1 32 LIFE AND EXPERIENCES CHAP. 



light, which was more successful than the former one 

 on the same subject, because I was able to illustrate it 

 by novel and striking experiments as well as to give 

 the results of further investigation. I found that it was 

 possible to seal up in a glass bulb the sensitive mixture 

 of equal volumes of chlorine and hydrogen, and that 

 the mixture contained in these hermetically sealed bulbs 

 could be preserved in the dark for any length of time, 

 and these lent themselves to a large number of striking 

 experiments. One of the best of these consisted in 

 enclosing one of these bulbs in a lantern, one side of 

 which was glazed by a pane of red glass, another by a 

 pane of blue, a third by a pane of yellow, and a fourth 

 by a colourless pane. On firing in front of the red glass 

 a mixture of chlorate of potash and magnesium powder 

 no effect was produced, as the red glass cut off all 

 chemically active rays. This also occurred with the 

 yellow glass, but on firing the mixture in front of the 

 blue glass a loud explosion took place, combination 

 having been brought about by the more refrangible rays. 

 On May 6th, 1864, I gave a lecture describing some 

 recent discoveries by means of spectrum analysis, especi- 

 ally that of indium, and also discussed the application of 

 spectrum analysis to the manufacture of steel. I had 

 investigated this subject at Brown's Atlas Works in 

 Sheffield, with the result that the chemical changes 

 which occurred in the Bessemer process could be accu- 

 rately noted, and the point at which it was necessary 

 to cut off the blast of air was ascertained with a greater 

 precision than was possible with the unassisted eye. On 

 this occasion I also made use, for the first time, of the 

 light of burning magnesium wire for photographic 

 purposes, and photographed Faraday (here reproduced) 

 during the lecture, having also done the same previously 



