NEW CHEMICAL REACTIONS. 71 
other a dweller in England,* who never in their inquiries 
consciously set a practical object before them whose only 
stimulus was the fascination which draws the climber to a 
never-trodden peak, and would have made Csesar quit his 
victories for the sources of the Nile. That the knowl- 
edge brought to us by those prophets, priests, and kings 
of science is what the world calls " useful knowledge," the 
triumphant application of their discoveries proves. But 
science has another function to fulfill, in the storing and 
the training of the human mind; and I would base my 
appeal to you on the specimen which has this evening been 
brought before you, whether any system of education at 
the present day 'can be deemed even approximately com- 
plete, in which the knowledge of Nature is neglected or 
ignored. 
CHAPTER IV. 
NEW CHEMICAL REACTIONS PRODUCED BY LIGHT. 
1868-69. 
MEASURED by their power, not to excite vision, but to 
produce heat in other words, measured by their absolute 
energy the ultra-red waves of the sun and of the electric 
light, as shown in the preceding articles, far transcend the 
visible. In the domain of chemistry, however, there are 
numerous cases in which the more powerful waves are 
ineffectual; while the more minute waves, through what 
may be called their timeliness of application, are able to 
produce great effects. A series of these, of a novel and 
beautiful character, discovered in 1868, and further illus- 
trated in subsequent years, may be exhibited by subjecting 
the vapors of volatile liquids to the action of concentrated 
sunlight, or to the concentrated beam of the electric light. 
Their investigation led up to the discourse on "Dust and 
Disease" which follows in this volume ; and for this reason 
some account of them is introduced here. 
* Faraday. 
