596 



SCIENCE. 



[N. S. Vol. XII. No. 303. 



a 13-incli reflector, finally constructed a 

 photographic refracting telescope, and pro- 

 duced 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, re- 

 mained unsurpassed for a quarter of a cen- 

 tury. 



Admirable photographs of the lunar sur- 

 face have been published in recent years by 

 the Lick Observatory and others. I myself 

 devoted considerable attention to this sub- 

 ject at one time ; but only those surpassing 

 anything before attempted have been pub- 

 lished in 1896-99 by MM. Loewy and Pui- 

 seux, taken with the Equatorial Coude of 

 the Paris Observatory. 



Star prints were first secured at Harvard 

 College, under the direction of W. C. 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 the 

 same objects proved that the lapse of 

 & score of years had made no difference 

 in the configuration of that immemorial 

 cluster ; and Professor Jacoby's recent 

 measures of Rutherfurd's photographs taken 

 in 1872 and 1874 enforce the same conclu- 

 sion. 



The above facts are so forcible that no 

 wonder that at the Astrophotographic Con- 

 gress 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 as- 

 trographic chart, and it was hoped that the 



catalogue plates would be completed by 

 1900. 



Photography has been applied so assid- 

 uously 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 of 

 Urania, near Berlin. 



With regard to the application of photog- 

 raphy to recording the form of various 

 nebulte, it is interesting to quote a passage 

 from Dick's ' Practical Astronomer,' pub- 

 lished in 1845, as opposed to Herschel's 

 opinion that the photography of a nebula 

 would never be possible. 



" It might, perhaps, be considered as be- 

 yond the bounds of probability to expect 

 that even the distant nebulae 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 in- 

 fancy, 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 Ne- 

 bula, and later by three years I succeeded 

 in doing the same thing with an exposure 

 of only thirty-seven minutes. In Decem- 

 ber, 1885, the brothers Henry by the aid 

 of photography found that the Pleiades were 

 involved in a nebula, part of which, how- 

 ever, 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 reflector then 

 newly erected. 



* Monthly Notices, Vol. XL., p. 376. 



