 14.75 151 44 ^ o/ o C7 c 140' i 14.76 13.80 13-5 HH*O o / * o 171 I 13.09 I4.I 41.8 54.0 171' I 15.30 14.34 14.0 OH* -7 165' d 14.52 14. 1 43.5 No. 2580 x w ,j A H*O ' **! * HO *O 1893, Aug. 19 No. 2588 194 I 14.48 13.51 13.0 1893, Aug. 21 165 d 14.06 13.10 12.6 3 h I3 m 170 n 13.23 12.26 n.8 174 h 15.11 14.15 13.6 175 h 13.86 12.90 12.4 176 h 14.15 13.19 12.7 180 j 13-86 12.90 12.4 181 k 13.55 12.59 12. 1 183 c 13-55 12.59 12. 1 184 c 15-45 14.49 13-9 185 e 13.99 13.02 12-5 186 I 13.60 12.64 12.2 187 j 14.48 13.51 13-0 188 189 j j 13.55 14.06 12.59 13.10 12. 1 12.6 190 j 13.73 12.77 12.3 191 f 14.36 13.40 12.9 197 m 13.55 12.59 12. 1 195 k 13.33 12.36 11.9 196 k 13.46 12.50 12.0 No. 2590 1893, Aug. 22 2^25 No. 2598 199 k 13.36 12.39 15-0 1893, Aug. 28 200 k 13.07 12. II I5-I 24.1 38.0 lOh^Qm 206 i 13.93 12.96 16.0 25.9 40.6 208 g 14.40 13.43 16.2 209 m 13.82 12.85 15.5 211 h 14.40 13-43 16.2 212 h 14.50 13.53 16.3 213 k 13.49 12.52 15.1 214 i 14.44 13.47 16.4 26.9 42.1 215 i 14.25 13.28 16.3 26.3 41.7 217 b 15-12 14.15 17.1 2I 9 h 14.21 13.24 16.2 27.1 FROM THE MOTIONS OF THE CALCIUM FLOCCULI. TABLE i. Diurnal Motions of the Flocculi. Continued. 19 Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 5 6 No. 2617 1893, Aug. 29 4 h 03 m 220 221 222 223 k k k e i h 13-37 13-09 12. 80 14-63 14.23 14 2$ 12.40 12.12 H.83 13-66 13.26 13 28 9.6 9-7 10. 1 11. 7 10.3 II 23-4 22.8 22.3 25-8 25.1 24 7 36 8 40 4 77 No. 2619 1893, Aug. 30 I2 ho3 m 225 228 230 231 232 237 b d b i d f+h s 13-88 14.46 12.37 15.65 14.72 14.36 14.72 I4.I8 12.91 13.49 11.40 14.68 13-75 13-39 13.75 13.21 13-6 14.2 12.5 15.5 14.6 14.4 14-5 13.5 22.1 26.6 26.0 26.7 25.8 39.8 65? 238 i 14 10 13.22 14.3 2^.0 ^ 0^.2 No. 2628 1893, Aug. 31 lh 2 8 m 240 242 233 241 239 246 8 d e f /' 14.87 14.48 14.82 14.77 14.74 14.78 14 dt 13.90 13.51 13.85 13.80 13-77 13-81 13.46 15-3 13.7 14.6 12.2 12. 1 12.3 II. I 27.0 25.7 25.0 25.3 23.9 39-0 "52.1 247 248 249 250 251 h f 14.49 14.96 12.98 13.96 14.77 13.52 13.99 12.01 12.99 13.36 II. I II. 10.6 14.8 11.7 24.5 24.0 23-8 24.5 50.4 50.6 75-9 252 2^3 e g 14.61 14 i e 13.64 13. 18 12.0 12. 1 24.7 24.7 51.0 254 $ s , h 13-73 14.29 13.84 J.J.XW 12.76 13.32 12.87 II. I II. 2 9.7 23.1 24.2 22.4 49-7 No. 2634 1893, Sept. i io h 4i m 257 258 259 260 26l 262 263 264 % 267 h d d f d h i { 14.94 14.87 14.42 I5.32 15-03 15.79 15.32 15.18 14.06 I5-7I 14 DO 13.97 13.90 13.45 14.35 14.06 14.82 14.35 14.21 13.09 14.74 n 72 13.2 I3-I 12.7 13-5 13-3 14.0 13-5 13.4 12.4 13.9 1^ 40 O 268 g 14 7Q 13 82 It 41 2 269 27O ; j 13-86 14 32 12.89 13. 3^ 12.2 13.2 30.8 No 2639 271 244' { cr 13-86 13 68 12.89 12 71 12.2 2=; 8 1893, Sept. 2 phjgm 273 275 2?6 s t h 14.01 13-66 14 08 13.04 12.69 13. II 26.0 31 52.5 Si.J 53.6 68.2 278 1 14.10 13.22 20. Q 20 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 5 6 No 2639 Con? d 27Q f 14 S2 13 SS 27.=; */y 280 i, 14 08 13 II as:i C4 4 69.3 281 or 13 72 12 7^ 2=5.7 3 ^*7 CQ O "y-o 6s. s No 2651 274 ; 14 67 13.70 27.2 1803 Scot 4 283 i 14.42 13.4^ 27.0 41.6 IO^I2 m * ^7 13.03 12.66 ' ;: 2=;. 6 30.2 288 m 14. S7 13. 60 -^j.w 26.0 200 h 14. q8 J.J.V./W 13.61 27.0 201 ?, M.C7 X O .V/i I3.6O ' 26.0 2Q2 f, 14. S8 J.J.V./W 13.61 27.0 203 I 14.98 14.01 27.8 204 \ 14.73 J.tf.Vi 13.76 27.3 207 f 14.69 13.72 27.9 42.4 208 J f 13 01 28 o 43 O 301 J or 14 38 13 41 27 42 7 qe Q 302 fl 14 S7 13 60 '' 2O 3O4 d+f Ai f.O/ 13 62 i^).W 12 6^ 27.7 30 I 305 f 14.42 1^ 4C 27.4 oy.i 41 O 306 or 14.13 1^.16 2=5.7 40 7 No. 2675 1893, Sept. 6 9 h 47 m No. 2681 310 311 314 315 3l6 319 320 326 289 h { b d g S f g 14.02 13.84 14.41 15.84 14.12 14.67 15-21 13-74 14.12 13.05 12.87 13-44 14.87 13-15 13.70 14.24 12.77 13. 1 1 ? 14.4 14.2 14.8 16.4 14.5 I5-I 15.7 I4.I ic.-z ^3.0 1803, Sept. 7 320 h 14.00 13.12 14.0 C2.Q I2 hjgm 330 331 { **f w Jj 15.26 14.04 14.29 13.07 15.4 IS. I =52.7 332 333 334 $ III 330 i k k i i g or 14.64 14.92 14-07 13.14 14.07 13.56 14.34 14.28 *O-"/ 13.67 13-95 13.10 12.17 13-10 12.59 13.37 13 31 14.7 15.0 I4.I I3.I I4.I 13.5 14.4 14 6 ^3.7 No. 2694 340 744 * I e 12.94 14.06 11.97 13.00 12.9 38 5 1893, Sept. 8 34 c h 13.66 ' x o-"y 12. 60 VJ ^ 2 h I2 m 346 h XJ.VW 14.06 13.00 38 s 347 d *t pv ~ 14.06 13.00 38 =5 No. 2699 3S3 f 14.26 13.20 40 I ^2.2 1893, Sept. ii 354 f 14.61 i^.^y I3.O4 40.3 I2 h 48 m 355 f 14.52 17. CC 40 356 d 15.19 M.22 ~ 42 o 357 d 14.13 I3.l6 38.8 S3. 2 358 d 14.16 13.10 38.5 S3. 1 360 f 14.44 13.47 30.8 FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 21 TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. i 2 3 4 5 6 No. 2712 361 b 14.30 13.32 13.9 1893, Sept. 14 362 d 14.30 13.32 13.9 363 d 14.20 13-22 13-8 364 d 14.39 13.41 14.0 365 d 13.69 12.71 13.3 % f f 14.39 13.15 13.41 12.17 14.0 12.7 372 f 14-77 13.79 14.4 373 f 15.17 14.19 14.8 374 f. 14.67 13.69 14.3 375 i I3.8I 12.83 13.4 376 i 14.59 I3.6l 14.2 377 i 14.59 I3.6l 14.2 380 g 13.15 12.17 12.7 c 15.84 14.86 15-5 382 c 14.30 13.32 13.9 383 i 14.67 13.69 14.3 i I3.8I 12.83 13.4 386 c 13.69 12.71 13.3 387 d 13.52 12.54 13.1 388 I H.53 10.55 II.O 389 i 13.90 12.92 13.5 39i h 13.42 12.44 13-0 392 393 i 12.53 13.24 11.55 12.26 12. 1 12.8 394 d 13.69 12.71 13.3 No. 2722 1893, Sept. 15 No. 2741 405 e 14.89 13.91 14.3 1893, Sept. 22 406 e 14.98 14.00 14.4 n h i3 m 407 c 14.98 14.00 14.4 410 a 14.34 13-36 13.7 411 a 14.79 13.81 14.2 412 e 15.28 14.30 14.7 414 e 14.70 13.72 I4.I 415 c I4.6O 13.62 14.0 417 d 14.44 13.46 13-8 418 d 15.08 14.10 14-5 420 f 14.60 13.62 14-0 422 c 14.79 13.81 14-2 429 e 14.51 13-53 13.9 428 e 15.38 14.40 14.8 No. 2756 1893, Sept. 23 n h 53 m No 2777 447 14.07 13.08 Mo 7 -LTV-f. ^/ / / 1893, Oct. 4 448 c 14.22 13-23 * w 13.8 ' 9" 1 6 m 450 c 14.42 13.43 14.0 45i c 14.78 13.79 14.4 452 c 14.42 13-43 14.0 455 a 15.05 14.76 14.06 14.7 !3>9 42.2 457 d 13.54 12.55 13.1 T^ * 22 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 5 6 No. 2777 Cont 'd. 4=;8 b I4.09 13.10 17.7 70.0 *fo w d 14.03 X O / 17.4 OV m y 7,0. 461 d 14.31 13.32 *J * t t 13.9 Oy *?r 462 j 14.47 17.44 17.7 41.1 ^ 463 J i - L *-r**-rO 14.22 X O T'T 1 13.23 x o / 13.8 464 n 13.81 12.82 13.4 465 I 13-81 12.82 13.4 466 n 12.76 11.77 12.3 467 f 14.13 13.7 468 d+f 13.81 12.82 13.4 469 d 13.54 12.55 13.1 471 I 14.09 13.10 13.6 472 a 14.31 13-32 13.9 473 h 14.67 13-68 14.3 474 f 14-13 I3.I4 13.7 No. 2787 470 a 14.00 27 A1 W ** J\J J 1893, Oct. 5 *T/ w 477 a *-*T ' V w 14.48 I3.49 */ *y 27 I0 h 22 m TV / *fcf *tfW */ ** No. 2791 481 h 14 ^6 i 26.1 39 .8 1893, Oct. 7 AjAJJi 482 h 14^4 j -j c e I0 h 26 m L^\J^ 483 f 13.97 12.98 25-7 39-7 65.5 484 f 13.87 12.88 25-3 39-0 65.3 48; f 13.84 12 8c. "7O ? 55-6 T"O 486 f 14.27 J.A .U J T7. 28 2^*2 ^06 ij.<_nj 487 d 1 o ^(J 25^8 *!**/ 488 d 14^2 J'eo 39.8 480 b 14^2 T7 C2 2^7 40.2 t'-'y h T4^7 I?^8 26.0 4O. I 4OI a 14.46 1^47 2C 7 40.7 4Q2 y 14. co J-3 60 ^3 *J *T V ' S O ty 40 c o. ^T" ' O.7 14.10 i O'^~ nJ 13.11 2C A 38.2 No. 2797 T".7O 493 g 14.68 13.69 14.4 O*" 7 " ** 1893, Oct. 9 494 g 14.68 13.69 14.4 8h I0 m 497 g 14.46 13.47 14.2 498 I 13.89 12.90 13.6 499 e 13.54 12-55 13.2 500 f 14.43 13-44 14.3 31.6 42.0 501 f 14.63 13.64 16.0 33-2 42.8 502 j 14.35 13.36 14.1 503 j 14-55 13.56 14.3 504 I 15.34 14-35 15.1 505 f 15.34 14.35 15.1 506 g 13.72 12.73 13.4 507 a 14.20 13.21 13.9 508 I 14.02 13.03 13.7 No. 2800 1893, Oct. 10 509 g S f 13.56 13.65 12.57 12.66 15.2 15.4 25.0 25-3 9028* 512 f 14.50 13.51 17.2 27.0 513 h 13.85 12.86 16.8 25-7 514 d 14.50 13-51 16.9 27.0 515 f 14.39 13.40 16.9 26.8 f 13.80 12. 8l 16.9 25.6 FROM THE MOTIONS OF THE CALCIUM FLOCCULI. TABLE i. Diurnal Motions of the Flocculi. Continued. 