1878.] 



Contact Theory of Voltaic Action. 



223 



being cut from the same piece of metal; C is bent upwards and passes 

 through, an orifice in the bath. The wire from "D to the insulated 

 electrode of the electrometer is protected by a wide tube of metal ; 



this tube, the outside of the electrometer, and the uninsulated electrode 

 being connected with B. A double door (not shown in the figure) gives 

 access to the inside of the bath. HGrH is a wooden support which may 

 be withdrawn from the bath. E and F are thermometers of which the 

 "bulbs are near the surface of the paraffin. The difficulty of determin- 

 ing exactly the temperature of the paraffin wax arose from its non- 

 condiictivity ; and the use of a third thermometer, passing through a 

 tubulure horizontally underneath B, was found to add nothing to the 

 accuracy of the temperature readings. 



To obtain continuous time readings of the electrometer, we let the 

 image of the cross fibres of our lamp slit formed by the mirror fall on 

 a horizontal wooden roller covered with paper. This roller was 100 

 centims. long, and 13 centims. in diameter. A clock causes the roller 

 to make a revolution in two minutes. We are able suddenly to change 

 the rate of this roller to one revolution in 7' 2 minutes, and we can 

 also slightly vary the rate by altering the length of the pendulum. 

 The image of the cross fibres is easily followed in its motion on the 

 paper by a pencil. When the paper is cut off at any place parallel to 

 the roller-axis it exhibits the time observations in a compact form well 

 adapted for calculation. The clock being stopped and a scale attached 



