January 31, 1895] 



NATURE 



329 



RECENT WORK AT HARVARD COLLEGE 

 OBSERVATORY. 



'PHE forty-ninth annual report of the [director of the Ila-varl 

 College Astronomical Observatory, by Prof. E. C. 

 Pickering, has come to hand. Omitting mitteri of administra- 

 tion and some of the details, the following summary ■^hows the 

 most important events of the year covered by the report. 



Photometric Observations. 



The reduction of the photometric measures of the southern 

 stars observed by Prof. S. I. Bailey in Peru, is now completed, 

 and the catalogue containing the resulting mignitudes is in 

 print. The observations of the first investigation undertaken 

 with this instrument since its return from Peru are nearly com- 

 pleted. About six thousand stars have each been observed on 

 at least three evenings. This catalogue includes all the stars of 

 the Harvard Photometry, eighty lists of comparison stars for 

 variables of long periods, and various stars the magnitudes of 

 which are desired by other astronomers. A study has been 

 made of the atmospheric absorption, especially for very low 

 stars, and its coefficient has been derived on each evening, both 

 for the southern and the northern stars. These values are now 

 applied as corrections to the individual observations, instead of 

 adopiing a mean value of the absorption. .\ new working list 

 has been prepared of the stars north of -40"* having -nagnitude^ 

 7'5 or brighter, and which have not alrealy b;en observed with 

 the meridian photometer. This list contains about fourteen 

 thousand stars, of which about two thousand have been observed 

 during the last year. 



Pr.jf. Pickering refers to Mr. S. C. Chandler's criticisms on 

 the photometric observations made with the meridian photo- 

 meter. [A^lron. A'ach. vol.cxxxiv. p. 355, and vol. cxxxvi. p. 85.) 

 It is maintained that the meridian photometer possesses the 

 same advantages in measuring the light of a star that the 

 meridian circle does in measuring its position. In both instru- 

 ments absolute values are determined directly, and they are 

 obtained very rapidly. Stars are identified in the same way 

 in both, rapidly and accurately, and in both the systematic 

 errors are small, even if the accidental errors are in some cases 

 larger than those resulting from other methods. S'.ars can be 

 observed with the meridian photometer under favourable cir 

 cumstances nearly at the rate of one a minute, and the average 

 deviation of the results thus obtained does not generally exceed 

 one-tenth of a magnitude. 



.\stronomicai. Photograph v. 



The number of photographs taken with the 8-inch Draper 

 telesco,ie is 1657. The number taken in Peru with the 8 inch 

 Bache telescope is 1708. All of the spectra photographed 

 with these instruments have been examined by Mrs. Fleming. 

 .\s a result seven variable stars, U Puppis, V Cancri, V L-^onis, 

 T Sagitlarii, R Delphini, K Vulpecula;, and R Phcinicis, 

 have been shown to have the hydro:;en lines bright in their 

 photographic spectra. Unsuccessful attempts have been made 

 to photograph the specira of many other variables of long 

 period when at maximum, and no image has been obtained. 

 This has been found to be due in many cases to large errors in 

 the ephemerides, and has tieen remedied by depending upon 

 the observations of Mr. VV. M. Reed, and making the time of 

 photographing each star depend u|)on its observed, instead of its 

 predicted, brightness. Eleven new variables have bf en discovered 

 in the year, from the presence of bright h)diogen lines in their 

 spectra, tiesides three the variability of which w?s discovered 

 from changes in their photographic images. The number of stars 

 of the fifth type has been increased by seven, making the total 

 number of these objects 62. Five nebii'a; have been discovered 

 from I heir spectra. The hydrogen line H j8 has been discovered to 

 be bright in the spectra of five stars, and twelve stars have been 

 shown to belong to the fourth type. The specira of .\. G. C. 

 18049 and 22640 are peculiar. Several photographs have been 

 obtained of the new star in the constellation Norma. At the 

 Lick Observatory it was shown from visual observations that 

 its spectrum, as in the case of the new star in Auriga, had 

 become that of a gaseous nebula. This has been confirmed 

 from photographs taken at .-Vrequipa, whiv;h also show that 

 this olijec is now gradually becoming fainter. The spectra of 

 4557 stars on thirty plates have been classified for iht new 

 Draper Catalogue. On one of these plates covering ihs region 



NO. 13x8, VOL. 5 I 



of the variable star tj Carinx, 1 161 spectra have been 

 measured. 



