

SOLAR PHOTOGRAPHY. 



47 



was wrong. We have, however, not yet finished 

 with the paper. At the close of it he refers to 

 a matter which is of considerable interest, show- 

 ing, as it does, how near one may be to a most 

 important discovery and yet miss it. I give it 

 in the Professor's own words : 



" Had the weather proved unfavourable for view- 

 ing the eclipse, I intended to have tried the experi- 

 ment by forming an image of the sun by using 

 lens of long focus, stopping alternately by means 

 of a screen the exterior and central moiety of his 

 rays; and restoring the remainder to parallelism by 

 means of a second lens, then suffering these to 

 fall upon a slit as before. The result of my ex- 

 periment during the eclipse seemed, however, so 

 decisive as to no marked change being produced at 

 the sun's edges that I have thought it unnecessary ^. 

 to repeat it." 



It will be seen that Forbes all but introduced 

 the method of localisation of solar phenomena, 

 which is brought about by throwing an image 

 of the sun on the slit-plate of the spectroscope, 

 whereby we are enabled to examine the spectrum 

 of any particular part of disc or limb at pleasure. 

 Yet, although Forbes came so near applying this 

 principle, which has turned out of so high im- 

 portance, we had to wait until 1866 before it 

 was actually carried out. 



The year 1842 marked another very great 

 advance in our knowledge of the solar spectrum. 

 While experimenting with photography, l Bec- 

 querel obtained by its means a representation of 

 the whole spectrum with nearly all the lines 



1 Bibliotheque Vniverselle de Geneve, t. 39-40, p. 341 (1842). 



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