NEW CONCEPTIONS IN SCIENCE 



strain or whirl even the vortex-ring imagined long 

 ago by Lord Kelvin. 



Here available evidence stops and fancy may 

 have freest rein. So, if we like, we may imagine 

 light to be just what old Sir Isaac imagined it long 

 ago just a bombardment of the retina by a hail of 

 flying corpuscles, given off by every incandescent 

 body. If this be a little difficult of belief, seeing 

 how sensitive is the active part of the eye, we may 

 reflect that the corpuscle is amazingly small. We 

 lack appropriate units of measurement, for to com- 

 pute them in fractions of an inch would be like 

 measuring the thickness of a hair, say, in fractions 

 of a mile. Lord Kelvin figures out an average 

 atom at less than one twenty-five-millionth of an 

 inch in diameter. A corpuscle is certainly not 

 more than a tenth part of that, and it may be a 

 great deal smaller. 



The subject is a little complex, and mayhap a 

 trifle heavy. So I have preferred to retain this 

 slight sketch as a sort of introduction to a more 

 detailed account in the next chapter. 



