34 



Dr. C. Chree. Investigations on 



tin- rapidity of attaining the steady state in ice depended greatly on 

 the tightness of the packing and the moistness. Thus, particulars 

 are given of experiments made with the ice variously treated 



Table XI. 



Most of the data are based on at least two experiments. The 

 different experiments with any one thermometer in steam were in good 

 agreement. The agreement in the ice experiments was pretty fair 

 when the ice was moistened or was tightly packed ; when, however 

 the ice was not freshly moistened and was only loosely packed the 

 results were very variable. The intervals 1, 0'5 were generally only 

 approximate, and to elucidate the exact law of cooling or heating 

 would require a more complete investigation. The data are, however, 

 exact enough for general conclusions. 



The most striking fact is the extreme slowness of all the platinum 

 thermometers as compared to the two mercury thermometers ; and it 

 should be noted that these two thermometers are not of a type intended 

 to be rapid. 



To get within 1 of the steady reading, the temperatures of the 

 thermometers had to alter about six times as much in steam as in ice. 

 The times required for these two changes are pretty much alike in all 

 the platinum thermometers, supposing the ice tightly packed, as it 

 usuilly is in the normal experiments. Thus the approach to the steady 

 state is decidedly slower in ice than in steam, and a longer time must 

 be allowed in the former case than in the latter. 



31. Some rough calculations, based on the observations with KI, 

 summarised in Table XI, point to the conclusion that 3*5 minutes' im- 

 mersion in ice and 2 '5 minutes' immersion in steam would suffice to bring 

 the reading within 0'0005 of its stationary value in the case of this 

 thermometer. K and K 6 are decidedly less rapid, and I should con- 

 clude that ten minutes' immersion in well-packed ice and five minutes' 

 exposure to steam are by no means very excessive allowances in the 