23 Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. i 2 3 4 6 No. 28ooCont'd. 517^ m I3.40 I2.4I 14.1 24.8 k 12-75 11.76 15.2 522 d 15.10 14.11 18.6 28.2 525 h 14.14 13.15 17.2 26.3 No. 2809 519 f 14.09 13.10 9-5 1893, Oct. ii 520 d 14.24 13.25 9.6 ^ho^rn 523 f 12.99 12.00 8.7 524 f 13.98 12.99 9.4 528 h 14.09 13.10 9.5 529 h 13.67 12.68 9.2 No. 2812 1893, Oct. 12 9h26 m No. 2818 530 d 14.87 13.88 14-3 27-5 1893, Oct. 16 531 d 14.60 13.61 14.2 27.0 io h 30 m 532 k 14.27 13-28 13.9 26.4 39-3 533 534 { 14.05 14.39 13.06 13.40 14.0 13-9 2$ f 14.70 13.71 14.2 536 j 14-39 13.40 13-9 537 I 14.30 13.31 14.3 26.4 538 I 14.10 13-11 13.6 539 k 14.10 13.11 13.6 26.4 38.8 541 i 13.71 12.72 13.2 24.9 37-6 543 j 14-39 13.40 13.7 26.6 544 I 13.98 12.99 13.4 25.8 545 I 14.79 13.80 14.6 27.4 546 I 13.29 12.30 12.6 24.4 548 e 15.27 14.28 14.8 549 i 14.35 13.36 14.1 26.8 39.6 550 k 13-73 12.74 13.2 552 c 15.01 14.02 14.9 27.8 553 a 14.99 14.00 14-5 554 a 15.48 14.49 15-0 556 h 14.34 13.35 14.8 27.0 40.0 No. 2821 540 i 13.91 12.92 12.5 24.8 1893, Oct. 17 542 k I3.8I 12.82 12.9 24.6 ii h 25 m 559 e 15.29 14.30 13.5 s6o 14 60 13.61 12 8 26.2 ^ ^ A. 5uu 56l h 13^86 12^87 I2.S 24.7 ' h 14.62 13.63 12.56 12.8 13.2 26.3 52.1 1 567 g g e 14.27 13-95 13-56 13.28 12.96 12.57 12.5 12.2 12.0 24.1 o** * 568 f 13.42 12.6 26.3 55.0 Ovn- 7 f f 14.01 1 3.02 ^^O 25.6 000 j ** No. 2829 569 m 13-43 12.44 12. 1 1893, Oct. 18 C7Q or 12.94 12.5 4i.3 io h 03 m OX" 571 & C 13.97 12.98 13.6 T" 1 - *O 572 C 14.34 13-35 13.0 24: THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 5 5 6 No. 2829 -Cont'd. 573 h 14.88 I3.89 13-5 C*7A f T A. OQ I3.IO 12.5 41.9 575 k 13.24 12.25 II.Q No. 2831 C77 c 14 24 13 25 20 3 1893, Oct. io O/f 14 24 13 25 29.3 * v '5ri.lJ x-rvrv x.y cgj e 14 24 T^" 2 e 20.3 582 i JC.7Q 14. 80 y o 32.7 No. 2839 o^** **?*/;/ &*f WVf O^** / 1893, Oct. 21 No. 2870 583 h 13.31 12.31 12.5 1893, Nov. 6 584 h 14.51 13.51 13.7 io h 5i m 585 / 15.70 14.70 14.9 C&fS / 14.01 13 OO 17. C 39-0 587 J f 14.08 A O ***** 13 07 * o * o 13.8 39i 588 7 j a 13.84 L O' < -'/ 12.84 *O h JarK 25 633 f 14.09 13.07 12.6 634 d 13.98 12.96 12.5 635 d 13.89 12.87 12.4 636 14.09 13.07 12.6 637 13.79 12.77 12.3 639 f 14.19 13.17 12.7 640 f 14.40 13.38 12.9 641 e 13-57 12.55 12. 1 642 g 14.09 13.07 12.6 644 d 13.69 12.67 12.2 648 j 14.51 13.49 13-0 650 f 13.79 12.77 12.3 651 I 13.79 12.77 12.3 652 653 I n 13-57 13.98 12.55 12.96 12. 1 12.5 No. 3028 1894, Jan. 26 II h 32 m No. 3062 654 f 14.70 13.70 13.7 1894, Feb. 27 h 14.30 13.30 13.3 i h 33 m 656 j 14.40 13.40 13.4 657 j 14.00 13.90 13.9 658 h 14.50 13.50 13.5 659 I 13.80 12.80 12.8 660 I 14.30 13.30 13.3 661 j I4.0O 13.00 13.0 662 j 14.30 13.30 13.3 663 j 13.90 12.90 12.9 664 J 14.30 13.30 13.3 665 j 13.90 12.90 12.9 666 j 13.90 12.90 12.9 667 j 14.40 13.40 13.4 668 h 14.80 13.80 13.8 669 f 14.80 13-80 13.8 670 c 14.70 13.70 13.7 671 a 13.80 12.80 12.8 672 b 14.80 13-80 13.8 673 b 13.80 12.80 12.8 674 a 14.70 13.70 13.7 675 e 13.70 12.70 12.7 676 i 15.10 14.10 14.1 677 d 15.00 14.00 14.0 678 f 14.80 13-80 13.8 No. 3069 679 h 14.71 I? 71 28.4 40.3 1894, Feb. 28 680 h A T"* / X x o / -* 68 1 h iTcU 12.93 26!? 38.4 682 f 14.22 13.22 AVS J 27.^ 38.8 683 j "'i ' O 27.0 38.8 684 h ic. 14 14 14 / * w 29.2 68=; x O * ^-T 1 14.35 13.35 27. C, v -"- 7 D 686 nt 13.00 12.88 * / J 687 k 27.7 \j\j / 1 26 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 5 6 No. 3079 1894, Mar. 2 3*1 10 m No. 3082 1894, Mar. 3 I2 h IO m No 3003 689 6 9 6 9 I 6 9 2 693 694 1 609 h f j j C e e i i k e I5.29 15.06 14.71 14.37 14.37 14.03 14.60 14.14 14.26 14.03 14 54 I4.29 I4.O6 I3.7I 13.37 13-37 13.03 13.60 13.14 13.26 13.03 1^, 54 12.5 12.3 12.0 ii. 7 ii. 7 11.4 11.9 "! ii. 6 11.4 28.4 1894 Mar 8 700 a 14 ^5 17 7,5 28.O Tih^em 7O2 f 14.64 17 64 28.6 70^ f 14.40 17 4O 28.1 7O4 f 14.40 I7.4Q 28.3 70 ^ f 14.40 I7.4Q 28.3 706 1 14.35 13.35 28.0 707 J f n.88 700 f 14.49 I7.4Q 2 o ., 710 y M.4Q I7.4Q 083 711 / I4.^O 17.70 27.0 712 / **I"O V ' 14 60 >-> I 7. 60 28.7 71^ y i^.uy I4.O4 1^.64 28.6 714 / 14.7.5 17.7,5 28.0 71 c \ I4.7Q 17.70 27.0 716 h 14.7!; 17.7,5 28.0 717 i 14.40 13.40 28.1 718 i 14.68 13.68 28.7 719 h 14.40 I 7. 4O VT 68.8 No. 3101 1894, Mar. 10 2^04 m No. 3104 1894, Mar. 13 2 h I2 m No. 3106 1894, Mar. 14 i h 59 m 721 722 723 724 725 726 727 728 729 730 733 736 74i 731 732 734 737 738 C C S e e c e S g b + d g f a b h e e 12.91 13.51 14.22 13.92 14.02 14.49 14.42 13.92 13.31 13.89 14.62 14.32 14.02 15.06 14.24 14.13 14.20 13.51 11.91 12.51 13.22 12.92 13.02 13.49 13.42 12.92 12.31 12.89 13.62 13.32 13.02 14.06 13.24 13.13 13.20 12.51 11.8 12.4 13.1 12.8 12.9 134 13.3 12.8 12.2 12.8 13.5 13-2 12.9 13.6 13-6 12.7 12.7 12. 1 25.6 26.4 25-7 26.9 26.2 39-6 38.8 38.7 5i.i FROM THE MOTIONS OF THE CALCIUM FLOCCULI. TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. i 2 3 4 5 6 No. 3io6Cont'd. 739 e 14.23 I3.23 12.8 740 c 14.50 13.50 13.2 27.4 743 a 14.95 13-95 13.5 748 d 14.98 13.98 13.1 28.0 40.8 No. 3112 744 d 14.87 13.88 14.7 27.1 1894, Mar. 15 I h I2 m 746 d d 14.20 15-12 13-21 14.13 13.8 15.4 25-8 2 7 .6 747 f 15.17 I4.I8 15.4 27.7 749 b 14.71 13.72 14.6 No. 3117 750 d 15.39 14.40 12.8 1894, Mar. 16 751 b 14.60 I3.6l 12. 1 2h 44 m 752 h I3.8I 12.82 11.4 753 h 14.38 13-39 11.9 754 { 15.39 14.60 14.40 I3.6l 12.8 12. 1 756 i 14.72 13-73 12.2 757 i 14.60 I3.6l 12. 1 758 c 13.25 12.26 10.9 759 g 14.60 I3.6l 12. 1 760 c 14.15 I3.l6 ii. 7 No. 3121 1894, Mar. 17 I2 h 04 m No. 3185 76! a 14.30 13-34 13.7 1894, May 30 762 c 14.98 I4.O2 14.4 3hi6 m 763 i 14.59 13.63 14.0 764 e 14.98 14.02 14.4 765 e 14.20 13.24 13.6 766 g 14.78 13.82 14.2 767 e 14.20 13.24 13.6 768 c 14.30 13.34 13.7 769 f 14.49 13.53 13.9 770 I 13.60 12.64 14.2 24.2 771 f 14.69 13.73 14.1 773 d 14.49 13-53 13-9 774 f 14.48 13.52 14.7 25.9 775 f 13.96 13.00 14.2 24.9 776 c 14.10 13.14 13.5 777 i 13.38 12.42 14.0 23-8 778 g 1440 13.44 13-8 779 c 14.59 13.63 14.0 780 e 14.49 13-53 13.9 No. 3190 1894, May 31 3 h 55 m No. 3191 781 g 14.41 1^.4=5 24.8 rt 1894, June 2 / w A 782 T^'T I4.2O A O *T- D T^ 24 ^ /u^. 783 I^\4 *""T- O 24.6 /*-*O 784 MC7 IT. C7 40.6 53-8 785 a oo 14. -34 * O O / i 23.7 T^ * 39>2 53.1 786 g H^'OH 14.52 iV^6 2=5.0 787 P 14. ? o ' 1 /: 24 6 /*"*/ & ' 28 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 5 6 ^[o. 3101 Cofit'd, 788 CF 14 41 13 4^ 24 8 /uu & Aif.ifi A 04O A^U 780 0- 1^6^ 12.69 27 4 / *("*"-' 14 70 "O- J - w n.8^ 26: 40. Z J. i^\J * o IIC2 g LL T* / y 14 40 X O >W O 17.44 2^ ^ T'^'O 52.8 * A O^ HC7 g L T > i T^ / 14 08 * O T'T' 1^.12 ^O'O 2^ 7 ^84 J*** v ' No. 3374 * * oo 1154 c l.f WJ 14.86 * o *** 13.90 14.0 ^o*/ 28.2 1894, Aug. i 1155 g 12.94 11.98 12.2 ii h 37 m 1161 e 14.64 13.68 I4.I 27.7 1162 e 13-93 12.97 13.2 1163 a 15.11 14.15 14.4 1164 1165 a a 15-11 14.52 14-15 13-56 14.4 14.2 27.4 1166 a 14.71 13.75 14.0 1167 d 14.52 13-56 13-8 1168 f 13.83 12.87 I3.I 1170 a 14.22 13.26 13.5 1171 a 14.61 13.65 13.9 1172 c 14.76 13-80 14.2 27.9 No. 3382 H73 e 14.46 13-50 13-6 28.5 1894, Aug. 2 1174 i 13.72 12.76 12.8 I2 h 03 m H75 i 14.01 13-05 I3.I 1176 e 15.01 14.05 I4.I 1177 e 14.61 13.65 13.7 1178 c 14.51 13.55 13-6 1179 g 14.71 13.75 13-8 1180 a 14.81 13.85 13.9 1181 c 14.81 13.85 13.8 29.2 1182 c 14.41 13-45 13-5 1183 a 14.11 13-15 13.7 27.7 1184 e 14.19 13-23 12.7 27.9 1185 a 15.00 14.04 13.7 29.6 1186 g 14.21 13-25 13.3 1188 g 14.11 13-15 13.2 1189 c 14.11 13-15 13.2 FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 35 TABLE I. