188 Dr. Schroeder van der Kolk on Gases. 



temperature, the second the heat to be added, and the third the 

 fall in temperature when no heat is added. 



Hydrogen. 



Thomson and Joule. 



A 



Addition Depression 



Temp. of heat, of tempe- Difference of pressure. 



Unit. rature. , A N Temp. 



0" 7^ metre. 1 metre. 



0-120 005 002 003 



Air. 

 -87 0178 1-08 



4 0-043 0-27 0-26 034 17 



100 0033 0-20 



Carbonic acid. 

 3 0-187 1-21 1-20 1-58 11 



100 0087 0-56 0-75 092 91 



Thomson and Joule have, as we know, determined the depres- 

 sion of temperature which takes place when a current of gas is 

 pressed through a narrow aperture, and have thus obtained tbe 

 results given in the last column. The fourth column gives the 

 depression of temperature which takes place at the temperature 

 given in the sixth column, when the difference of pressure is an 

 atmosphere. Comparing these numbers with those in the third 

 column, we see that they are tolerably proportional one to an- 

 other, especially if we take into account the differences in tem- 

 perature ; in the case of carbonic acid Thomson's number refers 

 to 91°, the preceding to 100°. This agreement in results obtained 

 in such entirely different ways may be regarded as a confirmation 

 of the theory. 



The numbers in the third and fourth columns cannot be 

 directly compared, since they refer to unlike differences of pres- 

 sure. The fifth column gives the cooling in Thomson and Joule's 

 experiments for a difference in pressure of a metre. Comparing 

 this and the third column, it is found that the cooling in the 

 direct experiments was always greater except in the case of hy- 

 drogen ; but the absolute value in numbers is in this case too 

 small to consider this an exception and not an error of obser- 

 vation. 



Yet a cause may be adduced for the constant difference in the 

 case of air and carbonic acid. The cooling observed by Thom- 

 son and Joule arises from three causes : — the internal work per- 

 formed in the passage from the initial to the final condition ; 

 the work which is performed in imparting to the issuing gas 



