OF COMMON MATTER. 159 



above opinion, I shall merely quote a passage 

 from Dr. THOMSON'S valuable System of 

 Chemistry. " A 29lb. ball, if thrown from the 

 hand, makes no impression upon a common 

 wall, but when discharged from a cannon with 

 the velocity of 1300 feet in a second of time, it 

 will then be found to shatter the wall to pieces: 

 the greater velocity, therefore, with which a 

 body moves, the greater the effect which it is 

 capable of producing; consequently, to pro- 

 duce any effect whatever, by a body however 

 small, we have only to increase its velocity 

 sufficiently; and, in order to prevent a body 

 from producing a given effect, its quantity must 

 be diminished, in proportion as its velocity is 

 decreased : now the velocity of light is so great, 

 that if each of its particles weighed the 1000 

 part of a grain of sand, its force would be 

 greater than that of a bullet, discharged from a 

 musket; were it even the millionth part of a 

 grain in weight, it would destroy every thing 

 against which it struck : if it even weighed the 

 millionth part of that, it would still have a very 

 sensible force; but how much less must be 

 the weight of a particle of light, which makes 

 no sensible impression upon so delicate an or- 

 gan as the eye? We are certain then, that no 

 particle of light, is 1,000,000,000,000th of a 

 grain ; but were we even to suppose it of that 

 size, the addition of 900 millions of particles 



