Foundations of the Universe 281 



of the problems of science, and one of profound practical interest. 

 If we could produce light without heat our "gas bill" would 

 shrink amazingly. So much energy is wasted in the production 

 of heat-waves and ultra-violet waves which we do not want, that 

 90 per cent, or more of the power used in illumination is wasted. 

 Would that the glow-worm, or even the dead herring, would 

 yield us its secret! Phosphorus is the one thing we know as yet 

 that suits the purpose, and it smells! Indeed, our artificial 

 light is not only extravagant in cost, but often poor in colour. 

 The unwary person often buys a garment by artificial light, and 

 is disgusted next morning to find in it a colour which is not 

 wanted. The colour disclosed by the sun was not in the waves 

 of the artificial light. 



Beyond the waves of violet light are the still shorter and 

 more rapid waves the "ultra-violet" waves which are precious 

 to the photographer. As every amateur knows, his plate may 

 safely be exposed to light that comes through a red or an orange 

 screen. Such a screen means "no thoroughfare" for the blue 

 and "beyond-blue" waves, and it is these which arrange the little 

 grains of silver on the plate. It is the same waves which supply 

 the energy to the little green grains of matter (chlorophyll) in 

 the plant, preparing our food and timber for us, as will be seen 

 later. The tree struggles upward and spreads out its leaves 

 fanwise to the blue sky to receive them. In our coal-measures, 

 the mighty dead forests of long ago, are vast stores of sunlight 

 which we are prodigally using up. 



The X-rays are the extreme end, the highest octave, of the 

 series of waves. Their power of penetration implies that they 

 are excessively minute, but even these have not held their secret 

 from the modern physicist. From a series of beautiful experi- 

 ments, in which they were made to pass amongst the atoms of a 

 crystal, we learned their length. It is about the ten-millionth of 

 a millimetre, and a millimetre is about the *V of an inch! 



One of the most recent discoveries, made during a recent 



