EMANATIONS OF LIGHT. 27 



coming from the nearest point would be strongest. Thus 

 the radiances issuing from the two centres would encounter 

 each other, in the space common to both, at every possible 

 angle and with every possible disparity of force. 



And yet, so far as we can discover, such rays do not in- 

 terfere with each other in the least ; for, wherever you put 

 your eye within the portion traversed by the light from 

 both the centres, if you turn your eye to either, you have 

 its image as clearly and distinctly painted on your retina 

 as if the other did not exist ; that is to say, the radiance 

 which comes from one of the points, though its track has 

 been crossed all the way by the emanation from the other 

 both filling the space completely is not disturbed or in- 

 terfered with by the other in the slightest degree. 



This is wonderful, and it is for the purpose of furnishing 

 a clear, simple, and precise idea of the nature of this mys- 

 tery, as the foundation of a right understanding of what 

 is to follow, that I have made these suppositions of candles 

 in the air. 



If you have followed what I have said closely enough to 

 have received distinctly an idea of the nature of this won- 

 der of the non-interference, in the ordinary sense, of lumin- 

 ous emanations moving in contrary directions, and cross- 

 ing each other at every possible angle and on the same 

 track, you are prepared to appreciate in some degree the 

 amazing magnitude and extent of it. Every star in the 

 sky is the centre of a sphere that is illuminated by its ra- 

 diation in the manner I have explained a sphere, too, 

 which is so enormous in extent that its magnitude and 

 grandeur surpass all human conception. 



Light is proved to move at the rate of between one and 

 two hundred thousand miles in a second, which is sufficient 

 to carry it round the earth in the seventh part of a second, 

 and there are stars so remote that it would require Hun- 



