448 THE MODERN THEOKY OF LIGHT. 



energy were properly directed, produce quite as much real light as is 

 produced by all this mass of mechanism and consumption of material. 

 There might perhaps be something contrary to the laws of nature in 

 thus hoping to get and utilize some specific kind of radiation without 

 the rest, but Lord Eayleigh has shown in a short communication to the 

 British Association at York that it is not so, and that therefore we have 

 a right to try to do it. 



We do not yet know how, it is true, but it is one of the things we have 

 got to learn. 



Any one looking at a common glow-worm must be struck with the 

 fact that not by ordinary combustion, nor yet on the steam-engine and 

 dynamo principle, is that easy light produced. Very little waste radia- 

 tion is there from phosphorescent things in general. Light of the kind 

 able to afitect the retina is directly emitted ; and for this, for even a 

 large sujiply of this, a modicum of energy suflflces. 



Solar radiation consists of waves of all sizes, it is true ; but then solar 

 radiation has innumerable things to do besides making things visible. 

 The whole of its energy is useful. In artificial lighting nothing but light 

 is desired ; when heat is wanted it is best obtained separately, by com- 

 bustion. And so soon as we clearly recognize that light is an electrical 

 vibration, so soon shall we begin to beat about for some mode of exciting 

 and maintaining an electrical vibration of any required degree of rapidity. 

 When this has been accomplished, the problem ot artificial lighting will 

 have been solved. 



