3G4 



MESSRS. B. T. GLAZEBROOK AND T. C. FITZPATRICK 



to the bridge by copper rods, and rods of the same material and almost the same 

 resistance were used to connect the standard coils. It was hoped in this manner to 

 compensate the effect produced on the resistance of these rods by changes of tempera- 

 ture in the room. Since the difference between the two sets of rods was only 

 equivalent to one bridge wire division, this was completely secured. 



The coils used were the following : For the tubes VI. and VIII. the standard F 

 was employed ; for V. and IX. the standards F and G in multiple arc ; and for I. and 

 III. F, G, and Flat in multiple arc. 



In the case of the legal ohm, tube II., a coil of 100 B.A. units, ELLIOTT No. 68, 

 was placed in multiple arc with the tube, and the difference between the combination 

 and F was found in the usual way. The temperature of the water baths in which 

 the coils were placed was taken with a thermometer which had been compared at 

 Kew, and the necessary corrections applied. The temperature of the baths and of the 

 room in which the experiments were made never differed greatly from 10. The 

 following Table VI. gives the values of the coils at 10, with their temperature 

 coefficients. The value of F and G are taken from Dr. FLEMING'S chart. The differ- 

 ence between the two coils at the time of the observations was determined and found 

 to agree exactly with that given by the chart. In the case of Flat, which is not one 

 of the six coils mentioned on p. 352, repeated observation during the last two years 

 has shown that it is now slightly lower relatively to the others than when examined 

 by Dr. FLEMING ; the change is not greater than '0001 B. A., unit, and is probably due 

 to a slight imperfection in the insulation. We have taken the value relative to F and 

 G given by our own observations ; as Flat is only used in multiple arc with F and G 

 for the tubes I. and III., any uncertainty in its value is divided by nine in the result, 

 and the error introduced is too small to trouble us. 



The coil of 100 B.A. units is one of the standards of the Association, and, like the 

 other coils, is of platinum-silver wire. 



TABLE VI 



For the one unit tubes the terminals of F dipped into mercury cups on ebonite, 

 which were connected to the bridge by the copper rods above mentioned. When the 

 coil G was used its terminals dipped into the same cups, and for the one-third unit 

 tubes I. and III., the coil Flat dipped into two other cups connected with the first 

 two by thick pieces of copper. The resistance of these connexions was determined 



