RECENT PROGRESS IN PHYSICS. 395 



To measure the heat produced hy the galvanic current in a metallic 



ire, Lenz used the apparatus represented in Fig. 47. 



In the middle of the board is fastened the ^'s- '^^* 



lass stopper B, ground to fit into the neck 

 fa glass jar which, by means of some grease, 

 aay be fitted upon it air and water-tight. 

 ^ brass clamp, omitted in the figure, presses 

 he lower rim of the neck of the jar to the 

 )oard, so that it cannot be displaced even by 

 dolent motions of the apparatus. The jar 

 las ground in its bottom a cylindrical hole, 

 nto which the fluid can be poured, and 

 'lihrough which, also, a thermometer can be 

 inserted by means of a cork. The thermom- 

 eter used was divided to 4^ of a degree. Two 

 pieces of wire of about 1 line in diameter are 

 passed through perforations in the glass stopper and ceuiented there. 

 'Their upper extremities projecting into the jar are somewhat conical, 

 and made of platinum ; these platinum cones are soldered to copper 

 wires of equal diameter, which, let into the board, pass to the screw- 

 clamps s, into which the conducting wires from the poles of the battery 

 are screwed. The wire to be heated is previously coiled into a spiral 

 around a cylinder of 1 — 2 lines in diameter, and has its ends clamped 

 upon the cones by means of two little pieces of platinum. It remains 

 erect by its own elasticity, its coils not touching anywhere. 



The fluid with which the jar was filled, so far at least as en- 



' tirely to cover the wire-spiral, was spirit of wine containing 85 to 86 



' per cent, of alcohol, for water is so good a conductor that a part of the 



current would pass through it and not through the wire, as becomes 



immediately apparent from the feeble evolution of gas. 



After the wire-spiral was properly fastened and a measured quantity 

 of spirit of wine poured into the jar the apparatus, together with the 

 multiplier (Nervander's tangent compass) and the rheostat, were 

 inserted in the circuit of a Daniell's battery. By means of the rheo- 

 stat the current was always kept at a constant strength ; and then the 

 time required to raise the thermometer in the spirit of wine a certain 

 number of degrees was noted. By turning round the apparatus in a 

 small circle, the fluid was made to rotate, whereby an equal distribu- 

 tion of the temperature throughout its mass was produced. 



In order to avoid the errors arising from the loss of heat to sur- 

 rounding bodies, the spirit of wine was previously cooled below the 

 temperature of the air, and the experiment finished when its tempera- 

 ture was just as many degrees above that of the surrounding air as it 

 had been below it at the commencement. 



To give a clear idea of the course of the investigation, the individual 

 steps for one series of experiments will be described at length. 



The temperature of the air being 16° R, the spirit of wine was 

 cooled by means of ice down to 7° and poured into the jar ; the circuit 

 was closed and the needle by means of the rheostat constantly kept at 

 35° ; next, with a watch marking seconds, the exact instant was ob- 

 served when the temperature of the spirit was 10, 11, 12, 13, 14, and 



