488 



Prof. A. Schuster on the Scale-Value of 



1 have found it convenient to proceed in the observations 

 rather differently from the manner indicated by Guillaume. 

 The tube T is placed in a calorimeter containing about a litre 

 and a half of water, and that again is surrounded in an outer 

 jacket. The latter is filled with water about 2° above that in 

 the calorimeter, so that the thermometer is kept slowly rising. 

 The air-space in T being exhausted, a few observations are 

 taken at measured intervals of time, air is suddenly admitted, 

 and a further series of readings are taken, as in the following 

 example : — 



Observation. 



Time. 



Reading. 



Reading 







Pressure Gauge. 





h m 







1. 



2 15-5 



158-85 



72-6 



2. 



16 



158-85 





3. 



16-5 



159-05 





4. 



17 



159-17 





5. 



17-5 



159-30 





6. 



18 



159-35 





7. 



18-5 



159-40 





8. 



19 



163-60 







9. 



19-5 



163-70 





10. 



20 



163-75 





1]. 



20-5 



163-85 





12. 



21 



16395 





13. 



21-5 



161-05 





14. 



22 



164-20 





Taking the arithmetical mean between the first seven ob- 

 servations, it is found that the average temperature corre- 

 sponding to the time 17 m was 159*139, and by combining 

 the observations in pairs in the usual fashion we deduce the 

 average rate of rise per interval as *108. Hence 



159*139 + 4xl0*8 = 159*571 



gives the calculated reading at 2 h 19 m , but after the 

 seventh reading the air was admitted, so that the last seven 

 observations were taken at full atmospheric pressure. The 

 reduction being made in exactly the same fashion, another 

 reading is deduced for the time 2 h 19 m , viz., 163*583. 

 The difference betwen the two gave 4*012 divisions of the 

 thermometer as the effect of a change of pressure of 72*6 centim. 

 A number of observations of a similar character were taken 

 and are collected in Table IV. They were always so com- 

 bined that the observation at atmospheric pressure followed 

 that at reduced pressure. Otherwise a fall of the thermometer 



