130 Transactions of the American Institute. 



were introduced? I will first answer by an illustration. I here hold 

 in nay hand a tuning-fork, which I make to vibrate violently by draw- 

 ing this piece of wood between its prongs ; but not a sound reaches 

 you. I now rest its handle on this table, and at once it sings out until 

 its voice can be heard in the most distant portion of this large build- 

 ing. Why is this? Largely because the prongs of the fork are too 

 small to take much hold upon the air and set large masses of it in 

 motion ; but when its vibrations are communicated by contact to the 

 entire table, then its whole surface begins, as we may say, to flap up 

 and down, and to fan large areas at once into a responsive motion, 

 which thus is readily brought to your ears. 



So is it with the oxyhydrogen jet. The product of its combustion is 

 too rare to take that hold upon the light-conveying aether which would 

 give it a strong and far-reaching movement, and so we must give it a 

 denser body, either solid, liquid or gaseous, to play the part of the 

 table to the tuning-fork, or to be, as we may say, a sounding-board to 

 its light. 



Next to combustion, as a source of light, comes electricity. Here, 

 again, we have to do with a force about whose nature, proximate or 

 remote, we know nothing. Whether it is a fluid, or two fluids, which 

 produce the various actions we call electric, or whether these are due 

 to a certain motion or a polar arrangement of atoms of matter, we 

 are profoundly ignorant. But we may well believe that, be it what it 

 may, electricity, like other forces, when meeting with resistance, may 

 excite vibratory motions in the resisting body, as the wind does when 

 it whistles through the crack of a window or sounds the strings of an 

 seolean harp ; as the circular saw does when it sings its way through 

 a plank ; as the rain-drops when they patter on a metallic roof, the 

 bullet whistling through the air, or a bar of tin, which " cries " when 

 we bend it in the hand so as to disturb its .polar relation of 

 particles. 



Certain it is that we find, in all cases where electric force is resisted 

 in its motions, that heat, and, where the action is sufficiently strong, 

 light, is developed. Thus, I have here a series of twelve large battery 

 cells, each one of which exposes a zinc surface of about five square 

 feet. I will pass what we call the electric current derived from these 

 through a piece of very thick platinum wire, some eighteen inches 

 long. At once you see it glows with dazzling whiteness, so as actu- 

 ally to light up all the stage. 



Changing the connections, I now have a cup of mercury as one 

 pole of the battery, and a 6teel file as the other. I dip the file in the 





