48 



r>l. J. A. HAKKER AND P. CHAPPUIS ON A 



mounted on wood, was not found to be quite perfect as regards insulation. The new 

 key, which along with the thermometers and nearly all the accessory apparatus was 

 obtained from the Cambridge Scientific Instrument Company, Limited, is shown in 

 fig. 3, and in the general plan of the auxiliary apparatus (fig. 4). It is provided with 



Fig. 3. 



Fig. 4. 



ebonite pillar insulation, and the four levers are rearranged in their order, the two 

 forming the galvanometer-contacts being supported from the same pillar one under 

 the other. All the contacts in the key are of platinum. An adjustable steel spring 

 under the topmost lever helps to hold it up against the contact screw above, thus 

 ensuring good contact in the galvanometer-circuit when the key is released. 



XII. ACCESSORIES TO THE RESISTANCE-BRIDGE. 



The battery, reversing-switch, key, and external resistances were all enclosed in a 

 wooden case provided with a glass lid, the necessary handles for the adjustments and 

 for working the keys, projecting through the sides, and the whole being kept nearly 



