132 DR. K H CKIFFITHS AND MR. EZER GRIFFITHS ON THE 



that an error of O'l bridge-wire division (= 0'007 Pt) in the estimation of the zero 

 I>oiiit would affect conclusions derived from an experiment of average length by the 

 total heat method by (in the case of Cu, for example) 5 parts in 9000. In our 

 earlier " total heat " experiments we had not realized the importance of this zero 

 reading, and this no doubt is the cause of certain discrepancies. 



The position of the zero point was, however, of little importance when the 

 intersection method was adopted, for so long as the temperature of the reference 

 block remained unchanged, the effect of any alteration in the zero point was self- 

 eliminated. 



The method of reduction is shown by one example, namely, that of copper at C., 

 with thermometers AA, BB. 



The only reason which has guided us in the selection of this out of the 48 similar 

 groups, is that it happens to be first of the groups given in Table XI. The large 

 amount of arithmetic involved in the reduction of our observations is well illustrated 

 by this example. 



Explanation of Tables. 



n = number of standard cells balanced on heating coil. 



Column I., bridge readings. The successive points on bridge wire across which 

 transits were taken. 



Column II. (t ). Times of transit from chronograph tape. 



Column III. (St). Interval between successive transits. (If transits observed every 

 l bridge wire, as in Experiment IV., then St for 1 bridge wire calculated.) 



Column IV. (Se). Value in Pt degree of bridge- wire division corresponding to St. 



Column V. (^ x 10 7 ). 

 \ot I 



Column VI. (0). Temperature at mid-point of SO, measured from centre of bridge 

 wire. 



Column VII. The letters denote the values of Sd/St taken in pairs, for the purpose 

 of obtaining the slope of the line. 



Column VIII. Change in S8/St for equal intervals of temperature. 