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. i 2 3 4 5 6 No. 3388 II9I f 15-01 14.05 15-5 1894, Aug. 3 1192 a 16.01 15.05 16.6 I2 h o8 m H93 a 16.36 15.40 17.0 No. 3394 1 104 h 14.62 13.66 28.4 40.6 1804 Aufir 4 A Ay -4- 14.67 13.71 28.2 40.8 i Ljy^| j ^&.ug^ ^-f 1106 ft **?*"'/ 14.47 27.3 No. 3398 1197 d **f *f/ 14.60 13.64 13.0 1894, Aug. 6 1198 d 14.50 13.54 12.9 3h 07 m 1199 1 200 c c 14.71 15-44 13.75 14.48 13^8 1 201 c 14.89 13.93 13.5 27.5 1202 c 14.50 13.54 12.9 1203 c 14.82 13-86 13.6 27.5 39-4 I2O4 c 15.12 I4.l6 13-8 28.4 40.2 1205 c 15.44 14.48 13-8 1207 e 15-44 14.48 13-8 1209 1210 c c 14.25 14.76 13.29 13.80 12.5 12.7 26.2 27.4 37-7 39-2 I2II e 14.37 13.41 13.5 27.2 38.2 1212 g 13.48 12.52 12.2 24.8 1213 1214 c e 14.39 14.64 13.43 13.68 12.7 13-0 26.5 27.0 1216 a 15.13 14.17 13.5 1217 a 15.13 14.17 13.5 1218 a 15.02 14.06 13-4 1219 S 13.84 12.88 12.8 25.2 36.6 1222 c 13.73 12.77 13.0 25.2 1223 c 14.92 13.96 13-3 No. 3405 I2O6 g 14.64 13-68 13-3 25-8 1894, Aug. 7 1215 c 14.73 13.77 13.7 26.0 i h 59 m 1220 c 14.98 14.02 14.3 1221 e 14.20 13.24 13-5 1224 c 14.79 13.83 I4.O 26.1 1225 g+i 13.71 12.75 13.0 1226 e 14.69 13.73 14.0 1227 c 15.28 14.32 14.3 27.0 1229 a 15.36 14.40 15.2 27.2 No. 3411 1230 e 15.39 14.43 12.5 1894, Aug. 8 1231 c 14.93 13.97 12. 1 2 n 28 m 1232 e 15.05 14.09 12.2 1233 e 14.01 13-05 ii. 3 1234 d 15.16 14.20 12.3 1236 d 14-93 13.97 12. 1 1237 c 14.93 13-97 12. 1 No. 3417 1894, Aug. 9 No. 3424 1239 f 14.16 13.20 28.1 1894, Aug. 14 1240 f 13.83 12.87 27.4 io h 56 m 1241 d 14.25 13.29 28.3 36 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. i 2 3 4 5 6 No. 3424 Confd. 1242 C 14.96 14.00 29.8 1243 a 14.49 13.53 29.2 42.0 1249 e 14.28 13.32 28 4 41.4 12^1 d 14.02 I -3 06 27 8 *T* " J--&3 i 12^2 o j. ^ . w\^ 12 77 ^ / .u 27 2 No. 3429 A - fi 'O 1253 & e 14.12 ' / / I3.I6 13.3 *"i ** 24.4 1894, Aug. 16 1254 e 14.05 13.09 13-4 24.3 2h 2m 1255 1256 c c 14.11 13.89 13.15 12.93 12.9 12.7 24.0 1257 e 14.64 13.68 13.5 25-4 1258 g 14.42 13.46 13.2 1259 i 14.31 13-35 13-1 I26O i 14.72 13.76 13.5 I26l h I4.8l 13.85 13-5 25.7 1263 m 13.60 12.64 12.4 1264 f 14.01 13.05 12.8 1265 1266 f f 13.99 15.03 13.03 14.07 12.0 13.8 24.2 1267 f 13.70 12.74 12.5 No. 3439 1268 e 15.02 14.06 12.3 1894, Aug. 17 1269 e 14.45 13-49 1 1. 8 I h 35 m 1270 d 15.02 14.06 12.3 1271 h 14.67 I3.7I 12.0 1272 d 15.25 14.29 12.5 1273 h 15.13 14.17 12.4 1274 c 14.79 13.83 12. 1 1275 c 14,67 13.71 I2.O 1276 1277 a a 15-47 14.67 I4.5I 13.71 12.7 12.0 1278 1280 a b 15.70 15.02 14.74 14.06 12.9 12.3 1282 e 13.76 12.80 II. 2 1283 i 14.56 13.60 11.9 1284 11.70 10.74 9.4 1285 m 12.73 11.77 10.3 1286 k 13-53 12.57 II. 1287 q 13-53 12.57 II. No. 3441 1894, Aug. 18 io h 35 m No. 3447 1288 h 14.48 13.52 13.6 1894, Aug. 21 1289 d 14.36 13.40 13.5 26.9 I0 h 52 m 1290 b 14.18 13.22 13.3 1291 c 14.88 13.92 14.0 1292 e 14.48 13.52 13.6 1293 c 13.98 13.02 13.1 f 14.48 13-52 13.6 1296 j 14.78 13.82 13.9 1297 j 14.68 13.72 13.8 1298 d 14.38 13.42 13.5 1299 e 13-93 12.97 13.8 26.0 1300 f. 13.98 13.02 13.1 1305 i 13.29 12.33 12.4 FROM THE MOTIONS OF THE CALCIUM FLOCCULI. TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 f 6 No. 3453 1307 i I3.27 12.31 12.3 1894, Aug. 22 IlhOO m 1308 1309 b g 14-77 14.28 I3.8I 13.32 13.8 13.6 28.2 1310 i 14-37 13.41 13-7 28.4 1311 i 14.27 13.31 13-3 1312 g 14.27 13.31 13-3 1313 s 14-57 I3.6I 13.6 1314 i 14.17 13.21 13.2 1316 g 14.37 13.41 13.4 1317 g 14-57 I3.6l 13.6 1318 e+g 14.75 13-79 14.0 29.2 1319 g 14.14 I3.I8 13.4 27.9 No. 3456 1320 i 13.88 12.91 14.9 26.2 1894, Aug. 23 1321 d 14.30 13-34 14.9 io h 59 m 1322 k 13-94 12.98 14.5 1323 m 13.85 12.89 14.4 1324 h 14.12 13.15 14.3 26.6 1325 K 13-68 12.72 14.2 No. 3462 1326 d 14.22 13.25 12.0 1894, Aug. 24 1327 f 14.22 13.25 12.0 i h 47 m 1328 i 13.34 12.37 II. 2 1329 m 13.89 12.92 ii. 7 1330 i 13.01 12.04 10.9 1332 k 13.78 12.81 n.6 1333 b 14.33 13.36 12. 1 1334 b I4.OO 13.03 11.8 No. 3464 1894, Aug. 25 n h 3i m No. 3467 1335 a 14.24 13.27 13.2 1894, Aug. 31 1337 b 14.14 13.17 13.1 2 h I 8m 1338 g 13-94 12.97 12.9 1339 k 12-53 11.56 H.5 1340 g 14.04 13.07 13-0 1341 c 14-95 13.98 13-9 1342 c 14.24 13.27 13-2 1344 e 14.24 13.27 13-2 1345 a 14.14 13.17 13-1 1346 i 14-34 13.37 13-3 1347 a 14.85 13.88 13-8 1348 g 13.94 12.97 12.9 1349 f 14.24 13.27 13.2 1350 h 13-74 12.77 12.7 No. 3473 1894, Sept. i 2 h I0 m No ^476 I-JCC d 17. 60 12.72 38.1 A! v ^L^f\J 1804. Scot. * ^OOu I7C6 m J.J.V.7V, 13.67 12.70 26.1 37-9 j.uvyf.} w^\^^u. j 2 n 26 m *O J w 1^7 tn I -3 QQ 1^ 02 26.6 *J/ ^7 ^8.0 i OJ/ *-o'yy A O *-''' o^ j * y 38 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE i. Diurnal Motions of the Flocculi. Continued. Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 5 6 No. 3479 1894, ^Sept. 7 No. 3488 1894, Sept. 17 1377 1378 d d 14.91 14.91 13.93 13.93 15-0 I5.I 27.6 27.6 2h 3 2 m 1379 d 14.91 13-93 14.8 1380 d 15.85 15-8 1381 f 14.46 13.48 14.5 26.7 1382 d 15.31 14-33 15.6 28.4 1383 b 15.19 14.21 I5-I 1384 e 15.10 14.12 15.0 1385 i 14.05 13.07 14.4 25-9 1386 i 14.15 13.17 14-3 26.1 1387 i 13.70 12.72 14.0 25.2 1388 I I3.58 26 9 i O'-"-' 1389 i 14.40 13.42 14.3 26.6 1300 a 13 ^7 M.-3 27 67 6 "Ob/*-' 1391 b 14.75 o *o/ 13.77 O 14.4 */ ** 27.3 \j / \j 1392 b 14.34 13.36 14.2 1393 a 15.10 14.12 15.0 1394 a 14.72 13.74 14.6 1395 d 14.65 13.67 15.0 27.1 1396 f 14.65 13.67 14.6 27.1 1397 f 14.06 13.08 13-9 1398 f 15.10 14.12 15-0 1399 I 14.15 13.17 I5-I 26.1 1400 j 13.69 12.71 13-5 1401 14-35 13-37 14.6 26.5 1402 i 15-00 14.02 14.9 1403 b 14.72 13-74 14.6 1404 d 14.76 I3.78 14.7 27.3 1405 a 14.82 13.84 14.7 1406 n 13-35 12.37 13.0 24.5 1407 b 14.56 13.58 14.5 26.9 1408 b 14.58 13.60 14.9 27.2 67.7 No. 3493 1409 k 14.27 13.29 12.2 **/ " w / ' / 1894, Sept. 18 1410 k 13.51 12-53 H-5 4 h 03 m 1412 f 14.38 13.40 12.3 1413 h 13.83 12.85 ii. 8 1414 I 13.83 12.85 1 1. 8 No. 3498 1894, Sept. 19 2 h 05 m No. 3503 1417 t[ 13.70 12.72 23.0 37.6 1894, Sept. 22 1418 o p 13.06 24.8 39.2 ' -L4"T X1-/ 1419 & s n'.SS 10.90 .....1 20.5 O;J ** No. 3507 1894, Sept. 24 I42O 1421 g e 13.75 13.40 12.77 12.42 14.3 13.9 I0 h 53 m 1422 a 14.20 13.22 14.9 28.2 1423 a 14.34 13.36 14.9 28.5 1424 a 14.77 13.79 15-3 29.4 FROM THE MOTIONS OF THE CALCIUM FLOCCULI. TABLE i. Diurnal Motions of the Flocculi. Continued. 39 Plate No. and date. No. Zone Diurnal motion, sidereal. Diurnal motion, synodic. I 2 3 4 5 6 No. 3507 Confd. 1425 a I4.38 I3.40 14.7 28.6 1426 g 14.44 13.46 14.8 28.7 1427 d 14-74 13.76 15.4 No. 3509 1428 e 14.48 I3.50 13.7 1894, Sept. 25 1429 e I4.I8 13.20 13-4 i h 45 m 1430 g 13.79 I2.8I 13-0 1431 e 14.58 I3.60 13-8 1432 d 13.69 12.71 12.9 1433 h 14.18 13-20 13.4 1434 h 14.58 13.60 13.8 1436 c 14.58 13.60 13.8 No. 3516 1894, Sept. 26 2 h o6 m No. 3528 1438 e 14.33 13-35 ii. i 1894, Sept. 28 1439 e 14-57 13-59 II .3 2 h 34 m 1440 c 14-93 13-95 11.6 1441 c 14.45 13.47 II. 2 1442 h 1445 13.47 II. 2 1443 h 14.09 13.11 10.9 1444 f 14.33 13.35 II. I 1445 h 13.85 12.87 10.7 1447 h 14.69 13.71 11.4 1448 b 15.05 14.07 11.7 1449 a 13-97 12.99 10.8 1450 a 14.45 13-47 II. 2 1451 e 14.21 13.23 II. 1452 c 14.21 13.23 II. O 1453 a I4.8I 13.83 II-5 1454 c I5.I8 14.20 11.8 No. 3533 1894, Sept. 29 io h 3i m The diurnal motions (|) of all the flocculi lying within each zone five degrees wide are grouped in table 2. The mean diurnal motion for each zone, together with its probable error, and the equivalent rotation period in days, are also given. In deriving the mean, the diurnal motions are weighted according to the interval in days. 40 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE 2. Diurnal Motions Corresponding to each Five-Degree Zone. [Zone a = o to 5. Mean Diurnal Motion == 14.72 0.031.] Diurnal Diurnal Diurnal Diurnal No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. 