Ixv 



solid form, the substance then assumes the liquid state. If the motions 

 of the particles be still more highly agitated the fluid will assume the 

 gaseous form. 



This vibratory motion is simply so much force imparted by the hotter 

 body to the ether, the air, or other cooler body in contact with it, and, un- 

 less the excessive motion in the warmer body be kept up by some other 

 force, its vibrations gradually subside to that condition which corresponds 

 with the temperature of the adjacentor surroundingbodies. When itfaUs 

 below that, from any cause, the vibratory rrotion of its parMcleswill re- 

 ceive additional motion from 'he vibratory atoms of the adjacent onep. 



That molecular motion or heat is simply a form oi force, may be 

 proved by causing the warmth in the hand to be converted into mechan- 

 ical effector visible motion. 



For instance, if the hand be held near the bulb of a thermometer, the 

 force or heat radiating from it will cause the mercury to rise. Or this 

 force, stored in the hand as heat, may be converted into another form of 

 force, and this still into another kind, and this latter form, being equally 

 invisible, may be made to produce a visible mechanical effect. Thus, if 

 the hand be held near a thermoelectric pile, the heat discharged by the 

 hand will be converted into electricity, this will in turn induce still another 

 form of force, magnetism, and this will cause the needle connected with 

 the pile to be deflected, and so produce visible dynamic force, or motion. 



To our countryman, Benjamin Thompson, better known as Count 

 Rumford, belongs the credit of first proving that heat is simply molecular 

 motion. This he did by boiling water with the heat developed by the 

 friction of a blunt or dull drill, made to revolve by horse-power in a brass 

 cannon which he was boring out, the cannon and drill being immersed 

 in a vessel containing the water. Finding that he could continue to 

 create the heat as long as he kept up the friction of the drill, and that 

 neither the drill nor the brass was consumed in the operation, he rightly 

 assumed that •' anything which any insulated body or system of bodies 

 can continue to furnish without limitation, cannot possibly be a material 

 substance." Thus the theory of caloric, as taught in the early part of 

 this century, was overthrown. Heat, or, as it was then termed, caloric, 

 was supposed to be a highly attenuated, mobile and imponderable fluid 

 contained within other matter, or attracted by other matter, and capable 

 of being extracted or given off by such matter, just as moisture is ab- 

 sorbed by, or evaporated from, a piece of sand-stone. 



The friction of Rumford's drill excited in a high degree the molecular 

 motion of the two metals, and this motion was manifested as heat, and 

 by it the water was boiled. The force developed by the horse might at 

 first be deemed the primary one which produced the heat in the cannon, 

 but a little reflection would lead us to see that quite as much water could 

 be boiled by the direct combustion of the provender consumed by the horse 

 during his labor, if this food had been judiciously burned under the water. 

 We must therefore consider the sun as the prime motor, for the provender 

 was simply the result of the energy of the sun's rays, by which the con- 



