484 Mr. J. P. Joule and Prof. Thomson on the Thermal Effects 



times the whole of the narrow india-rubber tube, the wooden pin- 

 cers, and several inches of the wider tube containing the thermo- 

 meter, wei-e kept below the surface of the bath, and still the coohng 

 effect was observed ; and this even when hot water, at a tempe- 

 rature of about 150° F., was used, although in this case the 

 obseiTed cooling effect was less than when the temperature of 

 the bath was lower. 



As it was considered possible that the cooling effects observed 

 in these experiments might be due wholly or partly to the an* 

 reaching the thermometer-bulb before it had lost all the vis viva 

 produced by the expansion in the narrow passage, and conse- 

 quently before the full equivalent of heat had been produced by 

 the friction, and as some influence (although this might be 

 expected to diminish the cooling effect) must have been produced 

 by the conduction of heat through the solid matter round the 

 air, especially about the narrow passage, an attempt was made 

 to determine the whole thermal effect by means of a calorime- 

 trical apparatus applied externally. For this purpose the india- 

 rubber tubes were removed, and the stop-cock was again had 

 recourse to for producing the narrow passage. A piece of small 

 block-tin tube, about 10 inches long, was attached to the mouth 

 of the stop-cock, and was bent into a spiral, as close round the 

 stop-cock as it could be conveniently arranged. A portion of 

 the block-tin pipe was unbent from the principal spiral, and was 

 bent down so as to allow the stop-cock to be removed from the 

 water-bath, and to be immersed with the exit spiral in a small 

 glass jar filled with water. The forcing-pump was now worked 

 at a uniform rate, with the stop-cock nearly closed, for a quarter 

 of an hour, and then nearly open for a quarter of an hour, and 

 so on for several alternations. The temperatures of the water 

 in the large bath and in the glass jar were observed at frequent 

 stated intervals during these experiments ; but, instead of there 

 being any cooling effect discovered when the stop-cock was 

 nearly closed, there was found to be a slight elevation of tem- 

 perature during eveiy period of the experiments, averaging 

 nominally -0652^3° F. for four periods of a quarter of an hour 

 when the stop-cock was nearly closed, and '06533° when it was 

 wide open, or, within the limits of the accuracy of the observa- 

 tions, '065° in each case ; a rise due, no doubt, to the rising 

 temperature of the surrounding atmosphere during the series of 

 experiments. Hence the results appear at first sight only nega- 

 tive ; but it is to be remarked that, the temperature of the bath 

 having been on an average 3i° F. lower than that of the water 

 in the glass jai-, the natural rise of temperature in the glass jar 

 must have been somewhat checked by the air coming from the 



