140 JOEST RESEARCH WITH THOMS A. 



To the reprint in 1885 of the papers resulting from this 

 investigation, Joule prefixes the note containing the refer- 

 ence to his meeting with Sir William Thomson, a: Oxford, 

 already quoted, Chapter VIII. ; this note continues : — 



"My work with Thomson was chiefly experimental, 

 performed in Manchester and the neighbourhood. We 

 pursued the discussion of the thermal effects of fluids 

 in motion until the experiments were interrupted by the 

 action of the owners of the adjacent property, who, on the 

 strength of an obsolete clause in the deed of conveyance, 

 threatened legal proceedings, the cost of which I did not 

 feel disposed to incur/' 



This research was directed, in the first place, to verify a 

 conclusion resulting from the application of Thermo- 

 dynamics to Regnault's results. 



The researches of Regnault, published in 1847, while 

 they confirmed Boyle's law, that the density of air at con- 

 stant temperature increases in the direct ratio of the 

 pressure, to a much greater degree of accuracy than 

 was previously obtained, showed, nevertheless, that the 

 density increased slightly faster than the pressure, and 

 that this increase was still more marked in the case of 

 carbonic acid. 



According to Thermo-dynamics, this discrepancy sug- 

 g sted that there would be a similarly small cooling effect 

 when gas is forced through a small aperture and allowed to 

 come to rest. Joule had shown that this cooling was 

 insensibly small in his experiments on air ; but this was 

 quite consistent with the very small deviation from Boyles' 

 law discovered by Regnault, so that to find the cooling 

 effect it was necessary to make experiments more 

 dire::'v adapted to the elucidation of this point A 



