486 



should be thickly coated with shellac varnish which, after drying, should 

 be baked on by heating until it begins to smoke. Mercury cups made in 

 this way have been in use in our laboratory for twenty years and are still 

 doing good service. 



The figure practically explains itself. By means of the links, L and 

 L prime, the apparatus can be connected with any calibrated bridge wire, 

 thus adapting it to the Carey Foster method. By changing the thick 

 connectors, C and C prime, to the dotted positions it will be seen, by 

 tracing the connections, that the resistance in the gaps, B and B prime, 

 are interchanged to opposite ends of the bridge wire. These gaps can be 

 adjusted to any width by means of the slotted support shown in the 

 figure. A piece of mica, M, is used to separate the strips at the point of 

 crossing. 



As the conductors are so arranged that the arms of the bridge are at 

 all times symmetrical, the dimensions of the apparatus are immaterial. 

 However, a scale of centimeters is added as a suggestion of size for those 

 who may care to construct apparatus of the size figured. It might be 

 added, that apparatus similar to the above has been used at the DePauw 

 physics laboratory for a number of years and has proved very satisfactory 

 for student work. 



