84, 8.88 and 6.66 standard ohms per statute mile respectively.
The balance is adjusted by shunting either AD or BD with a box, S, containing 20 to Ioo ohms. All the wires in the quadrilateral must be of the same metal as AB, to avoid accidental thermoelectric effects which would obscure the result.
In series with this set of coils is another set, S, which forms a measuring arm, the resistances of which are generally I, 2, 3, 4, 10, 20, 30, 40, 100, Zoo, 300, 400, woo, 2000, 3000, 4000 ohms. The junction between each pair of coils is connected as above described to a block, the blocks being interconnected by plugs all of which are made interchangeable.
Hence according to the magnitude of each coil the total resistance may be made anything from I to 9, 10 to 90, or 100 to goo ohms, &c. Three or four of the " dials " thus composed are arranged side by side, the brass blocks being mounted on a slab of ebonite and the coils contained in the box underneath, and they are so joined up that the central block of one dial is connected to the outside block of the next marked O.
By Ohm'S Law, And By The Definition Of Difference Of Electric Pressure Or Potential, We Obtain The Following Alternative Expressions For The Quantity Of Heat H In Joules Generated In A Time T Seconds By A Current Of C Amperes Flowing In A Wire Of Resistance R Ohms, The Difference Of Potential Between The Ends Of The Wire Being E = Cr Volts: H=Ect=Crt=E Z T/R.