9 8 I I4.67 819' I 14.64 1030 I 15-03 H93 I 16.36 106 5 14.62 820 I 14.92 1034 2 14-95 1216 I 15.13 104 3 13.56 821 2 14.35 1035 2 15.28 1217 I 15.13 91 i 14.06 827 2 14-59 1036 2 14.82 1218 I 15-02 107 302 2 2 13.80 14.57 842 853 4 3 15.00 14.75 1045 1046 2 14-95 14.65 1229 1243 2 3 15.36 14.49 410 I 14-34 877 3 14-49 1047 14.74 1276 i 15-47 411 I 14.79 898 2 14-59 1060 14.26 1277 I 14.67 455 I 15.05 899 2 14.21 1061 14.98 1278 i 15.70 472 I I4.3I 936 2 14.91 1062 15.09 1335 I 14.24 470 2 14.90 936' I 14.54 1068 3 14-55 1345 i 14.14 477 2 14.48 953 I 14.41 1076 3 14-43 1347 I 14.85 491 3 14.46 970 I 14.15 1136 2 15.26 1390 5 14-55 507 14.20 972 I 13.82 1163 I5-II 1393 i 15.10 553 14.99 977 2 14.39 1164 15-11 1394 i 14.72 554 15.48 978 I 15.20 1165 14.52 1405 i 14.82 | 588 13.84 985 2 15.09 1166 14.71 1422 2 14.20 608 2 14.70 987 I 15.07 1170 14.22 1423 2 14-34 671 13.80 988 I 14.55 1171 I4.6l 1424 2 14.77 674 14.70 1013 4 14.26 1180 I4.8I 1425 2 14.38 731 I 15.06 1014 5 14.44 1183 2 14.11 1449 I 13.97 743 I 14.95 1015 2 14.14 1185 2 15.00 1450 I 14-45 761 I 14.30 1016 3 14.57 1192 I 16.01 1453 I I4.8I 785 4 14.34 [Zone b = o to 5. Mean Diurnal Motion = 14.57 0.045.] 32 i 13.99 458 3 I4.09 882 I 14.78 1063 i I5.25i 34' 2 14.72 489 3 14.52 897 2 14.92 1093 2 13.56 38 I 15.24 672 i 14.80 918 2 14.19 1280 I 15.02 36' 2 I3.8I 673 i 13.80 924 I 15-38 1308 I 14.77 36" 38'" 2 I 14.26 14.57 719 733 5 i 14.40 14.62 925 934 I 4 14.99 14.56 1290 1333 I I 14.18 14-33 52 5 14.75 732 2 14.24 945 2 14-95 1334 I 14.00 53' i 14-73 749 I 14.71 954 I 14.54 1337 I 14.14 55 5 14.68 75i I 14.60 955 I 14.14 1383 I 15.19 87 2 14.66 793 2 15.13 971 2 14.19 I39i 2 14-75 217 15.12 828 I 14.73 973 2 14.86 1392 I 14-34 225 i 13.88 850 2 15.34 974 I 15-71 1403 I 14.72 230 12.37 879 I 15.20 975 3 14.65 1407 2 14.56 264 I5.I8 880 I 14.64 976 2 14.75 1408 5 14.58 315 i 15.84 881 I 14.50 1059 I 15.39 1448 i 15.05 361 14.30 [Zone c = 5 to 10. Mean Diurnal Motion = 14.50 0.027.] i 3 I4.74 183 I3.55ii 447 3 14.07 572 i 14-34 19 3 14.84 184 15-45 448 i 14.22 577 2 14.24 i' 3 14.62 38i 15.84 450 i 14.42 578 2 14.24 37' 3 14.37 382 14.30 451 i 14.78 670 I 14.70 78 2 14.33 386 13.69 452 i 14.42 693 I 14-37 82 I 15.13 407 14.98 456 3 14.76 702 2 14.64 106' I 14.40 415 14.60 552 2 15.01 703 2 14.40 132 5 13.70 422 14-79 57i I 13-97 704 2 14.49 FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 41 TABLE 2. Diurnal Motions Corresponding to each Five-Degree Zone. Continued. [Zone c = 5 to 10. Mean Diurnal Motion = 14.50 0.027. Continued.] Diurnal Diurnal Diurnal Diurnal No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. 721 I I2.9I 904 3 14.44 1057 14-57 1222 2 I3.73 722 I 13.51 912 3 14.47 1085 14.55 1223 I 14.92 726 2 14.49 921 2 14-57 1104 < 14.11 1215 2 14.73 740 2 14.50 922 2 14.29 1131 14.97 1220 I 14.98 758 I 13.25 92O 2 13.90 1132 14-57 1224 2 14.79 760 I 14.15 928 3 14.25 H33 13.87 1227 2 15.28 7 62 I 14.98 947 I 14.27 H54 2 14.86 1231 I 14.93 768 I 14.30 948 I 13.46 1172 2 14.76 1237 I 14.93 776 I 14.10 949 I 14.95 1178 I 14.51 1242 2 14.96 779 I 14.59 963 I 12.79 1181 2 I4.8l 1255 I 14.11 784 4 14.53 982 2 14.70 1182 I 14.41 1256 2 13.89 822 i 14.64 984 2 14.34 1189 I 14.11 1274 14.79 823 i 14.82 996 2 14.38 1199 I 14.71 1275 14.67 825 i 14.36 1017 2 14.30 1 200 I 15.44 1291 14.88 826 i 14.45 1018 2 14.57 1201 2 14.89 1293 13.98 822' i 14-73 1031 I 14.72 1202 I 14.50 1341 14-95 843 4 14.70 1032 I 15.24 1203 3 14.82 1342 14.24 861 i 14.52 1033 3 14.42 1204 3 15.12 1436 14.58 862 i 15.14 1037 i 15.03 1205 i 15.44 1440 I 14-93 872 i 13.99 1038 i 14.83 1209 3 14.25 1441 I 14-45 873 3 14.17 1044 2 14.90 I2IO 3 14.76 1452 I 14.21 891 2 14.28 1046 I 14.65 1213 2 14.39 1454 I I5.I8 903 2 14.76 1050 I 14.06 [Zone d = 5 to 10. Mean Diurnal Motion = 14.55 0.030.] 27 3 I4.42 364 I I4.39 750 I 15-39 1093 2 13.56 36 2 14.62 365 I 13.69 773 I 14.49 1116 2 14.82 35 3 15.87 387 I 13.52 792 2 14.57 1129 2 14.67 5i 5 14.69 394 I 13.69 795 2 14.27 1130 14.50 Si' 3 14-93 417 I 14.44 805 I 14.21 1141 15.07 57' I 14.78 418 I 15.08 829 I 15-11 1167 14.52 50 2 15.08 457 I 13-54 841 3 14.82 1197 14.60 75 2 14.03 459 3 14.03 866 i 15.05 1198 14.50 109 2 I4.52 461 i I4.3I 876 3 14.15 1234 I5.l6 138 6 14.58 468 i I3.8I 878 i 13.80 1236 14-93 168 4 14.64 469 i 13-54 883 i 15.20 1241 14.25 168' 4 14.75 487 2 14.52 894 2 14-43 1251 14.02 165' 3 I4.52 488 3 14.52 896 2 14.54 1270 15.02 165 i 14.06 5M 2 14.50 943 2 15.00 1272 15.25 228 i 14.46 522 2 15.10 964 I 15.48 1289 14.36 232 3 14.72 520 I 14.24 969 I 14.23 1298 14.38 242 3 14.48 530 2 14.87 990 2 14.64 1321 14.30 258 i 14.87 531 2 14.60 1026 3 15.00 1326 14-22 259 i 14.42 j 615 I 14.56 1052 i 14.98 1355 3 13.69 261 i 15.03 631 I 14.06 1058 i 14-37 1377 2 14.91 304 3 13.62 I 634 I 13.98 1065 I I4.l6 1378 2 14.91 314 i 14.41 635 I 13.89 1069 2 15.20 1379 I 14.91 316 i 14.12 644 I 13.69 1073 I 14.96 1380 I 15.85 347 3 14.06 677 I 15.00 1074 2 15.20 1382 2 15.31 356 | 3 15.19 ! 733 I 14.62 1075 4 14.41 1395 2 14.65 357 4 I4-I3 748 3 14.98 1071 i 13.71 1404 2 14.76 358 4 I4.l6 744 2 14.87 i 1077 i 14.76 1427 i 14.74 362 i 14.30 745 2 14.20 ! 1092 2 14.09 1432 i 13.69 363 i 14.20 746 2 15-12 42 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE 2. Diurnal Motions Corresponding to each Five-Degree Zone. Continued. [Zone ^ = 10 to 15. Mean Diurnal Motion = 14.34 0.024.] Diurnal Diurnal Diurnal Diurnal No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, s dereal. 5' 3 14.42 559 I 15.29 902 14.25 1176 I 15.01 2 14.02 567 2 13.56 915 13-99 1177 I I4.6l A f I 14.38 58i 2 14.24 916 14-75 1184 2 14.19 2' 4 14.42 641 I 13-57 919 14-75 1207 I 15-44 33 2 14.78 675 I 13.70 895 14.58 I2II 3 14.37 23' I 14.15 694 I 14.03 929 13.70 1214 2 14.64 42 I 14.73 695 I 14.60 935 4 14.40 1221 I 14.20 42' 2 14.19 699 2 14-54 937 2 I4.3I 1226 I 14.69 44 3 13.69 724 I 13.92 950 I 13.87 1230 I 15-39 44' 2 14.41 725 4 14.02 1005 2 13.97 1232 I 15.05 56' I 13.93 737 3 14.20 1019 2 14.62 1233 I I4.OI 71 I 14.58 738 i 13.51 1020 2 14.30 1249 3 14.28 78' 2 14.71 739 i 14.23 1049 3 14.69 1253 2 14.12 84 129 3 3 15.27 14.10 727 764 i i 14.42 14.98 1051 1082 I 3 13.55 14.08 1254 2 2 14.05 14.64 185 i 13.99 765 i 14.20 1083 3 14.77 1268 15.02 223 2 14.63 767 i 14.20 1084 3 14.21 1269 14-45 233 I 14.82 780 i 1449 1094 4 13-99 1282 13.76 252 2 I4.6l 781 2 14.41 HIS 2 I4.3I 1292 14.48 253 4 14.15 782 2 14.20 1118 2 14.08 1299 13-93 268 3 14.79 783 2 14.30 1125 2 13.78 I3l8 14-75 289 4 14.12 786 2 14.52 H35 I 13.19 1344 14.24 344 3 14.06 790 2 13.87 H45 I 13.87 1384 15.10 405 406 i i 14.89 14.98 1 798 807 I I 14.21 14.51 1149 1151 2 3 14.01 14.79 1421 1428 13.40 14.48 412 i 15.28 1 824 I 14-45 1152 4 14.40 1429 I4.I8 414 i 14.70 869 I 14.26 H53 3 14.08 1431 14.58 429 i 14.51 871 I I4.6l 1161 2 14.64 1438 14.33 428 i 15.38 i 874 5 14.30 1162 I 13-93 1439 14.57 499 i 13.54 i 901 i 14.25 H73 2 14.46 1451 14.21 548 i 15.27 i [Zone f = io to 15. Mean Diurnal Motion = 14.39 0.020 ] 18 2 I4.26 248 6 14.96 373 I5.I7 535 I I4.70 26' I 14.41 249 i 12.98 374 14.67 56o 4 14.60 54 4 14.57 251 4 14.33 420 14.60 568 4 14.41 60 3 14.01 260 i 15.32 467 I4.I3 555 4 14.01 61 4 14.14 263 i 15.32 468 I3.8I 574 3 14.09 64' i 13.97 265 i 14.06 474 14.13 585 I 15.70 79 2 13.74 297 3 14.69 483 5 13-97 586 3 14.01 92 2 14.67 298 3 14-88 484 5 13.87 587 3 14.08 99 I 14.67 304 3 13.62 485 5 13.84 589 i 15.39 93' I 13.65 305 3 14.42 486 3 14.27 592 3 14.45 103 116 3 2 13-97 14.11 326 i i 13.84 13.74 500 3 3 14.43 14.63 596 632 i i 14.80 14.19 124 5 14.14 330 i 15.26 505 i 15.34 633 14.09 133 4 14.31 353 4 14.26 512 2 14.50 636 14.09 141 3 14.40 354 3 I4.6l 515 2 14.39 639 14.19 142 i 14.63 355 3 14.52 2 13.80 640 14.40 163 5 14.55 360 3 14.44 519 I 14.09 650 13-79 145 i 12.78 367 i 14.39 523 I 12.99 654 14.70 164' 3 15.01 368 i 13.15 524 I 13.98 669 14.80 191 i 14.36 372 i 14.77 533 2 14.05 678 14.80 i FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 43 TABLE 2. Diurnal Motions Corresponding to each Five-Degree Zone. Continued. [Zone f = 10 to 15. Mean Diurnal Motion = 14.39 0.020. Continued.] Diurnal Diurnal Diurnal Diurnal No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. 