SOURCES OF HEAT AND COLD. 

 The galvanophorus, or galvanic substitute for the electrophones 



" The preceding figure represents an instrument for igniting a. 

 lamp, by means of a galvanic discharge, from a calorimotor." 



" The plunger, P, being depressed, by means of the handle at- 

 tached to it, some acid, contained in the box, B, is displaced, so as 

 to rise among the galvanic plates. By the consequent evolution of 

 the galvanic fluid, a platina wire (fastened between the brass rods 

 forming the poles of the calorimotor, and projecting over the lamp, as 

 seen at R,) is rendered white hot, and a filament of the wick, pre- 

 viously laid upon it, is inflamed." 



" The weight, W, acts as a counterpoise to the plunger, and keeps 

 it out of the acid, when it is not depressed by the hand." 



(e.) Condensation of aeriform bodies by pressure and cold. 

 This topic is already anticipated under specific heat and vapors. 

 Vapors and gas mechanically condensed, as by the syringe and piston, 

 give out heat ; vapors impart heat to colder bodies, as in the distill- 

 ing apparatus with its condenser, already mentioned. Compressed 

 oxygen and chlorine give out light, and these gases are said to be 

 the only simple ones that become luminous by pressure. 



(/.) Condensation of solids by mechanical action including fric- 

 tion and percussion. The flint and steel in collision, or two quartz 

 stones struck forcibly together ; any hard stone firmly held upon a 

 revolving grit stone ; the vigorous rubbing together of two sticks ; the 

 friction of branches of trees in stormy weather ; of axles in carts and 

 wagons and of various pnrts of powerful machinery ; of the axles in 



