TRANSACTIONS OF SECTION A. 665 



diameter with an 8-inch refractor of the Liverpool Ohservatory. In 1852 De la 

 Eue began experimenting in lunar photography. He employed a reflector of some 

 10 feet focal length and about 13 inches diameter. A very complete account of 

 hh methods is given in a paper read before the British Association. Mr. Ruther- 

 furd at a later date having tried an IH-inch refractor, and also a 13-inch reflector, 

 finally constructed a photographic refracting telescope, and produced some of the 

 finest pictures of the moon that were ever taken until recent years. Also Henry 

 Draper's picture of the moon taken September 3, 1863, remained unsurpassed for 

 a quarter of a century. 



Admirable photographs of the lunar surface have been published in recent years 

 by the Lick Olaservatory and others. T myself devoted considerable attention to 

 this subject at one time. Photographs surpassing anything before attempted were 

 published in 1896-99 by MM. Loewy and Puiseux, taken with the Equatorial 

 Coude of the Paris Observatory. 



Star prints were first secured at Harvard College, under the direction of W. 0. 

 Bond, in 1850 ; and his son, G. P. Bond, made in 1857 a most promising start with 

 double-star measurements on sensitive plates, his subject being the well-known 

 pair in the tail of the Great Bear. The competence of the photographic method to 

 meet the stringent requirements of exact astronomy was still more decisively 

 shown in 1866 by Dr. Gould's determination from his plates of nearly fifty stars 

 in the Pleiades. Their comparison with Bessel's places for tlie same objects 

 proved that the lapse of a score of years had made no difl'erence in the configura- 

 • tion of tliat immemorial cluster ; and Professor Jacoby's recent measures of 

 Eutherfurd's photographs taken in 1872 and 1874 enforce the same conclusion. 



The above facts are so forcible that no wonder that at the Astrophotographic 

 Congress held in Paris in 1887 it was decided to make a photographic survey of 

 the heavens, and now eighteen photographic telescopes of 13 inches aperture are in 

 operation in various parts of world, for the purpose of preparing the international 

 astrographic chart, and it was hoped that the catalogue plates would be completed 

 by 1900. 



Photography has been applied so assiduously to the discovery of minor planets 

 that something like 450 are now known, the most noteworthy, perhaps, as 

 regards utility being the discovery of Eros (433) in 1898 by Herr "Witt at the 

 Observatory Urania, near Berlin. 



AVith regard to the application of photography to recording the form of various 

 nebulae, it is interesting to quote a passage from Dick's 'Practical Astronomer,' 

 published in 1845, as opposed to Herschel's opinion that the photography of a 

 nebula would never be impossible. 



' It might, perhaps, be considered as beyond the bounds of probability to expect 

 that even the distant nebulas might thus be fixed, and a delineation of their objects 

 produced, which shall be capable of being magnified by microscopes. But we 

 ought to consider that the art is only in its infancy, and that plates of a more 

 delicate nature than those hitherto used may yet be prepared, and that other 

 properties of light may yet be discovered, which shall facilitate such designs. For 

 we ought now to set no boundaries to the discoveries of science, and to the 

 practical applications of scientific discovery, which genius and art may accomplish.' 



It was not, however, until 1880 that Draper first photographed the Orion 

 Nebula, and later by three years I succeeded in doing the same thing with an 

 exposure of only thirty-seven minutes. In December 1885 the brothers Henry by 

 the aid of photography found that the Pleiades were involved in a nebula, part of 

 which, however, had been seen by myself ' with my 3-foot reflector in February 

 1880, and later, February 1886, it was also partly discerned at Pulkowa with 

 the 30-inch refractor then newly erected. 



Still more nebulosity was shown b\ Dr. Eoberts's photograph s,'-' taken with his 

 20-inch reflector in October and December 1886, when the whole western side of the 

 group was shown to be involved in a vast nebula, whilst a later photograph taken 

 by MM. Henry early in 1888 showed that practically the whole of the group was 

 a shoal of nebulous matter. 



' Monthly Kotice$, vpl, xl. p. 376. ' Monthly Notices, vol, xlyii. p, ?4. 