682 3 14.22 832 2 14.87 967 I 14.56 1079 I 13-97 6 9 i 15.06 833 5 14.36 968 2 14-39 IH3 6 14.63 705 2 14.49 839 2 14-43 98! I 13-99 1142 I 15.37 709 2 14.49 840 2 14.65 986 3 14.65 H43 I 14.86 710 2 14.49 840' I 15.01 991 4 14-35 1168 I 13.83 711 2 14.30 844 2 14.86 992 2 14.38 1191 I 15.01 712 2 14.69 845 I 14.32 993 2 14-34 H95 3 14.67 713 2 14.64 846 I 14-73 994 2 14.20 1239 2 14.16 714 2 14-35 848 I 14.42 995 2 14.14 1240 2 13.83 741 I 14.02 851 3 14.48 IOOI I 14.89 1264 I 14.01 747 2 15.17 852 3 14-51 1003 I 13.96 1265 2 13.99 15-39 860 14.87 IOIO 2 14.69 1266 15.03 769 14.49 868 14.87 1028 I 14.21 1267 13.70 771 14.69 875 13.87 1029 I 14.21 1294 14.48 774 14.48 884 14.92 1039 I 14.62 1300 13.98 775 13.96 885 14.08 1040 I 14.41 1327 14.22 813 14.92 886 15.06 1053 I 14-57 1349 14.24 8i5 I3.6l 892 13.80 1054 I 14-37 1381 14.46 816 817 14.54 14.36 893 917 2 I 14-43 14.88 1064 1066 2 I 15.22 14.52 1396 1397 14.65 14.06 818 15.01 944 2 15.10 1067 3 14.90 1398 15-10 819 2 14-45 946 I 14.14 1070 i 13-50 1412 14.38 830 2 14-35 966 2 14-75 1072 I 14.47 1444 14-33 [Zone g= 15 to 20. Mean Diurnal Motion = 14.18 0.028.] 23 46 4 4 14.06 14.15 320 338 I I 15.21 14-34 797 808 i i 14-31 13.60 1140 1146 I 14-57 14.07 58' I 15-47 339 4 14.28 809 i 13.19 1147 14.07 70 I 14.58 380 i 13-15 810 i 14.11 H55 12.94 77 I 14.58 492 2 14-59 863 3 14.56 11 79 14.71 68 3 14.26 493 I 14.68 900 i 14.01 1186 14.21 83 5 13.97 494 I 14.68 905 I 14-75 1188 14.11 77' 2 14-37 497 I 14.46 906 I 15.26 1212 2 13.48 89 2 I3-8I 506 I 13.72 913 i 13-74 1219 3 13.84 90 4 13-88 509 2 13.56 938 3 14.46 1206 2 14.64 101 3 13-81 2 13-65 939 3 14-50 1225 I 13-71 108' 108 5 2 13.55 13.42 1 I I 14.27 13-95 940 951 4 i 14.08 14-95 1252 1258 2 I 13.73 14.42 118' 4 13-57 570 3 13-93 952 i 14-95 1309 2 14.28 in 2 14.40 613 i 13.96 979 i 13.32 1312 14.27 112 2 13-89 614 i 14.27 1042 2 14.85 1313 14-57 108" 2 15-27 642 i 14.09 1043 2 14.25 I3l6 14-37 143 I 14.21 700 2 14-35 1055 I 14.26 1317 14-57 134 I 14.29 723 14.22 1056 I 13.96 1318 14-75 208 I 14.40 728 13.92 1081 3 14.27 1319 14.14 236 2 14.72 729 13-31 HOI 2 14.60 1325 13.68 240 2 14.87 730 13.89 1 102 4 14.42 1338 13-94 241 2 14-77 736 14-32 H03 2 14.04 1340 14.04 254 2 13-73 759 14.60 1107 4 14.33 1348 13-94 244' 2 13-68 766 14.78 1108 2 13.62 1401 2 14-35 273 4 14.01 778 14.40 1123 4 13.76 1417 4 13-70 281 5 13.72 787 2 14.30 1126 2 13.68 I4l8 3 14-04 301 4 14.38 788 2 14.41 1134 I 14.07 1420 i 13-75 306 3 14-13 789 2 13-65 1138 I 14.38 1426 : 2 14.44 319 i 14.67 794 I 13-93 1 139 I 14-57 1430 I 13-79 44 THE ROTATION PERIOD OF THE SUN AS DETERMINED TABLE 2. Diurnal Motions Corresponding to each Five-Degree Zone. Continued. [Zone h 15 to 20. Mean Diurnal Motion = 14.32 0.031.] Diurnal Diurnal Diurnal Diurnal No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal . 14 I I3.78 2 5 6 4 13.84 563 4 13.55 849 3 I4.57 15 2 13.89 257 I 14.94 573 I 14.88 855 3 14.27 26 I 12.54 262 I 15.79 583 I 13.31 864 I 15.23 47' 4 14.22 266 I 15.71 584 I 14.51 86 7 I 15.14 49 3 14.64 271 I 13-86 590 I 14-33 870 4 14.37 47" 2 13.29 2 7 6 5 14.08 594 I 13-93 890 4 14.40 62 4 14.66 280 5 14.08 607 2 14.50 88 7 2 14.65 62' I 13.65 283 3 14.42 603 I I4.6l 965 I 13.73 79' 2 14.11 284 3 13.63 611 I I4.IO 1002 I 14.52 80 2 14.17 290 2 14.58 637 I 13-79 1004 I 14.80 49' 2 14.74 291 2 14-57 655 I 14.30 ion 2 14.74 80" I 13.56 292 2 14.58 658 I 14.50 1025 I 14.41 H3 2 13.89 310 I I4.O2 668 I 14.80 1027 I 14.52 114 2 14.10 329 4 14.09 679 3 14.71 1041 I 14.52 136 2 14-37 331 4 14.04 680 2 14.52 1048 2 14.48 150 2 13.84 333 i 14.92 681 3 13.93 1078 I 13-44 150' 2 14-54 345 3 13-66 683 3 14.13 1194 3 14.62 156 2 15.84 346 3 14.06 684 2 15.14 1196 2 14.47 155 2 14.25 391 i 13.42 689 I 15.29 1261 2 I4.8I 150" 13.23 393 i 13.24 715 2 14.30 1271 14.67 174 15.11 473 i 14.67 716 2 14-35 1273 15.13 175 13-86 481 3 14.56 718 2 14.68 1288 14.48 176 14.15 482 3 14.54 734 14.13 1324 14.12 211 14.40 490 3 14.57 752 I3.8I 1350 13.74 212 14.50 513 2 13.85 753 14.38 1413 13.83 210 2 14.21 528 I 14.09 755 I4.6O 1433 14.18 226 6 14.25 529 I 13.67 831 14.35 1434 14.58 235 2 14.36 525 2 14.14 834 14.36 1442 14-45 2 3 8 5 14.19 534 2 14-39 835 14.64 1443 14.09 239 i 14.74 556 3 14-34 837 4 14.57 1445 13.85 245 2 14.78 56i 2 13-86 838 5 14-39 1447 14.69 247 2 14-49 ; 562 I 14.62 [Zone t = 20 to 25. Mean Diurnal Motion = 14.16 0.038.] 3 3 14.59 224 2 14.23 696 I4.I4 1174 13.72 6 2 14.29 231 I 15.65 697 14.26 ii75 14.01 4 2 14.71 275 4 13-66 756 14.72 1225 I3.7I 29 2 14.49 336 i 14.07 757 14.60 1259 14.31 30 2 14.06 337 i I3.56 763 14-59 1260 14.72 30' I 14.66 340 i 12.94 777 2 13.38 1283 14.56 29' I 14.66 375 i I3.8I 2 14.03 1305 13.29 83' I 13-65 376 i 14-59 80^ I 14.21 1307 13.27 90' 3 13-80 377 i 14-59 806 I 14.11 1310 14-37 90" i 13-87 383 i 14.67 900 I 14.01 1311 14.27 118 6 13.62 384 i I3.8I 908 I I3.6l 1314 14.17 no 4 14.18 389 i 13.90 926 I 14.31 1320 13.88 89' 2 14-57 495 3 14.10 941 2 14.60 1328 13.34 121' 2 14.25 498 i 13.89 942 2 14-95 1330 13.01 135 3 13.91 54i 3 13.71 980 2 13.84 1346 14-34 137 I 14.57 540 2 13.91 1089 I I4.06 1385 2 14.05 139 2 14.24 582 2 15-79 1119 3 13.86 1386 2 14.15 140 140' 3 13.31 14.76 549 612 3 i 14-35 14.56 1127 1128 2 2 14.07 13-97 1387 1388 2 2 13.70 14.56 206 3 13-93 621 i 14-77 1144 I 13.08 1402 I 15.00 214 3 14.44 676 i 15.10 1150 2 14.06 1389 2 14.40 215 3 14.25 i FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 45 TABLE 2. Diurnal Motions Corresponding to each Five-Degree Zone. Continued. [Zone /== 20 to 25. Mean Diurnal Motion = 14.12 0.042.] Diurnal Diurnal Diurnal Diurnal No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. No. Days. motion, sidereal. II I 12.67 102' 2 14-69 462 3 14.43 66 5 13.90 22 3 12.07 1 60' I 13.94 463 I 14.22 666 13.90 47 3 13.71 160 3 13.24 502 I 14-35 667 14.40 45 3 14.10 180 13.86 503 I 14.55 691 14.71 59 3 13.63 187 14.48 536 I 14.39 692 14.37 59' 2 I4.OO 1 88 13-55 543 2 14.39 706 2 14.35 63' 2 13.93 189 I4.O6 591 3 14.56 7i7 2 14.40 65 3 14.07 190 13.73 597 2 14.15 836 4 14-45 69 3 13.40 237 5 I4.I8 598 2 14.50 8 4 7 I 14.64 ft 80' 69' 3 2 I I 14.66 14-43 14.03 I4.I8 239 246 267 269 i 4 3 i 14.74 14.43 14.69 13.86 604 605 606 648 I I I I 13.13 12.36 1440 14.51 856 858 86 3 14.17 14.34 14.70 14.17 94 4 14.12 270 3 14.32 656 I 14.40 888 14.50 95 4 14.08 278 2 14.19 657 I 14.90 889 14.22 97 6 13.91 279 2 14.52 661 I 14.00 1117 13-68 96' 4 14.42 274 2 14.67 662 I 14.30 1296 14.78 97' i 13.97 332 I 14.64 663 I 13.90 1297 14-68 102 4 14.00 392 I 12-53 664 I 14.30 1400 13.69 US 2 14.04 [Zone k = 25 to 30. Mean Diurnal Motion = 13.74 0.062.] 3' 3 13.64! 221 2 13.09 542 2 I3.8I 927 i I4.22 6' 2 14.07 222 2 12. 80 575 I 13.24 1091 i 15.29 181 I 13-55 334 I 14.07 685 2 14.35 II2O 2 13.82 i95 I 13-33 335 I 13.14 687 2 14-43 1286 I 13-53 196 I 13.46 517' I 12.75 698 I 14.03 1322 I 13.94 199 I 13.36 532 3 14.27 803 I 14.21 1332 I 13.78 200 3 13.07 539 3 14.10 804 I 14.00 1409 I 14.27 213 i 13-49 550 I 13.73 909 3 13.09 1410 I 13.51 220 2 13-37 i [Zone / = 25 to 30. Mean Diurnal Motion = 13.95 0.082.] 