RADIANT HEAT AND ITS RELATIONS. 89 



to the visible, rays. In the case of the radiation from 

 our fire, about 98 per cent, of the whole emission con 

 sists of invisible rays ; the body, therefore, which was 

 most opaque to these triumphed as an absorber, though 

 that body was a white one. 



And here it is worth while to consider the manner 

 in which we obtain from natural facts what may be 

 called their intellectual value. Throughout the pro- 

 cesses of Nature we have interdependence and harmony ; 

 and the main value of physics, considered as a mental 

 discipline, consists in the tracing out of this inter- 

 dependence, and the demonstration of this harmony. 

 The outward and visible phenomena are the counters 

 of the intellect ; and our science would not be worthy 

 of its name and fame if it halted at facts, however 

 practically useful, and neglected the laws which accom- 

 pany and rule the phenomena. Let us endeavour, 

 then, to extract from the experiment of Franklin all 

 that it can yield, calling to our aid the knowledge 

 which our predecessors have already stored. Let us 

 imagine two pieces of cloth of the same texture, the 

 one black and the other white, placed upon sunned 

 snow. Fixing our attention on the white piece, let us 

 enquire whether there is any reason to expect that it 

 will sink in the snow at all. There is knowledge at 

 hand which enables us to reply at once in the negative. 

 There is, on the contrary, reason to expect that, after a 

 sufficient exposure, the bit of cloth will be found on an 

 eminence instead of in a hollow ; that instead of a 

 depression, we shall have a relative elevation of the 

 bit of cloth. For, as regards the luminous rays of the 

 sun, the cloth and the snow are alike powerless ; the 

 one cannot be warmed, nor the other melted, by such 

 rays. The cloth is white and the snow is white, because 

 their confusedly mingled fibres and particles are incom- 



