14 THE FORMS OF WATER IN 



thu heat-waves issuing from non-luminous hot bodies, 

 are frequently called obscure or invisible heat. 



We have here an example of the manner in which 

 phenomena, apparently remote, are connected together 

 in this wonderful system of things that we call Nature. 

 You cannot study a snow-flake profoundly without being 

 led back by it step by step to the constitution of the sun. 

 It is thus throughout Nature. All its parts are inter- 

 dependent, and the study of any one part completely 

 would really involve the study of all. 



§ 5. Experiments to prove the foregoing Statements. 



38. Heat issuing from any source not visibly red 

 cannot be concentrated so as to produce the intense 

 effects just referred to. To produce these it is neces- 

 sary to employ the obscure heat of a body raised to the 

 highest possible state of incandescence. The sun is 

 such a body, and its dark heat is therefore suitable 

 for experiments of this nature. 



39. But in the atmosphere of London, and for ex- 

 periments such as ours, the heat-waves emitted by coke 

 raised to intense whiteness by a current of electricity 

 are much more manageable than the sun's waves. 

 The electric light has also the advantage that its dark 

 radiation embraces a larger proportion of the total ra- 

 diation than the dark heat of the sun. In fact, the force 

 or energy, if I may use the term, of the dark waves oi 

 the electric light is fully seven times that of its light- 