8 2 12.61 171 4 14.05 47i i 14.09 651 I 13.79 8' I 12. 6l 171' i 15.30 508 i 14.02 6 5 2 I 13.57 16 2 13.54 i 14.48 504 i 15.34 659 I 13.80 16' 2 13.19 186 i 13.60 537 2 14.30 660 I 14.30 38' I 13.09 250 2 13.96 538 I 14.10 707 2 14.88 38" 1 5 14.35 255 2 14.29 544 2 13.98 770 2 13.60 45" I 14.62 293 2 14.98 545 2 14.79 857 I 14.52 6/ 4 ' 14-39 294 2 14-73 546 2 13.29 1399 2 14.15 96 4 14.33 388 I H.53 616 I 13.56 1414 I 13.83 152 i 13.10 465 I 13.81 617 I 13.56 [Zone m = 30 to 35. Mean Diurnal Motion = 13.60 0.069.] 197 I 13.55 686 2 13-88 i 1023 2 13-35 1323 I 13.85 I 13.82 800 I 13.60 1090 I 13.53 1329 i ! 13.89 288 2 14.57 802 I 13.60 1263 I 13.60 1356 3 i 13.67 517 2 13.40 | 1022 2 12.82 1285 I 12.73 1357 3 13-99 569 I 13.43 ; [Zone w = 3o to 35. Mean Diurnal Motion == 13.79 0.124.] 64 3 14.26 153 4 14.10 464 I I3.8I 626 i 12.84 64" i 13.91 157 2 14.96 466 I 12.76 653 i 13.98 151 2 13.96 170 I 13.23 610 I 14.29 1406 2 13.35 THE ROTATION PERIOD OF THE SUN AS DETERMINED DISTRIBUTION AND AREAS OF THE FLOCCULI. No very minute flocculi were measured in this investigation. The best- defined points, which showed the least change from day to day, were selected for measurement. In many cases these points were chosen in the outlying portions of large groups of flocculi; in others they represented the centers of smaller compact masses. In all cases, however, the measures relate to the coarser flocculi. They therefore afford no evidence as to the motions of those minute flocculi, not exceeding a second of arc in diameter, which are shown on the best plates obtained with the Rumford spectroheliograph or the 5-foot spectroheliograph of the Mount Wilson Solar Observatory. The approximate distribution and area of the principal flocculi on the Sun during the period of this investigation were determined as follows: The globe, as already stated, is ruled with meridians and parallels i apart, the 10 lines being strengthened. In the squares thus formed, 10 on a side, the areas of the flocculi were estimated by counting the number of i squares covered by them. A sample record for the first plate is given below. TABLE 3. Longitude. Latitude. East of central meridian. West of central meridian. Total in 30 to 20 20 tO IO 10 too o to 10 10 tO 20 20 tO 30 zone. 40 to 30 3 7 9 o 3 3 25 30 20 4 II 17 "5 4 8 2 46 20 10 2 4 8 1 i 3 I IQ 10 4 4 i 6 4 i 2 16 tO -10 6 2 5 fi c 3 i I 18 10 2O 7 3 4 i 14 5 34 2O 30 4 4 14 17 10 10 59 -30 -40 i 5 I 2 6 15 East. West. Only a limited area of the globe was used, but the results obtained from the considerable number of plates employed should be fairly representative. The last column of the above table gives the total area of the flocculi in each 10 zone. In table 4 these results are brought together, and the grand total for each zone is given. These totals have supplied the data for platting the curve shown in fig. 4. The curve at the opposite limb of the Sun on this plate shows the number of the flocculi in the various zones measured in determining the rotation periods. The scale of the ordinates of this curve is i inch to 250 points measured. It should be remembered that in view of the varying density and contrast of the plates, and the great range of brightness of the flocculi, such estimates FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 47 of areas are necessarily very rough. They may serve, however, to give an idea of the distribution of the flocculi measured, and the approximate area occupied by them. N Distribution of points in floccuU measured for rotation periods. Areas, in, square d&jrees, covered by flocculi. & ^ FIG. 4. DISTRIBUTION AND AREAS OF THE FLOCCULI. TABLE 4. Areas of the Flocculi. Plate No. +40 to +30 +30 to +20 + 20 to + 10 +10 to o to 10 IO to 20 20 to -30 30 to 40 Plate No. + 4 o to +30 +30 to +20 +80 to + 10 +10 to o to IO 10 to 20 20 to -3 3 o to 40 2401 25 4 6 19 16 18 34 59 15 3204 8 19 42 6 41 13 I I *2407 ^207 8 28 GO 181 60 7 *T V / 2421 20 33 44 18 21 08 40 8 O v / 3211 7 20 27 68 31 216 81 / 5 2429 16 5i 66 29 7 6 63 83 9 3214 2 II 20 57 27 159 58 i 2442 7 67 25 77 221 57 8 3216 6 25 108 51 47 27 5 2452 5 15 84 21 80 238 40 14 3218 6 IO 43 85 19 50 34 3 2465 2 19 125 22 64 214 08 15 3221 4 8 36 30 28 22 2 2471 9 20 138 13 62 77 15 3223 i n 31 26 29 124 27 I 2482 7 15 112 12 58 86 79 14 3228 6 21 32 23 36 123 12 I 2496 5 18 III 30 18 10 60 7 3232 2 12 25 17 43 130 13 I 2501 i 22 94 55 31 43 38 3239 II 23 20 27 16 25 7 2521 5 37 109 44 40 114 29 8 3241 8 29 50 32 19 18 14 2 2542 i 29 37 13 8 78 23 i 3245 16 16 53 23 22 5 7 2558 o 24 22 12 20 3 3247 6 13 92 40 20 13 4 2560 i 25 33 22 8 27 14 2 3253 9 22 57 44 31 37 7 I 2569 II 39 28 13 66 16 17 3258 6 20 59 35 24 46 4 5 2580 3 9 5 6 24 108 63 22 3265 3 9 16 28 23 29 10 i 2588 3 9 n 17 3i 185 104 39 3272 12 20 29 44 41 36 2 2500 5 33 35 37 29 173 141 36 3279 9 21 46 60 22 19 2 2598 6 64 17 9 5 29 32 12 3284 5 18 42 77 24 35 4 2617 n 82 16 4 13 I 3286 II 63 47 30 IOO 16 2 2619 4 39 22 7 18 68 15 5 3293 7 16 66 64 49 no 58 I 2628 I 15 68 9 47 123 40 4 3295 9 19 55 35 16 53 24 O 2634 4 86 8 41 172 6 3300 12 14 39 112 19 47 32 I 2639 i 6 106 13 42 138 82 3 3303 4 7 30 117 21 48 ii 3 2651 3 15 72 17 52 56 14 3308 5 17 66 119 30 32 8 2 2675 8 14 40 30 22 58 26 13 33io 4 12 58 85 38 61 12 2681 7 27 63 21 102 IOI 32 14 3315 6 15 36 49 57 136 16 2 2694 5 34 53 26 73 51 24 2 3319 i 15 40 64 144 9 2699 2 8 21 16 68 171 33 3 3320 16 31 43 59 34 136 9 2 2712 9 28 33 24 61 80 n 6 3326 23 25 34 47 86 12 6 *2722 3333 22 31 126 19 13 12 6 i 2741 5 7 48 43 18 7 12 7 3338 13 22 no 22 35 22 5 2756 6 17 25 7 16 n 16 i 3348 39 57 88 35 46 23 12 I 2787 2791 2 2 4 IO 5 12 18 15 42 38 29 22 20 38 32 34 52 29 44 38 9 14 7 3354 ?M 16 16 10 43 44 24 64 67 40 26 28 35 34 20 2O 17 14 33 44 38 3 5 2 2797 6 13 33 18 30 18 7 3374 7 27 35 27 II 14 2 2800 2 10 21 14 25 71 21 7 3382 12 22 82 57 31 36 15 5 2809 6 15 16 7 27 112 6 3388 5 23 129 H3 23 33 23 i 2812 3 13 II 7 13 III n 6 3394 6 89 88 27 43 34 4 28l8 9 66 25 27 13 35 34 5 3398 3 9 95 92 24 77 35 9 2821 7 78 90 38 16 33 21 6 3405 13 17 69 73 15 27 12 2829 5 61 132 17 ^ 68 12 8 5 16 75 61 14 47 8 5 2831 4 25 105 25 6 63 16 8 3417 9 20 68 60 37 83 13 4 2839 2 9 67 6 7 58 II 10 3424 20 28 35 21 52 14 2 2870 4 9 3 n 14 48 13 6 3429 18 14 25 114 18 43 28 6 2877 i 5 4 14 13 46 17 6 3439 30 33 49 127 24 22 4 2 2880 i 4 4 13 n 46 18 6 3441 24 29 56 116 38 24 25 2 *2888 3447 ii 23 21 18 27 36 18 2 2898 i 30 72 6 21 23 12 14 O*T*T/ 3453 18 *o 32 40 25 30 _/ w 25 8 I 2904 2 18 60 45 29 22 16 9 3456 16 38 42 12 II 17 9 3 3020 5 17 14 24 54 25 14 3462 17 32 32 17 24 22 12 4 3028 I 2 60 13 27 59 23 24 3464 13 21 25 13 23 26 6 2 3062 2 12 22 27 14 63 44 3 3467 19 22 99 90 37 18 21 2 3069 6 29 26 12 15 44 32 3 I 3473 n 25 104 67 13 2O 20 5 3079 4 2O 19 12 10 46 22 5 3476" 13 28 41 21 13 69 10 4 3082 3093 i 2 II 23 II 27 10 55 9 31 33 24 44 7 2 ! 