572 



SCIENCE 



[N. S. Vol. XLIV. No. 1138 



ham has played in this movement. He has 

 planted in two of our great observatories a 

 tradition of faithful observing that will long 

 endure; and from these two institutions the 

 same tradition has been transplanted to 

 smaller and to newer observatories. We are 

 reminded of this by Professor Fox's dedica- 

 tion of this first volume of annals from the 

 Dearborn Observatory : " to Sherburne Wesley 

 Burnham, who spared not himself in his oft 

 heroic vigils, whose personal encouragement 

 has been the direct inspiration for these ob- 

 servations." These words might have been as 

 fittingly written by many another astronomer. 



Only a few of the world's great telescopes 

 are used to their full capacity, and most of 

 these few are to be found on this side of the 

 Atlantic. Among them must now be counted 

 the Dearborn telescope, which has been used 

 whenever the sky has permitted on almost 

 every night since the fall of 1909, a date that 

 marks the advent of the present director. 

 This is a remarkable record, for during most 

 of this time Professor Pox has worked single 

 handed, and at no time has he had more than 

 one assistant. Moreover, in addition to his 

 work at the telescope he has fulfilled various 

 administrative duties and has taught classes 

 at the Northwestern University. It is clear 

 that the Dearborn telescope, though it is a 

 beautiful and efficient instrument, is not at 

 present the chief asset of the Dearborn Ob- 

 servatory. 



The introduction to this volume contains an 

 historical account of the observatory, begin- 

 ning with the formation of the Chicago Astro- 

 nomical Society in 1862, the purchase imme- 

 diately afterward of the 18j-inch telescope, 

 the early struggle for existence, the almost 

 fatal blow dealt by the great fire of 1871, and 

 finally the happy affiliation in 1887 with the 

 Northwestern University. The telescope was 

 for a time not only the largest in the world 

 but probably also the finest. Its excellent 

 qualities have been proven by the discovery of 

 the companion to Sirius (while still in the 

 hands of its makers, Aivin Clark and Sons) ; 

 by a long list of measures of difficult objects 

 by Burnham, Hough and Pox; by the excel- 



lent photographs that have recently been made 

 with it; and most convincingly of all, by the 

 results of an application to it of the Hart- 

 mann tests. Professor Fox carried out these 

 tests in 1912 and 1913 and describes them fully 

 here. They show that when the objective is 

 at its best there is practically no spherical 

 aberration. They also indicate that under 

 certain temperature conditions a considerable 

 amount of aberration may be temporarily 

 present, the effect being similar to the phe- 

 nomena that the reviewer showed to exist in 

 the case of the Thaw telescope at Allegheny 

 and in one or two other very large refractors. 

 This effect is correlated, not directly with the 

 actual temperature, but rather with the rapid- 

 ity with which the temperature has changed 

 in the interval immediately preceding the ma- 

 king of the test. 



Two chief investigations are now being car- 

 ried out with this telescope, the determination 

 of stellar parallaxes by photography, and the 

 systematic measurement of double stars. It is 

 to the latter that the present volume is de- 

 voted. The random discovery of new double 

 stars or the casual measurement of the best 

 known doubles, does not add much to the 

 progress of this branch of astronomy. Pro- 

 fessor Pox has wisely adopted an observing 

 program made up of definite lists of stars that 

 would not be likely to receive attention other- 

 wise. The volume before us is chiefly con- 

 cerned with the double stars discovered by 

 Holden, with those discovered by Kiistner, 

 and with a selected list from Burnham's Gen- 

 eral Catalog. Much care was expended on 

 the arrangement and printing of the observa- 

 tions, so that the volume is not only a beau- 

 tiful example of the printer's art, but is one 

 that leaves nothing to be desired on the score 

 of convenience of reference. 



Some of the pairs in this volume were meas- 

 ured not only with the Dearborn telescope, 

 but earlier also with one or both of the Terkes 

 refractors of 12 and 40 inches aperture, respec- 

 tively. The comparison of the measures of 

 the same object made by the same observer is 

 very instructive. The reviewer has collected 

 all such cases in the volume and has arranged 