The number of photographs taken with the i l-inch Draper 

 telescope is 912. The lines in the spectrum of i Ursae Majoris 

 are found to be double in 59 out of 340 images, and of i3 Aurigae 

 in 47 out of £5. 



.\n investigation has been in progress for some time for the 

 detection of stars having large parallaxes or proper motions. 

 Phoographs are taken in the usual position with the dim to- 

 »ards the object glas--, and also with the pla'e reversed, the 

 photograph being taken through the glass. These are repeated 

 at intervals of six months at the times when the effect of 

 parallax on their right ascension would have its greatest value. 

 Plates thus obtained may then be superposed so that th-i fibus 

 shall be in contact, and the two images of each star made to 

 appear like a close diuble with components north and south. 

 SuitU changes in position miy be detected by changes in the 

 position angle, and the amount of the parallax or proper 

 motion may be measured with great accuracy. Several hundred 

 s'ars have thus been shown to have no parallax exceeding hilf 

 a second. 



OiisERVATiiiN IX Peru. 



The meteorological station on the summit of Misti, at a 

 height of 19,200 fee', was succes-fully conduced far several 

 months, one of the assistants, generally .Mr. Waterbury, visit- 

 ing it every ten days, and readjusting the self-recocling instru- 

 ments. Unfortunately, early in .September, the shelter con- 

 taining the instruments was found to have been broken into, 

 and a number of the instruments carried off. Apparently the 

 robbery was committed by two Indians, whose tricks were 

 followed to a considerable distance. The property stolen 

 would, of course, be of no u-e to the thieves, and its intrinsic 

 value would be a small part of the actual loss. The work at 

 this station was conducted with great labour ; a mule paih had 

 been built to the summit, and the entire expenditure had been 

 large. It will be a serious loss to science if it proves impossible 

 to maintain the station. 



The number of photographs obtained by Prof. Bailey with 

 the l3-inch Boyden telescope is 561, including some remarkable 

 charts. Among them may be mentioned photographs of the 

 Nebula of Orion with an exposure of eight hours, of the cluster 

 u'Centauri with an exposure of six hours, and of tj Carin.r; with 

 exposures of six and fourteen hours respectively. In some of 

 these, notwithstanding the long exposure, the image shows no 

 deviation from the circular form. This is mainly due to sub- 

 stituting for a finder two eyepieces attached to the main tele- 

 scope. One of them serves to follow a guiding star in the 

 usual way ; the other, directed to another star, shows if the 

 plate needs to be rotated in its own plane. This appears to be 

 an important improvement in making the best photographic 

 charts of long exposure, especially of the polar regions. By 

 the ordinary methods it is impossible to entirely correct such 

 errors as those due to flexure and refraction, which do not 

 depend upon the direction of the axis of the earth. 



Atteniion is again drawn to the importance of making 

 use of the admirable atmospheric conditions at Arequipa. .\ 

 telescope of the largest size would not only have most lavourable 

 opportunities for work, but a field unexplored with such an 

 instrument in the southern sky. Much could be done with a 

 smaller instrument, as is shown by the work already accom- 

 plished with the 13-inch Boyden telescope. Out of a list of 

 thirty telescopes having aperture exceeding 14 inches or more, 

 but one is mounted south of latitude -i- 35% and this one is not 

 in use. A moderate expense only would be recjuired to carry 

 out this plan. 



Work with the .New Telescope. 

 One of the most important events of the year was a careful 

 trial of the Bruce photographic telescope. Nearly a thousand 

 photographs have been obtained with it. The spectra of the 

 faint stars prove very satisfactory, and stars too faint to be photo- 

 graphed with the other instruments can thus be studied. Bright 

 hydrogen lines have been found in the spectra of S Orionis, 8 

 Bootis, W Virginis and S Librje, and the spectrum of V 

 Ophiuchi has been shown to be of the fourth type. The length 

 of these spectra is about a quarter of an inch, which is sufficient 

 to .show much detail in the spectra of fairly bright stars. To 

 study still fainter spectra a prism of crown glass and of smaller 

 angle has been ordered. T he absorjjtion of the photographic 

 rays is less for this material, and it is expected that much fainter 