3479 | 348i 14 12 18 23 21 19 18 12 n 16 63 8 14 3 5 3101 I 7 47 69 74 40 6 3488 15 27 23 36 66 27 12 8 3104 6 6 73 23 26 15 n 3 3493 14 28 17 33 64 41 23 10 3106 3 12 103 18 38 19 6 3498 13 32 22 43 55 36 15 14 3112 i 14 32 21 46 22 IO i 3503 9 15 27 17 16 16 6 3H7 4 50 21 55 24 7 2 3507 IO 19 49 24 10 17 8 4 3121 2 31 15 30 22 16 6 3509 8 18 49 32 14 22 10 3 3185 8 20 IOI 40 36 32 32 7 2 15 37 45 14 26 20 3 3190 22 138 30 56 15 7 i 3528 3 9 25 24 13 27 16 4 3191 10 29 85 30 T C 45 23 18 M 2 3533 4 16 34 14 19 9 5 3201 10 17 42 J 5 II 29 II I I Total 987 3519 6772 4827 4073 8576 3529 738 * Not measured. FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 49 DISCUSSION OF THE RESULTS. The mean values of the diurnal motion for each zone of 5, with the com- puted probable errors and the weights, are brought together in the following table. The weighted means for corresponding zones in north and south latitudes, together with their probable errors, are also included. TABLE 5. * North. Weight. South. Weight. Weighted mean. o to 5 5 10 14. 72 0.03 1 14.50 .027 156 196 I4.57 0.045 14-55 .030 103 2O2 14.66 0.026 14.52 .020 10 15 14.34 .024 208 14.39 .020 323 14.37 .Ol6 15 20 14.14 .025 222 14.30 .028 240 14.22 .019 20 25 14-13 .035 143 14.11 .038 144 14.12 .026 25 30 13.74 .060 51 14.03 .073 66 I3.OO .049 30 35 13.64 .073 26 13.93 -120 20 13.76 .067 A comparison of these results with those of Carrington, Spoerer, and Maunder for spots, StratonofT for the faculae, and Duner and Halm for the reversing layer (iron lines), is given in fig. 5. Numerical comparisons are also given in the following pages. Before proceeding to these comparisons, it should be remarked that the large proper motions of the calcium flocculi must always stand in the way of very accurate results, unless a much greater number of observations than those here included are available. 27.5 27.0 2*5 26.0 25.5 25.0 245 24.0 ; FIG. / //, f \ 7 j. TJ V / // .,- -'" / / f ^ T/ / s ^\ / >*' + ^ ' J ' . X I, --/, .... ,' * / ,. ?* X i / X s , / sS' ' / / / _^ ^ / -?'* ^ A ./?- ..- ;/; >'' ^ -^ *" " & n sp< in 8P< >ts(Ca rts(Sp ring* oerer n) .3 R R versii sverii ^lay I?'Y r(Dun8'r) sr( Halm 190 -02) - R .verai, **y ir(H|m 19( 3) > &' W 13 ZO" 25* 30 35* 40* 45 5. THE ROTATION OF THE SUN AS SHOWN BY THE MOTIONS OF THE SPOTS, FACUL FLOCCULI, AND REVERSING LAYER. 50 THE ROTATION PERIOD OF THE SUN AS DETERMINED As the result of a long series of Sun-spot observations, Spoerer derived the following empirical formula, as best representing the diurnal motion of the spots in any latitude: = 8.548 + 5.798 cos Computing the values of corresponding to = 2.5, 7.5, 12.5, etc., and comparing the results with those we have obtained for the calcium flocculi, we have: TABLE 6. Spoerer, spots Flocculi. Flocculi minus spots. oto 5 14-34 14.66 0.32 5 10 14.30 14.52 0.22 10 15 14.21 14-37 0.16 15 20 14.08 14.22 0.14 20 25 13.90 14.12 0.22 25 30 13.69 13.90 0.21 30 35 13.44 13.76 0.32 According to Spoerer's results, it would thus appear that the flocculi move more rapidly across the disk than the spots. The gain in 24 hours, taking the mean without regard to latitude, is about 0.2. However, this conclusion is not borne out by Mr. and Mrs. Maunder's extensive investigation of the Greenwich Sun-spot measures for the two complete cycles i879-i9Oi. 10 The results of this investigation, for the zones covered by our observations, are given in the following table: TABLE 7. Greenwich spots. Flocculi. Flocculi minus f spots. 2.5 14.61 14.66 0.05 7.5 14.50 14.52 0.02 12.5 14.44 14.37 -0.07 17.5 14.38 14.22 0.16 22.5 27.5 14.14 13.78 14.12 13.90 0.02 O.I2 32.5 14.07 13.76 -0.31 StratonofFs study of the solar rotation is based upon the measurement of the heliographic positions of faculse photographed at Pulkowa, during the years 1891-94." Wilsing had previously investigated this subject, with the aid of photographs made at Potsdam in 1884, and found for the faculae a velocity of 14.27 in 24 hours, constant for all latitudes. This unexpected result caused Belopolsky to attack the problem. Although he measured only a small number of photographs, he was able to detect the fact that the " The Solar Rotation Period from Greenwich Sun-spot Measures from 1879-1901." Monthly Notices, June, 1905. 11 Stratonoff : " Sur le Mouvement des Facules Solaires." Memoir es de V Academic Imperiale des Sciences de St.-Petersbourg, VIII Serie, 1896. FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 51 faculae in high latitudes rotate in a longer period than the spots at the equator. Stratonoff, with a much larger amount of material at his disposal, undertook to determine the law of rotation of the faculae as a function of the latitude. 2,245 measures were made of 1,062 faculae on 234 plates. As it was never possible to follow a facula more than four days from the limb, the measures were necessarily made on the least favorable part of the solar surface. In spite of this fact the following very satisfactory results were obtained. Our corresponding values for the flocculi are given for comparison. TABLE 8. * North. I No. of obser- vations. South. I No. of obser- vations. Faculae, means. s Flocculi, means. Faculae minus flocculi. to <5 14.62 Q 14 62 0.127 14 66 o 026 o 04 5 10 10 15 15 20 20 25 25 30 30 35 -zc 40 T";: 14.61 14.34 14.14 14.21 13.97 13-50 39 125 no 124 109 15 14-63 14.26 14.21 14.17 I4.2O 13.65 n.6i 6? 124 137 101 34 24 14.61 0.061 14.31 0.044 14.18 0.036 14.19 0.036 14.08 0.040 13.60 0.059 13.61 0.086 14.52 0.020 14.37 0.016 14.22 O.OI9 14.12 0.026 13.90 0.049 13.76 0.067 0.09 0.06 O.O4 O.07 0.18 0.16 It appears from the table that the observed differences in the daily motion of the faculse and flocculi are of the same order as the probable errors, except in the higher latitudes, where the observations are few and the results uncertain. Let us now consider whether the daily motion of the flocculi decreases at a uniform rate in passing from the equator toward high latitudes. For com- parison, we also include StratonofFs results for the faculae. The quantities in the columns A are obtained by subtracting the value of for each zone from the value of in the zones +5 5, which we take as the standard velocity. TABLE 9. Faculae. Flocculi. North. South. Mean. North. South. Mean. 5 to io 0.01 0.01 0.01 0.16 0.11 0.14 10 15 0.28 0.36 0.31 0.32 0.27 0.29 15 20 0.48 0.41 0.44 0.52 0.36 0.41 20 25 0.41 o.35 0.43 0.53 0.55 0.54 25 30 0.65 0.42 0.54 0.92 0.63 0.76 30 35 31: AQ 1. 12 0.97 I 01 1.02 I 01 i. 02 o.73 0.89 It thus appears that the acceleration is very nearly uniform. Indeed, the entire series may be fairly well represented by a straight line, since the larger deviations can be given little weight, as they correspond to zones in which few observations are available. 52 THE ROTATION PERIOD OF THE SUN AS DETERMINED An interesting investigation of the rotation period of the Sun, based upon the motion of large groups of faculse, is that of Wolfer." He found that during the period in question (1887-90) there were two persistent groups of faculae, of great size, on the Sun, about 180 apart in longitude. Each group showed a gradual increase in longitude, which continued during the entire period. As the longitudes were based upon Spoerer's mean daily value of 14.2665, derived from observations of the spots, it follows that the faculae were moving more rapidly than the spots, if we may assume that Spoerer's mean daily value can be depended upon. Maunder's results, how- ever, as already remarked, throw doubt on this point and the question can not at present be regarded as settled. Let us now compare our results for the flocculi with those of Duner for the reversing layer. Duner's determination of the solar rotation was made by measuring the double displacement of two iron lines, A 6301.72 and A 6302.72, referred to neighboring telluric lines. The radial velocities found for different latitudes therefore represent the motion of the iron vapor in the reversing layer. Duner's observations correspond to the latitudes 0.4, JS-O , 30-i j 45-0, 60.0, and 75.0. In order to obtain velocities corre- sponding to the mean latitudes of our zones, Duner's formula II, adapted from Spoerer's formula for the spots, has been used. 13 The values of have thus been obtained by substituting 2.5, 7.5, 12.5, 17.5, 22.5, 27.5, and 32.5 for < in the formula: | = 8.564 +6.153 cos < TABLE 10. Reversing layer. Flocculi, means. Reversing layer minus flocculi. oto 5 I4.7I 14.66 0.05 5 10 14.66 14.52 0.14 10 15 14-57 14-37 0.20 15 20 14.43 14.22 0.21 20 25 14.25 14.12 0.13 25 30 14.02 13.90 0.12 30 35 13.75 13.76 0.01 So far as can be judged from this comparison, in all latitudes excepting the highest, which is of low weight in the flocculi determinations, the reversing layer gives higher velocities than the calcium flocculi, the average difference in the value of amounting to about 0.014. Since the corre- sponding difference in the case of Spoerer's spots is about 0.2, and of opposite sign, the Sun would appear to have a gradually increasing rotational velocity in the order spots, faculae and flocculi, reversing layer, were it not for Maunder's results. 