218 Mr. F. W. Burstall on the Use of 



in the first instance by placing the standard 1 ohm coil in 

 parallel with a coil of slightly smaller resistance than the 

 bridge-wire. This gave the resistance per scale- division of 

 the wire as '00087 at 10°-1. After the value of the ^ ohm 

 coil had been found, the resistance of the bridge-wire was 

 determined by balancing the -j^ ohm coil against a coil of 

 slightly smaller resistance than the bridge-wire ; the j 1 ^ ohm 

 coil was then removed, and the gap short-circuited The 

 actual figures are of interest as showing the value of a cali- 

 brated wire. 



*1 ohm in A. Gauge in D. Temperature 10 o, 8. 



Reading 394-0. 



Correction for calibration —'3. 



Short circuit in A. Gauge in D. Reading 967*9. 

 Correction for calibration, — *2. 



Hence, if p be the resistance per scale-division, 



•1 ohm coil=2x 574p = 1148 p. 



On interchanging the coils, — 



•1 ohm in D. Gauge in A. 

 Reading 32*9. Correction for calibration, 0. 



Short circuit in D. Gauge in A. 

 Reading 607*0. Correction for calibration, — *1. 



This also gives 



•1 ohm coil =1148/3. 



Whence p = '00008705 at 10°*8. 



A and D being the two outer gaps of the bridge. 



The 100 and 1000 ohm standard coils were determined on 

 similar bridges. The 100 ohm coil, — 



On April 14, had a value 99-913, at 10°'8. 

 „ „ 17, „ „ 99-964, „ 12*5. 



Whereas it should have been 99*960, according to the 

 observation on the earlier date. This discrepancy is, I 

 believe, due to the fact that the shunt required on one of the 

 10 ohm coils forming the bridge was greater than 12,000 

 ohms, which was the largest resistance at my disposal : in 

 order to obtain a balance one of the 10 ohm coils had to be 

 warmed, by means of a water-bath, about 2° above the tempe- 



