September 16, 1898.] 



SCIENCE, 



353 



lae with this object, and succeeded, with 

 51 minutes' exposure, using the dry plate, 

 in getting a good picture of the brighter 

 portions of the nebula. This was the first 

 nebular photograph. With 104 minutes' 

 exposure in March, 1881, with an 11-inch 

 refractor, he secured a still better plate, 

 which showed stars down to the 14.7 mag- 

 nitude, which were visually beyond the 

 reach of the same telescope. But in March, 

 1882, he obtained the best picture of this 

 wonderful nebula, with an exposure of 137 

 minutes. These pictures marked a new 

 era in the study of the nebulse. AVhen 

 these results were communicated to the 

 French Academy by Dr. Draper, Janssen 

 took up the subject with a silver-on-glass 

 mirror of very short focus, having the ex- 

 traordinary ratio of aperture to focus of J; 

 the aperture being 20 inches, with a focus 

 of 63 inches. This remarkable instrument 

 was constructed in 1870 for the total solar 

 eclipse of 1871. With this Janssen found 

 it easy to photograph the brightest parts of 

 the nebula with comparatively short expo- 

 sures. This extremely powerful photo- 

 graphic instrument seems to have been 

 unused for the past fifteen years ; but very 

 recently it has been brought into use again, 

 I understand, with the most astonishing 

 results in photographing the nebulae. Un- 

 fortunately for science, the death of Dr. 

 Draper, in 1882, put a stop in America to the 

 work he had inaugurated. But it was at 

 once taken up in England by Common, who, 

 with a three-foot reflector, attained rapid 

 and immediate success. His photographs 

 of the great nebula of Orion are still classic. 

 They were a great advance over the work 

 of Draper, for the reflector was not only a 

 larger telescope, but was also better adapted 

 for photographic purposes, and especially 

 for photographing the nebulse. In January 

 of 1883, with only 37 minutes' exposure, he 

 secured what was by far the most striking 

 and beautiful picture which had yet been 



taken of the great nebula. These pictures 

 greatly extended the region of nebulosity, 

 and the delicate details were also better 

 shown. 



The writer remembers how much he was 

 impressed a few years later with the beauty 

 of one of Common's photographs. It cre- 

 ated in him the first ambition to do work of 

 this kind. Indeed, this picture, and one of 

 a densely crowded region of a part of the 

 constellation of Cygnus, by the Henry 

 Brothers, first called his attention to the 

 great value of the photographic plate for 

 astronomical purposes. It was at this time 

 that the writer conceived the idea of pho- 

 tographing the Milky Way, though the ex- 

 periments were not then successful for the 

 want of a proper instrument. The great 

 nebula, which has always had such a fas- 

 cination for astronomers, was subsequently 

 taken up by Isaac Eoberts, who, by very 

 prolonged exposures, still further extended 

 the nebulous region and secured very 

 beautiful pictures of it. Among the fin- 

 est photographs of this object that have 

 been made in recent years is one taken 

 by Dr. H. C. Wilson at Northfield, Minn., 

 with an 8-inch photographic refractor with 

 an exposure of nine hours. The amount 

 and sharpness of detail shown on this 

 beautiful photograph is very striking, and 

 essentially embraces all that has been done 

 on this nebula by photography up to the 

 present time. 



E. E. Barnard. 



Yeekes Obseevaioky. 



( To be concluded. ) 



TEE INTERNATIONAL CONGRESS OF ZO- 

 OLOGY* 

 The Fourth International Congress of 

 Zoology met at Cambridge on Tuesday, 

 August 23d, and the four following days. 

 There were about 300 members present. 

 The attendance from America was scarcely 

 * Based on reports in the London Times. 



