Experimental Philosophy. [Lecture 10. 



over by light in a second to agree with what we 

 have just stated. This discovery we owe to 

 Roemer, a Danish astronomer, and it is extremely 

 interesting and important. 



Such, then, is the rapidity with which these rays 

 are darted forward, that the journey they per- 

 form thus in less than eight minutes, a ball from 

 the mouth of a cannon would not complete it 

 in several weeks. But here it may be said, If 

 the velocity of light is so very great, how is it 

 that it does not strike against objects with a mon- 

 strous force? If the finest sand (the objector 

 may continue to observe) was thrown against our 

 bodies with the hundredth part of this velocity, 

 each grain would be as fatal as the stab of a 

 stiletto : How then is it, that we expose, without 

 pain, not only other parts of our bodies to the in- 

 cursions of light, but our eyes, which are a part 

 so exquisitely sensible of every impression ? To 

 answer this objection, experiment will inform us, 

 that the minuteness of the parts of light is still 

 several degrees beyond their velocity ; and they 

 are therefore harmless, because so very small. 

 A ray of light is nothing more than a constant 

 stream of minute parts still flowing from the 

 luminary, so inconceivably little, that a candle, 

 in a single second of time, has been said to dif- 

 fuse several millions of particles of light. The 

 sun furnishes them, and the stars also, without 

 appearing in the least to consume by granting us 

 the supply. Musk, while it diffuses its odour. 



