t; I >r. ( '. ( 'hive. / 



expert. On thi< day observations were taken at the ice, steam, and 

 sulphur points, and on the same day observations were also taken with K 3 

 and K ( . Further, both Mr. Hugo and myself observed, each with two 

 sets of coils, at the ice and steam points, and our observations were in 

 excellent agreement. Thus I think the evidence is almost conclusive as 

 to the reality of a fall in the R and RI of K 5 , in consequence pre-um- 

 ably of its first exposure to the sulphur point temperature. Thi> fall 

 was apparently about 0'l in the case of RO. 



This is not the only case in which this phenomenon occurred. Thus 

 <m April 24, 1896, the thermometer K L , which had been freshly remade 

 after a breakage in silver, gave an R! of 356*507 immediately prior to a 

 sulphur point experiment, while on April 27, the value found for RI 

 was 356-404. There is no reason to suppose that any sensible change 

 in the leads had intervened. 



$ 43. Much the clearest evidence of sudden changes arises, however, 

 in the case of exposure to the temperature of molten silver. On 

 December 24, 1895, Ko was exposed to this temperature for the first 

 time at Kew,* the experiment being immediately preceded and suc- 

 ceeded by steam point observations. It was found that RI had 

 changed from 357-535 to 357*014, representing a fall of 0-52. On the 

 next trial in steam the value found for RI was 357*057 ; but as the RI 

 of K 3 and IM showed also a slight apparent rise during this interval, 

 the cause was most probably a sb'ght change in the leads. In March, 

 1896, Ko broke in silver -and was remade. After exposure to the tem- 

 perature of sulphur vapour on April 24, as already described, it was 

 tried in molten silver on April 27 ; on which occasion its R, fell from 

 356-404 to 356-050. After a second sulphur point experiment on June 

 '26, when no certain change occurred, Ko was tried a second time in silver 

 on July 2, and its RI again fell, though only by 0-15. Altogether, 

 l>etween April 24 and July 2, 1896, the R\ of K 2 showed a total 

 apparent fall of 0'735, whilst the corresponding mean apparent fall in 

 K 3 , K 4 , and K^, as obtained by interpolation, is only about 0*015. The 

 mean fall in these last three thermometers is doubtless a nearly correct 

 measure of contemporary change in the leads ; and we thus conclude 

 that two exposures to the sulphur point temperature and two exposures 

 to molten silver had produced a fall of approximately 0-7 in the zero 

 of K, 



The thermometer KI had been in molten silver in September, 1 895, 

 before it came to Kew. On its first exposure to molten silver at the 

 Observatory the exposure being as usual preceded and followed by 

 steam point observations the fall of Rj was only 0-08; and on two 

 subsequent occasions the effect, if an) r , was very small. For instance, 

 on the last occasion the apparent fall was only 0'009. 



* It was said to bare been heated in September, 1895, at Cambridge, to fully as 

 high a temperature. 



