Platinum Thermomctry at Kew Observatory. 



11 



They were repaired by the Instrument Company, and on their 

 return in September, 1897, a large discontinuity was observed in the 

 values of E in the platinum thermometers. I then found that inter- 

 changing the leads caused a difference of fully 1 in the reading. This 

 seeming unsatisfactory, the leads were readjusted by the Instrument 

 Company, and we assured ourselves of their approximate equality, 

 without, however, attempting to measure the exact difference. As 

 the leads remained satisfactory to the eye, no more attention was 

 given to the matter until the autumn of 1898, when a conspicuous 

 drift appeared in the values of K . Experiment then showed that the 

 difference between the leads was liable to large fluctuations ; accord- 

 ingly new leads were got from the Instrument Company in December, 

 1898. These had been adjusted with great care, and on their arrival 

 at Kew they were found to be very nearly though not exactly equal. 



Table III gives a brief synopsis of our experience with the leads. 

 The quantity tabulated is the excess of the box reading obtained the 

 thermometer being in ice, steam, or sulphur vapour when the CU 

 leads were connected to the thermometer over the reading when the 

 PP leads were so connected. 



Table III. Effect of Interchanging Leads. 



Each experiment consisted of at least two readings with each 

 arrangement of the leads. 



The resistance of one pair of the new leads was recently found 

 by Dr. Harker to be approximately 0'07 ohm at atmospheric tern- 



