4o6 



NATURE 



[February 21, 1901 



HARVARD COLLEGE OBSERVATORY. 



THE fifty-fifth annual report of the work done at the Astro- 

 nomical Observatory of Harvard College during the year 

 ending September 30, 1900, has recently been circulated by the 

 Director, Prof. E. C. Pickering, and is here summarised. 



Observatory Instrtimenls : East Equatorial. — The obser- 

 vations with this instrument were made by Prof. O. C. Wendell ; 

 during the year 24,000 photometric light-comparisons were 

 made, principally with the achromatic prism polarising photo- 

 meter. Over 15,000 of these were series of measures of twenty 

 variables. 



This instrument, with a second photometer adapted to stars 

 nearer together, has been used for determination of the follow- 

 ing :— 



Comparisons. 

 Ceti ... .. 1792 



U Camelopardali. 160 



j3 Lyrae... 

 Nova Aurigse 



Comparisons. 

 ... 848 

 ... 96 



and also in the photometric measurement of Jupiter's satellites 

 while undergoing eclipse, eighteen eclipses having been observed ; 

 the satellites of Saturn, Japetus and Titan ; the light of the 

 planet Eros (224 settings), and in addition the systematic 

 photometric observations of variable stars of long period have 

 been continued. 



Meridian Circle.— The. ruled glass plate with which former 

 determinations have been made for the last ten years has been 

 replaced by spider lines, and the declination micrometer em- 

 ployed in conjunction for the first time. From the new 

 observations a comparison is to be made between the accuracy 

 obtainable by the two methods. The work of the instrument 

 has been mainly confined to determinations of clock error and 

 instrumental constants. The reduction of the observations made 

 by the late Prof. Rogers from 1879- 1883 is being continued. 



12-inch Meridian Photometer. — ^ With this instrument 79,024 

 settings were made by the Director on I40 nights. The first 

 large work, comprising the observation of all the stars contained 

 in the Durchmusterung, in zones 10' wide and 10° apart, is now 

 practically completed ; the total number of stars is 9233, 6195 

 of which are fainter than the ninth magnitude. Good progress 

 has been made with the reductions. 



Meridian Photometer. — The observations of the stars south of 

 declination -30°, of magnitude 7"0 and brighter, were com- 

 pleted early in December at Arequipa. Forty-four series were 

 taken, involving 13,244 settings. The instrument was then sent 

 to Cambridge, mounted, and electric light substituted for gas. A 

 catalogue of standard stars, one in each 10° square, has now 

 been prepared, and 16 series, including 6424 settings, have been 

 made by Prof. Bailey. 



Henry Draper Memorial. — Six hundred and eighty-nine 

 photographs have been obtained with the 11 -inch Draper tele- 

 scope, and 2187 with the 8-inch instrument. The examination, 

 by Mrs. Fleming, of the spectra on these plates and on those 

 taken with the Bruce and Bache telescopes has led to the 

 discovery of fourteen new variable stars, ten of which contained 

 bright hydrogen lines in their spectra, and six are gaseous nebulse. 

 Eight variables have also been discovered in other ways. A new. 

 star in Aquila was found from examination of photographs, 

 making the sixth object of this class detected in this manner. 



In the study of the spectra of bright southern stars, it has 

 been found that Hj8 is bright in A.G.C. 8991, and variable 

 in the two stars A.G.C. 19737 {f\ Centauri), and A.G.C. 20,878 

 (<f- Apodis). 



Experiments are in progress for determining the photographic 

 magnitudes of stars by the measurement of images out of focus, 

 whereby a comparison is made of surfaces instead of points. It 

 is found that stars can be measured in this way at the rate of five 

 a minute, with a probable error of a tenth of a magnitude. 

 Some 14,000 measures have been made in this way. For special 

 purposes, charts are now being regularly taken with the 8-inch 

 and ii-inch Draper telescopes, without following, by varying the 

 rate of the clock and the position of the polar axis. A small 

 telescope is rigidly attached to the base of the 11 -inch telescope 

 and directed toward two distant scales placed at right angles to 

 each other, thereby permitting the axis to be set in any desired 

 position rapidly and accurately. A photograph of the planet 

 Eros was oVjtained in this manner on July 28, 1900, in which the 

 image was sensibly round, although the exposure lasted 153 

 minutes. 



