12 



Prof. J. Tyndal] on 



[Dec. 18, 



thermometer, whose bulb was in contact with the bottom of the brass 

 vessel. 



" The following table gives the chief results of some of the experi- 

 ments carried out in this manner. The figures of the column marked 

 T record for each of the stated gases the temperature of the water : — 

 First, at the commencement of the experiment ; secondly, after mixing 

 the hot and cold water ; and thirdly, at the moment when the deflec- 

 tion of the needle was at its maximum. The differences between the 

 first and third figures are given under t, whilst t shows the corre- 

 sponding deflections, whose real and comparable values are placed in 



brackets underneath them The figures under z express 



in minutes the time from the beginning of the experiment until the 

 junction reached its maximum temperature. The tension of the gases 

 in the interior of the glass cylinder is given in millimetres under j? ; 

 and, finally, the last column contains comparable values expressing 

 the intensity of the thermal action at the junction." 





T. 



t. 









100 T. 





r. 





p. 



t. 





19-8 











760 







56-0 













47-7 



27*9 



50-5 

 (99 -25) 



22 



55 



356-6 





18-4 













15 







54-6 















47-0 



28-6 



48 -0 

 (88 -5) 



15 



» 



309 -5 





22-5 













760 







57 -5 















50-5 



28 -0 



57*8 

 (130 -6) 



>17 



55 



466-4 



r 



23 

















Rarefied hydrogen. . . «| 



58-0 















52-1 



29 -1 



53-0 

 (110 -o) 



14 



55 



378-0 



I interpret thus the method here pursued : — Suppose, for the sake 

 •of simplicity, the thermometric zero at the bottom of the brass vessel 

 to correspond, at starting, with the galvanometric zero, and supposing 

 the temperature of the bottom of the brass vessel to augment within 

 certain limits ; then, so long as the differences remained small, the 

 quantity of heat received by the soldered junction would be propor- 

 tional to the difference of temperature between the junction and the 

 source. When, under such conditions, the galvanometric degrees, or 

 rtheir values, are divided by the thermometric degrees, a constant 

 quotient ought to be obtained. If, on interposing any gas between 

 the source and the junction, the quotient referred to were observed to 

 .change, such change would express the action of the gas ; while the 



