358 Mr. E. Wilson. The Kelvin Quadrant 



Fig. 1. 



forts en A/eeaf/e. 



beyond the range for which it is intended, since when the gauge is 

 in proper adjustment the value of C is only about 550 volts. 



In the following experiment the highest E.M.F. employed is 

 115 volts, and since a square root of mean square value equal to 

 100 volts was the maximum potential difference about to be used by 

 the author in a certain series of experiments upon alternate current 

 Watt-hour meters, it was necessary to see that within this range of 

 potential the formula above given is verified. The instrument was 

 connected as before with one pair of quadrants to the case, the other 

 pair being insulated and the electromotive forces applied to the 

 quadrants, as also to the needle, were supplied by storage cells, and 

 accurately measured by Poggendorff's method, the standard of com- 

 parison being Clark's cell. The results are given in Table I. 



The instrument in the above experiment was mounted on a slate 

 base in the upstairs room of the Siemens Laboratory. The spot of 

 light when working on this base with this instrument is never per- 

 fectly steady, and this may account for the errors observed in 

 Table I. 



Method of Test. 



Fig. 2 gives a diagram of connections showing how the electro- 

 meter was used as a "Wattmeter for alternate currents, and how it 

 was tested when being so used. In the formula 



= X(A-B)(C-^), 



