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III. On the Thermal Effects of Fluids in Motion/' By J. P. 

 JOULE, LL.D., F.R.S., and Professor W. THOMSON, LL.D., 

 F.R.S. Received May 9, 1860. 



In our paper published in the Philosophical Transactions for 1854, 

 we. explained the object of our experiments to ascertain the differ- 

 ence of temperature between the high- and low-pressure sides of a 

 porous plug through which elastic fluids were forced. Our experi- 

 ments were then limited to air and carbonic acid. With new appa- 

 ratus, obtained by an allotment from the Government grant, we have 

 been able to determine the thermal effect with various other elastic 

 fluids. The following is a brief summary of our principal results at 

 a low temperature (about 7 Cent.) . 



Further experiments are being made at high temperatures, which 

 show, in the gases in which a cooling effect is found, a decrease of 

 this effect, and an increase of the heating effect in hydrogen. The 

 results at present arrived at indicate invariably that a mixture of gases 

 gives a smaller cooling effect than that deduced from the average of 

 the effects of the pure gases. 



