Scientific Lectures. 121 



SCIENTIFIC LECTURES 



BEFORE THE 



AMERICAN INSTITUTE OF THE CITY OF NEW YORK, 



ACADEMY OF MUSIC, FOURTEENTH STREET AND IRVING PLACE. 



I. THE NATURE AND SOURCES OF LIGHT. 



Delivered November 23d, 1871. 



By Henry Morton, Ph.D., President op the Stevens Institute op Technology. 



I think I shall not surprise any one who now hears me by saying 

 that light is not a substance, but a force — not a kind of matter, but 

 a quality of motion affecting matter. That the sun is not a vast 

 fortress forever bombarding us with an infinite rain of projectiles, 

 but a huge bell-tower, eternally surging out grand symphonies of 

 light and color in harmonious waves. 



But one of the many evidences of this fact it may not be amiss to 

 mention in this connection. By three totally distinct methods the 

 velocity of light has been measured, and shown to be about 200,000 

 miles in a second, or about 6,000 times as great as the initial velocity 

 of a cannon ball. Now, we know that the destructive action of a 

 projectile varies with its mass or weight, and the square of its 

 velocity ; hence, if light were a substance as heavy as iron, its destruc- 

 tive effect on striking us or any object would be 36,000,000 times as 

 great as that of a cannon ball, or, assuming that it was 1,000 times 

 lighter than hydrogen gas, which is the lightest substance we know 

 about, its blows would still do more than 2,000 times the damage of 

 the fiercest cannonade which ever assailed a beleaguered fortress, or 

 mowed down the advancing columns of an army. 



And yet the leaf that trembles in the gentlest breeze spreads its 