13 A. Wolfer: " Zur Bestimmung der Rotationszeit der Sonne," V. J. S. d. zurch. naturforsch. Ges., Bd. 41. 13 Astronomische Nachrichten, No. 3994. FROM THE MOTIONS OF THE CALCIUM FLOCCULI. 53 It is an interesting question whether the apparently greater velocity of the iron vapor in the reversing layer, as compared with the faculse and flocculi, is genuine. The average results of Halm's observations, covering the period 1901-06, would point to a contrary conclusion. They are given in the following table, extracted from his more complete table in Astronomische Nachrichten, No. 4146. TABLE n. Linear velocity. No. of obser- vations. Daily motion. 1 Linear velocity. No. of obser- vations. Daily motion. 2.3 2.042 km< 103 14.55 21.4 .856 im - 43 14.19 6.6 2.032 09 14.56 24.5 .788 55 13.98 9.4 2.OO2 65 14.44 27.6 755 53 14.09 12.4 1.972 44 14.37 30-7 .657 4i 13.72 15-6 18.4 1.952 1.907 8 14.42 14.31 .596 .561 45 5i 13-59 I3.8I These results differ decidedly from DuneYs, especially in the lower lati- tudes (see fig. 5). It may be added, however, that an unpublished series of measures by Adams, covering the period June 1906 to February 1907, gives results in very close agreement with Duner's, up to a latitude of 45. Beyond this point the reductions are not yet complete. The very high pre- cision of Adams's measures lends great weight to his confirmation of Duner's results." We do not attempt to discuss here the unsettled question of a possible variation in the rotational velocity of the Sun, indicated by Halm's measures for 1901-02 and 1903. The apparently high accuracy of Halm's results appears favorable to his conclusions, but it must remain for the future to prove whether such variations actually occur. It can not be said from the comparisons given above that a systematic difference of velocity of various classes of solar phenomena has been demon- strated. So far as the flocculi are concerned, no very general discussion of their motions could be based on the restricted materials now available. We are both engaged in work with powerful instruments, which furnish larger solar photographs, much richer in detail and better suited for measurement than the Kenwood plates. We accordingly expect to return to this discussion, with the advantage afforded by a longer series of better observations. A more general consideration of the problem of the solar rotation, and a more accurate estimate of the weight to be attached to measurements of the velocity of various classes of phenomena, should then be practicable. 14 Since this paper was put in type the following articles on the solar rotation have appeared in Contributions from the Mount Wilson Solar Observatory, Nos. 20, 24, and 25. Spectroscopic Observations of the Rotation of the Sun. By Walter S. Adams. Astrophysical Journal, XXVI, November, 1907. Preliminary Note on the Rotation of the Sun as Determined from the Displacements of the Hydrogen Lines. By Walter S. Adams. Astrophysical Journal, XXVII, April, 1908. Preliminary Note on the Rotation of the Sun as Determined from the Motions of the Hydrogen Flocculi. By George E. Hale. Astrophysical Journal, XXVII, April, 1908. 54 THE ROTATION PERIOD OF THE SUN. FUTURE STUDIES OF THE SOLAR ROTATION. > A general attack on the problem of the solar rotation calls for the co-oper- ation of several observatories. It should include: 1 i ) Further investigations of the motions of individual spots, closely con- nected with: (a) simultaneous determinations of their level, made with the spectroheliograph; (b) their appearance at and near the limb (visibility of umbra, etc.), also bearing upon the question of level; (c) their spectra, including general absorption, and relative intensity of lines, 15 bearing on their temperature and level ; (d) measures of the solar activity, particularly in the zone occupied by the spots in question. (2) A continuation of Maunder 's work on spot motions. (3) A continuation of StratonofFs work on the motions of the faculse, using such means of increasing contrast as will permit the inclusion of faculse near the center of the Sun. (4) Investigations with the spectroheliograph on the motions of (a) the bright regions photographed with the H t or K lines ; (b) the H 2 or K 2 calcium flocculi; (c) if possible, the H 3 or K 3 dark calcium flocculi; (d) the hydrogen flocculi; (e) the iron flocculi, and those of other gases. (5) A continuation and extension of the spectroscopic work of Duner and Halm, on the motion in the line of sight of the reversing layer at opposite limbs of the Sun. This investigation, which would neces- sarily require the co-operation of several observatories, should pro- vide for the employment of certain lines in common by all observers. It should also involve the use, by each observer, of certain additional lines, chosen so as to include: (a) a considerable number of lines in the spectrum of at least one substance ; (b) lines representing ele- ments of high, medium, and low level; (c) lines enhanced in the spark, and those strengthened at low temperatures. (6) An investigation of the motion in the line of sight of the lower chromosphere (or reversing layer), through spectroscopic observa- tions of the relative displacements of bright lines at opposite limbs of the Sun. (7) A determination of the motion in the line of sight of quiescent promi- nences, in various latitudes and at various heights above the limb. SUMMARY. This investigation of the motion of the calcium flocculi has led to the following conclusions : 1. The rotation periods for different latitudes show the existence of an equatorial acceleration, similar to that previously observed in the case of Sun-spots, faculse, and the reversing layer. 2. In approximate terms, the acceleration varies uniformly with the latitude. 3. The average daily motion of the calcium flocculi is of the same order as that of the spots, faculse, and reversing layer. The differences among the rotation periods obtained by various observers are so marked that no definite conclusions can yet be drawn as to the relative velocities of these different phenomena. "See Hale, Adams, and Gale. "Preliminary Paper on the Cause of the Charac- teristic Phenomena of Sun-Spot Spectra." Astrophysical Journal, October, 1906. UNIVERSITY OF CALIFORNIA LIBRARY BERKELEY Return to desk from which borrowed. This book is DUE on the last date stamped below. ASTRONOMY LIBRARY D 21-95m-ll,'50(2877sl6)476