10 NATURAL THEOLOGY. 



seem to be a force sufficient to shatter to atoms 

 the hardest bodies. 



How then is this effect, the consequence of 

 such prodigious velocity, guarded against? By a 

 proportionable minuteness of the particles of which 

 light is composed. It is impossible for the human 

 mind to imagine to itself any thing so small as a 

 particle of light. But tliis extreme exility, though 

 difficult to conceive, it is easy to prove. A drop 

 of tallow, expended in the wick of a farthing can- 

 dle, shall send forth rays sufficient to fill a hemis- 

 phere of a mile diameter ; and to fill it so full of 

 these rays, that an aperture not larger than the 

 pupil of an eye, w^herever it be placed within the 

 hemisphere, shall be sure to receive some of them. 

 What floods of light are continually poured from 

 the sun, we cannot estimate ; but the immensity of 

 the sphere which is filled with particles, even if it 

 reached no further than the orbit of the earth, we 

 can in some sort compute ; and we have reason to 

 believe, that, throughout this whole region, the 

 particles of light lie, in latitude at least, near to 

 one another. The spissitude of the sun's rays at 

 the earth is such, that the number which falls upon 

 a burning-glass of an inch diameter, is sufficient, 

 when concentrated, to set wood on fire. 



The tenuity and the velocity of particles of light, 

 as ascertained by separate observations may be 

 said to be proportioned to each other, both surpass- 

 ing our utmost stretch of comprehension ; but pro- 

 portioned. And it is this proportion alone which 



