Platinum Thcrmometry at Kew Observatory. 



47 



44. We have next to consider the constancy of the fundamental 

 intervals. Corresponding ice and steam point observations were almost 

 invariably taken in immediate succession to one another, so that 

 ordinary changes in the leads could hardly affect the results. I have 

 divided the data into groups according to the date, and give only the 

 mean results. In the first group there' were only two observations 

 and in the last group only three, except in the case of KI and K 5 , 

 where five observations had been made. In the three intermediate 

 groups the means are nearly all based on six observations. A few 

 observations made in the early part of 1897 have been wholly omitted, 

 as the state of the leads was certainly not then satisfactory. 



Table XVI. Mean Values of Fundamental Intervals at different 



Epochs. 



According to the table there is a fall in the fundamental interval of 

 every thermometer between 1896 and 1899. It is probable, however, 

 that this is mainly if not entirely fictitious except in the case of KI. 

 When the resistance box was altered in the summer of 1897, the coils, 

 as Table IV shows, were slightly disturbed ; and in all probability the 

 mean box unit was slightly altered. An increase in this unit of about 

 35 parts in 100,000 would account pretty satisfactorily for the apparent 

 differences in the results of the second and third epochs of the table. 



During the third and fourth epochs nothing happened to the box, 

 and Kj is the only case where there is any noteworthy difference 

 "between the corresponding means in the two epochs. 



Between the fourth and fifth epochs the coil I broke, and its resist- 

 ance was diminished by about 0'66 of a box unit by the resoldering. 

 This fact, and the comparatively small number of observations on 

 which the means are based during the fifth epoch, predispose me to 

 query the apparent falls in the fundamental intervals of K 3 and K 4 . 

 In the case of K x , however, the fall is too large to be explained away. 



45." Instead of attempting to trace changes in the ice-sulphur 



