416 



Mr. J. H. Reeves on an Addition 



required a slide-wire bridge, which may be of a rough descrip- 

 tion but should have a resistance of an ohm or so. At the end 

 of the paper it is shown how this latter and the Addition 

 can be united in one. 



The whole arrangement is joined together as shown in 

 fig. 3, the dotted lines indicating the temporary connexions. 

 By comparing this with figs. 1 and 2, no detailed description 

 is necessary, as R, r, x, y, a, b, s are lettered to correspond. 



The battery may with advantage be a storage-cell with two 

 resistances in series with it. One, p, may be an adjustable 

 carbon resistance, while p l may be constructed of wire and 

 should have a considerable resistance. This latter terminates in 

 mercury cups m and n, so that by joining these cups together 

 with a short connector the resistance can be easily short- 

 circuited. 



The resistances x and y are resistances unplugged from the 

 box of coils forming the ordinary Wheatstone bridge ; y is 

 the 1000-ohm coil of one of the ratio arms, and x is in the 

 adjustable arm. If such a set of coils be not available, y may 

 be any 1000-ohm coil, and x any box of coils containing 

 resistances up to 5000 ohms. The two leads joining x and y 

 to B and B' respectively should be as stout and short as 

 possible. The resistances from d, d' to I form the a b of 

 fig. 2. 



To make a measurement, insert the wire whose resistance 

 is required in its proper clamps, taking care that it lies quite 

 straight between them. Its diameter and material being 

 known, the resistance of one metre of it can be approximately 



