136 SCIENTIFIC APPARATUS. 



Apparatus for measurement of Latent Heat. [Black, Crawford, 

 Irving, Regnault, &c.] 



(c) CHANGE OF TEMPERATURE. 

 Specific Heat. 



Various forms of Calorimeter. [Black, Wilke, Regnault, Bun- 

 sen, &c.] 



Specific Heats of Air and other Gases at Constant Volume and 

 at Constant Pressure. 



Methods of Joule and Regnault. 



Velocity of Sound. 



Tone of Organ-pipe filled with different gases. .... 



(d) ELECTRIC EFFECTS. 



Electricity produced by heating Crystals, &c. [Haiiy, Hankel, 

 Thomson, &c.] 



Electric currents produced by unequal heating in non-homo- 

 geneous circuits. Thermo-electricity. 



When one of the junctions of a closed circuit of two metals is 

 raised to a higher temperature than the other, a current of elec- 

 tricity passes round the circuit and increases in intensity with 

 increasing difference of temperature of the junctions. The 

 direction of the current is, of course, reversed if the cold junction 

 be now made the hotter. [Seebeck.] 



In certain cases, as in circuits of iron-copper, iron-silver, iron- 

 gold, &c., the current increases more and more slowly for succes- 

 sive equal increments of temperature difference of the junctions, 

 attains a maximum, gradually diminishes, and finally is reversed 

 in direction. [Gumming.] 



When a current of electricity from an external source passes 

 through a junction of two metals, it causes an absorption or dis- 

 engagement of heat. If the direction of the current be the same 

 as that which would be produced by heating the junction, the 

 result is absorption. [Peltier.] 



Thomson showed theoretically that the Peltier effect is insuffi- 



