I>r. II. T. n.-imr.. Un tl. ' /.' 



ami in addition a specially constructed rheostat, by which 

 sma.ll adjustments to the circuit could IKJ made for regulating the heat 

 supply. 



The ipeasiirenient of the different constants entering into the 

 general difference equation of the method is treated of under two 

 heads, Electrical and Thermal. In the first, the Clark cell and resist- 

 ance form the principal measurements, and in the second the measure- 

 ment of temperature, time, and weight have to be considered. An 

 exceedingly accurate potentiometer was employed to determine the 

 difference of potential across the resistance and calorimeter in terms 

 of the E.M.F. of the Clark cell. 



nful Proof of the Theory of the Method. 



In this section the author shows that the dependence of the heat 

 loss per degree rise in the calorimeter varies in a linear relation to the 

 flow in proportion to 4'2 QS beyond certain limits of flow, and that 

 this is essential for the fulfilment of the theory of the method. For 

 very small flows the conduction effect at the outflow end, due to the 

 rise of temperature in the water, appears and causes the line repre- 

 senting the relation of heat loss to flow to approach an infinitely large 

 value of the heat loss for a zero flow. The limits of flow chosen in the 

 present measurements are safely included within the linear relation. 



The relation of the heat loss to the rise of temperature shows that 

 for rises of from 2 to 8 and beyond, the heat loss is directly pro- 

 portional to the rise. The thermal capacity of the calorimeter is cal- 

 culated, and it is shown that for the small changes in the temperature 

 of the calorimeter during an experiment this is negligible. 



Effect of Stream-line Motion. 



Some of the earlier results are given in this section, showing the 

 effect of stream-line motion on the distribution of heat throughout 

 the water column for a calorimeter with a 3-mm.-bore flow tul>e for 

 different flows. The temperature of the heating wire used for these 

 experiments is also calculated, and found to vary considerably when 

 moved from the centre to the sides of the tube. It was found neces- 

 sary to thoroughly stir the water in its passage through the flow tube, 

 in order to ensure a perfectly uniform temperature throughout the 

 water column. 



Preliminary Measurement*. 



The preliminary measurements of the value of J, which were made 

 in the summer of 1898, were affected by the presence of stream-line 

 motion in the tube, as at that time no device was introduced to 



