446 On the Lateral Diffusion of a Current in a Conductor, 



upper half of the sheet is given ; i. e. if the whole sheet were 

 given, the second half would lie lower down on the page. The 

 slight irregularities in the curves are no doubt produced by va- 

 riations in the thickness of the tinfoil. 



Breadth =27'6centims. 



The method of making contact with the tinfoil and marking 

 the centre of the place of contact was follows : — The wires from 

 the terminals of the galvanometer were attached to two thin brass 

 rods with blunt conical points 3 millims. in diameter, a was 

 straight, and had a needle-point projecting about 1 millim. from 

 the centre of its blunt point, a was held in a clip and placed 



To galvanometer. 



|F^~ 



iTo battery. 



vertically on any part of the tinfoil through which it was desired 

 to trace an equipotential line, so that the whole of the blunt 

 point made contact, and the needle-point made a dot in the 

 centre of the contact. It is now required to move j3 about on 

 the tinfoil till there is no deflection (i. e. till it is in the same 

 equipotential line as a), and then, and not till then, to make a 

 dot in the centre of the contact. The way in which this was 

 managed may be seen by looking at the figure. /3 is bent twice 

 at right angles, so that it is only about 20 millims. from the 



