PROGEESS OP ASTRONOMICAL PHOTOGRAPHY. 195 



previously existed, and which I have had the exquisite pleasure of 

 J3eholding in his observatory at Cranford. 



" Man looks aloft, and, with erected eyes, 

 Beholds his own hereditary skies." 



I must now turn to a department in celestial photography, where 

 Mr. De La Rue stands almost alone. I speak of heliograpliy. In 

 April, 1854. Sir John Plerschel, in a letter to Colonel Sabine, recom- 

 mended that daily photographic records of the sun should be obtained 

 at some observatory. Accordingly the Royal Society placed at the 

 disposal of the Kew committee a sum of money to promote that ob- 

 ject, and Mr. De La Rue was requested to administer the grant. 



It becomes necessary to mention that Arago, in his elegant and 

 popular work on astronomy, translated by two eminent fellows of our 

 society, states that MM. Fizeau and Foucault, in 1845, obtained a 

 photographic image of the sun, and two spots on its disk, delineated 

 with much apparent sharpness and accuracy; but, however this may 

 be,'^' it is certain that no uniformly successful method of taking images 

 of the sun had been devised until Mr. De La Rue took up the problem 

 for investigation. 



Yet great as had been the difficulties in obtaining a really accurate 

 and available picture of the moon they sink into insignificance when 

 compared with those which had to be overcome in the photography 

 of the sun; for to obtain any automatic pictures of the sun's photo- 

 sphere available for practical purposes it was found necessary to in- 

 stitute a series of preliminary experiments before actual operations 

 could be successfully commenced. At first nothing but burnt up and 

 solarized pictures could be obtained by any method that had hitherto 

 been devised, or with any the least sensitive of the media that could 

 be procured. Now, with the help of the Kew photoheliogj-aph, as 

 devised by him, and described in vol. xv of the Monthly Notices, 

 heliography is the easiest and simplest kind of astronomical photo- 

 graphy. The method devised by Mr. De La Rue will enable any pho- 

 tographer of common average skill to take excellent heliographs. 

 Professor Selwyn, of Cambridge, succeeds in getting good pictures 

 of the sun with the apparatus made for him by Mr. Dalmeyer, after 

 the pattern of the Kew photoheliograph. 



Mr. De La Rue announced at the last meeting of the society that 

 by applying the stereoscope to the examination of the sun's disk, as 

 he had formerly done in the case of the moon, he had discovered 

 that the faculas on the surface of the sun are to be found in the outer 

 or highest regions of the solar photosphere. 



I ought not to conclude without alluding to Mr. De La Rue's obser- 

 vations on the solar eclipse of 1860; but it must not be forgotten 

 that one daguerreotype picture was taken by Dr. Busch of the solar 



'■- Hespecting this photography of tlie sun, the index of the Comptes Rendus has heen 

 searched all through, under the heads of Arago, Photography, Soleil, Faeau, Foucault, Daguer- 

 reotype, and Faye, and no mention has heen found whatever of the sun's picture in 18i5 ; 

 and there has not been found any reference to it, excepting the plate in the body of the 

 ..original work itself. 



