71 



ments made with my present instruments indicate, show 

 any rise of temperature when a suitable measuring current 

 is sent through, though the same wire wound compactly 

 upon a piece of clay pipe rises considerably with this 

 current. 



The Wheatstone bridge and resistances which were used 

 are those I described before this Society,* and the arrange- 

 ment has proved very satisfactory when rapidity of 

 measurement is a consideration. The galvanometer is a 

 very good astatic which was bought for other purposes, 

 but being a short coil I was not working under ad- 

 vantageous circumstances, and am, therefore, making a 

 more suitable one. For the sake of any who may make 

 similar measurements I would advise a galvanometer shunt, 

 so that too much time may not be lost through swinging of 

 the needle during the balancing. Correction has to be 

 made for the temperature of the room, and as an open 

 window may not act as quickly upon the measuring coils as 

 upon a thermometer, this may from time to time be the 

 source of a small error. For very exact measurements the 

 temperature of the resistance bridge might be taken by 

 means of a small coil placed in melting ice. 



For laboratory, or observatory observations, there is no 

 doubt that this plan of taking the temperature may be 

 readily developed, so that an amount of exactness may be 

 attained which would be impossible by any other method. 

 Living in rooms in an hotel, it is rather awkward to have 

 delicate instruments left permanently in suitable positions, 

 and in this respect my previous instrument, with its simple 

 reader and ordinary compass galvanometer, which might be 

 moved about and hung up out of the way, was much less 

 troublesome to use. In that case, as I pointed out, the weak 

 point was the sluggishness of the thermometer, whereas 



♦ On a Method of Mounting Electrical Resistances : Proc. Manch. Lit. and Mill. Soc, 

 vol. xxiii., p. 43. 



