326 THE ELECTRO-MOTIVE POWER OF HEAT. [MEMOIR XXIV. 



copper and iron wire soldered thus together will indi- 

 cate temperatures. 



In the arrangement now described, when an experi- 

 ment has to be made, the vessel A A is to be filled 

 two thirds full of water, the bulb of the thermometer 

 being so adjusted as to be in its middle, the soldered 

 extremity S of the two wires being placed in contact 

 with it, and a small cover with suitable apertures ad- 

 justed on the top of the vessel, so that the steam as it 

 is generated may rush up alongside of the tube of the 

 thermometer and bring the mercurial column in it to 

 a uniform temperature. If the extremity of the thermo- 

 electric pair be allowed to rest on the bottom of the 

 glass vessel, no accurate results can be obtained ; the 

 pair does not then indicate the temperature of the 

 water. The commxinicating wires ff are then placed in 

 the cups, the trough e filled with water and pounded ice, 

 and carefully surrounded with a flannel cloth. The wa- 

 ter in the vessel A A is then gradually raised to the 

 boiling-point by means of a spirit-lamp, and kept at that 

 temperature until the galvanometer needles and the ther- 

 mometer are quite steady. The same plan must be fol- 

 lowed when any other temperature than 212 is under 

 trial, for the thermo-electric wires changing their temper- 

 ature more rapidly than the mercury in the thermom- 

 eter, it is absolutely necessary to continue the experi- 

 ment for some minutes to bring both to the same state 

 of equilibrium. 



When a temperature higher than 212 Fahr., but un- 

 der a red heat, is required, I substitute in place of the 

 vessel A A a tabulated retort, the tubulure of which is 

 large enough to allow the passage of the bulb of the 

 thermometer and the wires. A quantity of mercury, 

 sufficient to fill the retort half full, is then introduced, 

 and the tubulure being closed by appropriate pieces of 