Photographs of star occultations and eclipses of Jupiter's satel- 

 lites have been obtained on several occasions. 



NO. 1634, VOL. 63] 



Boyden Department. — As the sky was so clear at Arequipa 

 during the latter part of 1899, it was unnecessary to remove the 

 meridian photometer to the Desert of Atacama, Chile, as had 

 been anticipated. Great delay has been experienced in the 

 transmission of the plates to and from Peiu, partly due to the* 

 quarantine consequent on the prevalence of fever along the west 

 coast. The number of photographs taken with .the 13-inch 

 Boyden telescope is 201, and with the 8-inch Bache 2054. 



Three hundred and fifty-eight visual observations of 48 

 southern variables have been made by Argelander's method. 

 Systematic examination of all the stars south of declination 

 -30°, between the magnitudes 6 '3 and 7*0, inclusive, for the 

 detection of new double stars, has been continued ; 541 stars 

 have thus been examined, leaving a further 450 requiring 

 observation. 



Meteorological Observations. — Observing stations have been 

 maintained during the year at eight localities having altitudes 

 varying from 100 to 19,200 feet ; but great difficulty has been 

 experienced at the lofty mountain stations. 



These observations have now been continued for eight or nine 

 years ; taking into consideration, however, the striking uni- 

 formity of conditions which prevail in different years in this 

 region, it is probable that additional observations would not 

 greatly increase knowledge, and it has therefore been decided 

 to suspend the meteorological observations of all the stations, 

 except those at Arequipa. This seems to be a great pity, for 

 nine years is a very short period when meteorological data are 

 in question, and especially when the altitudes of the stations are 

 so different. 



The Bruce Photographic Telescope. — Seven hundred and sixty 

 plates have been taken with this instrument during the year. 

 From 319 of these 198 new faint nebulae have already been 

 detected. On these plates thus examined have also been found 

 92 asteroid trails and 2 meteor trails. In the spring of 1900 

 successful photographs of Eros were obtained by a special 

 method when the object was too faint for ordinary procedures. 

 The photographic plate was moved during exposure at the rate 

 calculated for the motion of Eros relative to the diurnal motion. 

 Three good plates were thus obtained on April 28, 30, 31, 1900. 



A long" series of photographs of Saturn was taken, to deter- 

 mine, if possible, the orbit of the satellite Phoebe. From an 

 examination in Arequipa the existence of this object has not been 

 confirmed ; a careful examination will again be made on the 

 arrival of the plates at Cambridge. 



Blue Hill Observatory. — The chief work here has been the 

 continuation of the exploration of the upper atmosphere by 

 means of self-recording instruments carried by kites. The 

 greatest height attained was 15,800 feet. 



Miscellaneous. — (i) The scheme of distribution of important 

 astronomical news is now greatly appreciated. Twenty bulletins 

 have been issued during the year. These are sent gratuitously 

 to all who desire them, and telegrams will be sent on payment 

 of official fees. 



(2) The long focus telescope obtained last year, with aperture 

 of 12 inches and focal length of 136 inches, was lent to Prof. 

 Langley, of the Smithsonian Institution, for photographing the 

 corona during the eclipse of the sun in May 1900, the results 

 being highly satisfactory. 



(3) By the aid of an appropriation from the Rumford Fund 

 of the American Academy, an important investigation has been 

 started for the determination of standards for faint stellar mag- 

 nitudes. For this work telescopes of 40, 36, 26, 15 and 12 

 inches aperture will be used, by the generous co-operation of 

 the Yerkes, Lick and McCormick observatories with that of 

 Harvard. 



(4) A considerable number of photographs of the planet Eros 

 have been taken,, but as it is considered that the present oppo- 

 sition will not afford improved values of the solar parallax, it is 

 doubtful if they will all be measured, unless the number ob- 

 tained elsewhere be insufficient. Considerable care will, how- 

 ever, be taken in determining the variations of the light of the 

 planet, both photographically and visually. 



Establishment. — Prof. Pickering marks the completion of the 

 work of the Observatory for the nineteenth century by giving 

 a detailed account of the needs of the institution and the 

 conditions of those portions of its work which are at present 

 unfinished. The annual income is nearly 10,000/., but this is 

 required for current expenses. The estimated value of the 

 buildings and instruments at Cambridge is about 15,000/., and 

 at Arequipa about 12,000/. 



