Art. IX.—Photofjrap/rJc Charting of the Heavens. 

 By R. L. J. Ellery, C.M.G., F.R.S., F.R.A.S. 



Goverumeiit Astrouomer, Melbourue. 



[Read July 9, 1891.] 



The iinmeiise help to astronomy promised by photography, 

 was fully recognised in the earliest days of the practical 

 application of the art, and no sooner had Arago explained to 

 the French Academy of Sciences Daguerre's discoveries in 

 August 1839, than Dr. J. W. Draper, of New York, applied 

 them to astronomical purposes, and the following year 

 presented to the New York Lyceum of Natural Sciences, the 

 first asti-onomical photograpli ever taken, in the shape of a 

 Daguerreotype picture of the moon, which wa*-' one inch in 

 diameter, and requii"ed an exposure of twenty minutes- 

 duration. Dr. Draper and others followed up this early 

 experiment, but the low sensitiveness of the plates then in 

 use, and other difficulties, confined the results to the 

 category of somewhat unsatisfactory experiment for several 

 years. We find some sun pictures were obtained in Paris in 

 1845, and in the same year, pictures of the stars Vega and 

 Castor were secured by Bond of Cambridge, U.S., and of the 

 moon by the same astronomer in 1850. These experiments,, 

 although far from satisfactory, indicated great possibilities, 

 supposing improvements in the art took place. Warren de 

 la Rue, in 1851, made the first substantial advance, which 

 was rendered possible by the discovery of the collodion 

 process. From this time onwards, asti-onomical photography 

 made steady progress, and gave most valuable assistance in 

 the total eclipses since 1854, and on the occasions of the 

 transits of Venus in 1874 and 1882. For the purjwse of 

 recording the apparition, development, and duration of 

 sun spots, photography has given invaluable help, and since 

 1858, pictures of the sun have been obtained every fine day, 

 first in England only, but latterly in many parts of the world. 

 Photographs of the moon, of exquisite delicacy, are now 

 common, and almost a conmiercial commodity. 



