for obtaining a Constant Temperature, 

 Observation II. 



93 



Time of 



Reading 



Current on 



Obs. 



of 



Thomson 



Thermometer. 



Balance. 



h in 



o 



centiainperes. 



7 04 



25-37 



36-00 



7 16 



25-38 



,, 



Current 



temporarily 



increased. 



7 29 



25-57 



3600 



7 33 



25-57 



!! 



7 53 



25-57 





8 03 



25-575 



„ 



8 13 



25-58 



>? 



8 20 



25-585 





Current 



temporarily 



increased. 



8 29 



25-67 



36-00 



8 33 



25-67 



,, 



8 43 



25-67 



}f 



8 53 



2567 



}J 



9 03 



25-67 



„ 



9 13 



25-675 



»> 



9 23 



25-68 





9 33 



25-685 



- 



These observations were made during the past summer in 

 the Physical Laboratory of Haverford College. 



From the first set it will be seen that the temperature was 

 held constant within yj^ of a degree for three quarters of an 

 hour ; in this case no cotton packing was used. 



In the second set it will be observed that the condition of 

 steady flow has not quite been reached, for the temperature 

 continues to rise slowly. Nevertheless, there are two separate 

 intervals of more than 40 minutes each, during which the 

 variation does not exceed y^ of a degree. 



I regret having had to leave the laboratory before 1 could 

 make further experiments, for I feel confident the method is 

 able to give much greater constancy. 



Its chief advantages are that it can be applied to a vessel 

 of almost any shape in almost any position. This feature 

 makes it especially valuable for the determination of coeffi- 

 cients of expansion by the method of Boguski described in 

 the Zeitschrift f. phys* Chem. ii. p. 482 ; in fact, it was for 

 use in this problem that the method was devised. 



Unlike the method of vapour baths, it will give any tem- 

 perature desired. This temperature can be obtained by trial 

 very quickly, without previous experiment, or the calorimeter 

 can be calibrated and the ampere-balance set for the correct 

 current at once. 



Lick Observatory. 

 October 1891." 



