June i6, 192 i] 



NATURE 



503 



•sufficient to account for the properties of emulsions 

 prepared in different ways. The author treats of the 

 character of the developed image, and distinguishes 

 T)etween the graininess due to the individual particles 

 •of silver, the aggregations of these particles, and the 

 agglomeration of these primary aggregations. The 

 sharpness of the image is discussed, curves showing 

 the quantitative values of these properties are given, 

 and the methods by which these properties have been 

 investigated are described. 



Year Book No. 19 of the Carnegie Institution of 

 Washington contains the nineteenth annual adminis- 

 trative report of the president, together with the 

 reports on investigations and projects submitted by 

 the various departments of the institution. Two sec- 

 tions of the presidential address, the financial records 

 and the list of the institution's publications for the 

 year, disclose some interesting facts. The total income 

 available for the year ending October 31, 1920, was 

 roughly 388,000?., and of this sum about 278,000?. 

 was allotted to the various departments. The Depart- 

 ment of Terrestrial Magnetism received the biggest 



grant, some 51,000?., while Mount Wilson Observa- 

 tory received 45,000?., and the Geophysical Labora- 

 tory the notable sum of 31,000?. Another large item 

 in the expenditure was the production of the well- 

 known publications of the Carnegie Institution, of 

 which twenty-two were issued and a further eight 

 authorised for publication during the course of the year ; 

 this work absorbed some 17,000?. The bulk of the 

 Year Book is devoted to reports showing the progress 

 of investigations carried on during the year; reports 

 of directors of departments are given first, followed 

 by reports of recipients of grants for other investiga- 

 tions, the latter being arranged according to subject. 



The latest catalogue (No. 415) of second-hand books 

 offered for sale by Mr. F. Edwards, 83 High Street, 

 Marylebone, W. i, deals with works relating to British 

 and foreign birds, and natural history voyages and 

 travels. It contains nearly 400 items, many formerly 

 the property of the late Dr. F. du Cane Godman, and 

 several choice and scarce works. It will appeal to 

 ornithologists. The catalogue is to be obtained upon 

 application. 



Our Astronomical Column. 



Dr. Hill's Cusped Orbit. — Dr. Hill in his " Re- 

 searches on the Lunar Theory " described a certain 

 case of satellite motion in which the orbit of the 

 satellite relatively to the primary was cusped at first 

 and last quarter. The period of such a satellite in 

 the earth's case would be 205 days. Dr. Hill supposed 

 that this was the orbit of maximum lunation, but M. 

 Henri Poincar^ later showed that still larger orbits 

 were possible, with loops replacing the cusps. 



Astr. Nach. No. 5101 contains a paper by Prof. 

 T. J. J. See quoting results of the late Dr. John N. 

 Stockwell, in which the latter claimed to have shown 

 that Dr. Hill's cusped orbit was erroneous and should 

 be replaced by a flattened oval with a period of luna- 

 tion of 2475 days. He further asserted that Jacobi's 

 integral (used by Dr. Hill) was based on incorrect 

 mechanical principles. Both Prof. See and Dr. 

 Stockwell appear to have overlooked a paper by 

 R. Moritz in Mon. Not. R.A.S. for November, 1917, 

 in which the latter re-investigated the cusped orbit 

 of Dr. Hill by the method of mechanical quadratures 

 used by Dr. P. H. Co well for the eighth satellite 

 of Jupiter and for Halley's comet. Needless to say, 

 this method is independent of Jacobi's integral, 

 and involves nothing beyond the elementary prin- 

 ciples of accelerated motion. The result has led to 

 the detection of a few unimportant numerical errors 

 in Dr. Hill's work, but the accuracy of the cusped 

 orbit is substantially verified. If Dr. Hill's figures 

 had been rigorously exact, the minimum distance 

 of the satellite from the earth would have been 

 attained when the angle of motion relatively to 

 the sun was exactly 90° from the cusp. The actual 

 figures given by the quadrature method are 90° 6' 51'. 

 The error is mainly due to the small errata in Dr. 

 Hill's work, though a little may be ascribed to the 

 inevitable cumulative error of mechanical quadratures. 

 It would therefore appear that Dr. Stockwell 's 

 method must involve some fallacy, since the orbit 

 that he gives for a period of 2o8| days is of quite a 

 different shape from the cusped orbit, and differs 

 little from an ellipse. 



NO. 2694, VOL. 107] 



SrONYHLRST COLLEGE OBSERVATORY. — We have 



received the annual report of this observatory from 

 the director, the Rev, A. L. Cortie, S.J. The regular 

 observation of the sun has been continued, and the 

 results show a steady decline in spot-activity; the disc 

 being without spots on four days in September last 

 for the first time since 1916. The director com- 

 municated a paper to the British Association at Cardiff 

 on the connection between faculae and calcium flocculi, 

 showing that the correlation of the two is so close 

 that the faculae are probably the bases of the flocculi. 



It will be remembered that on a former occasion 

 Father Cortie dwelt on the importance of the latitude 

 of sun-spots as an index of their magnetic effect on 

 the earth. This was borne out by the spot of last 

 month, which, although not at all abnormal in its 

 extent, passed very near the centre of the disc, 

 producing great magnetic disturbance and extremely 

 bright aurorae. 



The report contains an obituary notice of Bro. W. 

 McKeon, S.J., who died on May 18, 1920. He was 

 on the observatory staff for forty-two years, the 

 majority of the drawings of spots made at the observa- 

 tory being his work. 



" L'ASTRONOMIE ET LES ASTRONOMES." — M. AugUSte 



Collard, librarian of the Royal Observatory of 

 Belgium, has published a useful bibliography under 

 this title, which forms a brochure of 119 pages. 

 It is divided under the headings : (i) Dictionaries and ) 

 Encyclopaedias of Astronomy; (2) Biographies of 

 Astronomers; (3) Treatises on Astronomy, subdivided 

 into many sections ; (4) Histories ; (5) Bibliographies ; 

 (6) Atlases ; (7) Reviews ; and (8) Tables. 



The works under the various headings are not 

 arranged in alphabetical order, but there are alpha- 

 betical indices at the end. There are also in many 

 cases brief notes summarising the scope of the work, 

 which are a useful supplement to the mere statement 

 of the author's name and the title. The book promises 

 to be useful ; it is one of a series of similar works of 

 reference published by G. Van Oest et Cie, National 

 Library of Art and History, Brussels. 



