CONTINUOUS ELECTRIC CALORIMETRY. b 7 
The advantage of this particular arrangement was partly that of expedition and 
convenience, partly that of avoiding systematic errors due to changes of condition or 
temperature while the calibration was proceeding. The construction of the vernier 
dial, 100 coils of 20 ohms each, made it a good standard of comparison, as there was 
no risk of appreciable heating from the current employed, although it was necessarily 
kept on for more than an hour. Moreover, as it was constructed of similar wire and 
enclosed in a similar box to the main dial, it was probable that any change of the 
surrounding conditions of temperature would affect the two similarly. The heating 
effect of the current on P and Q would be sufficiently eliminated by their similarity 
of construction. 
Readings taken in this manner, with the slider set in each position of the main 
dial, gave 100 equations of the following form :— 
R« + R«+i = SP/Q + d n /s .(1). 
To determine the correction at each point of the main dial, and the relative values 
of the 101 resistances and the vernier dial, it was also necessary to determine the 
ratio of any two of the coils to each other, and the ratio of the two together to the 
vernier dial. This was effected by the method of interchanging, as already described 
for determining the ratio of the two halves of the slide-box. 
The ratio of coils R t and R., to the vernier dial S was found to be 
(R 2 + R 2 )/S = P000039. 
The ratio of coils R : and R 2 to each other was found to be 
Pvj/Ro = P000400. 
In the latter case the galvanometer contact was made by means of a copper wire 
to the stud between 1 and 2, the glass cover being removed for the purpose of 
this test. 
The observation of the values of the deflections d for the 100 equations of the 
type (1), was repeated on two sejjarate occasions. On the first occasion the 
110,000-ohm galvanometer was employed, but it was found that when the galvano¬ 
meter was adjusted to a suitable degree of sensitiveness for the experiment, its time 
period was too slow, and its zero not sufficiently constant to give the best results. 
It took upwards of an hour to obtain the first fifty observations. This series was 
not therefore continued throughout the box, but the observations were reduced to 
mean ohms of the box by reference to the value of the correction at the middle 
point of the box obtained from a separate observation. On the second occasion the 
110,000-ohm galvanometer was replaced by one of 2000 ohms resistance, which 
was better suited for this particular exjDeriment, though not so well adapted for 
observations in which the whole box was employed. The sensitiveness of this 
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