208 THE CHEMISTRY OF THE SUN. [CHAP. xv. 



What did we want ? We wanted to settle those questions of 

 the variations of spectra seen in our laboratories, and the 

 variations observed when we passed from the spectrum, say of 

 iron, on the earth, to the spectrum of iron in solar spots and 

 storms. 



The coincidence with Fraunhofer lines, of lines of different 

 substances seen in our laboratories which had been referred to by 

 Angstrom and KirchhofP, also required investigation. What 

 more ready means of doing this what more perfect means 

 were there than those placed at our disposal by photography ? 

 Photography has no personal equation, it has no inducement to 

 twist a result either in one direction or the other, and it more- 

 over has this excellent thing about it, that the results can be 

 multiplied a thousandfold and can be recorded in an absolutely 

 easy and safe manner. There were other reasons why photo- 

 graphy should be introduced in this part of the work. We see 

 at once that it was quite easy to introduce the process of puri- 

 fication of the spectra to which I have already drawn attention, 

 by merely comparing a series of photographs. Again, it was 

 quite possible by the use of the electric lamp to very consider- 

 ably surpass the dispersion which Angstrom had employed. So 

 that, if impurities had been suggested, there was now a method 

 which has not yet been challenged of getting rid of them ; if 

 the dispersion was then insufficient there was nothing to pre- 

 vent it being made very much more considerable, because a 

 perfect photograph will bear a very considerable amount of 

 magnification. 



There were also many other obvious lines of research, especi- 

 ally some in connection with multiple spectra, which seemed to 

 promise new facts. But the upshot of the whole matter was 

 that more work was wanted, and that in this work photography 

 should be utilized. 



