486 Prof. A. Schuster on the Scale-Value of 



groups according to the temperature at which the thermometer 

 had been kept, and I have divided them into three periods. 







First Period. 









March 30 to April 7, 



1892. 



- 



Average temperature to 

 which the thermometer 

 had been exposed. 



Number of 

 Observations. 





Mean zero, 



o 



8-6 





2 





23-47 



12*9 





4 





23-41 



17-1 





2 





23-36 



30-9 





1 

 Second Period. 





23-05 



o 



Mi 



arch to June 1893. 





13-7 





1 





23-19 



17*6 





3 





23-31 



23-3 





3 



Third Period. 





23-32 



o 





June 22, 1894. 







17 





1 





23-35 



The first observation of the second series does not fit in 

 very well with the others, but if it is remembered that a tenth 

 part of a division means only 0°'004, the general agreement 

 must be considered satisfactory, and the first series, which is 

 perhaps the one in which the greatest care was exercised, 

 shows the gradual lowering of the freezing-point very 

 decidedly. The numbers show that the changes of zero are 

 no longer appreciable. I have added to Table III. those of 

 my observations w T hich were taken after the thermometer had 

 been exposed to about 17°. 



The Pressure Correction. 



As the chief object of this investigation was to find the 

 scale-value of the thermometer A under the conditions holding 

 in Joule's experiment, the most natural manner of proceeding 

 would have been to compare it in the vertical position with 

 some standard instrument. Owing to the great length of the 

 thermometer it was not found possible, however, without 

 much inconvenience to construct a vessel into which it 

 could entirely be plunged vertically, and if only partially 

 immersed the uncertain stem corrections would take away 



