246 MM. Jamin and Richard on the Cooling of Gases. 



of the abscissae an angle the tangent of wbicii is equal to the expo- 

 nent d'; 



(2) That, for any constant values of the excess of pressure h, 



the values of log ( — ^-j are represented by the ordinates of a 



second system of parallel straight lines whose abscissae are log H, 

 and which make with the axis of the abscissae an angle the tan- 

 gent of which is equal to the exponent d'—d. 



We will indicate how" the verifications were made, taking hy- 

 drogen for example. 



Under pressures successively equal to 823"7 millims,, 689'7 

 millims, . . . , the value of h was observed every five seconds (as 

 was said before) ; then, on one and the same sheet of ruled paper, 

 the values of Ji were constructed, the time being taken for ab- 

 scissa — which gave as many curves as there were series of ob- 

 servations; and upon these curves the points having equal 

 ordinates h 200, 190, . . . , w^ere marked by horizontal lines. 

 These values of h are entered in the first column of the opposite 

 Table. The tangents were drawn to these several points, and 



the value of -7- obtained for each curve. They are placed in the 



columns marked A. 



(1) The values of — r- in each column A correspond to one 



and the same value of H and to different excesses of pressure ; 

 and if, taking log A for abscissae, we construct the line w^hose or- 

 dinates are log( — -^K it is found to be exactly a right line. 



On repeating the same construction the same result is found for 

 each of the pressures H. Moreover all these right lines are 

 parallel, and differ only by the ordinate at the origin ; they make 

 with the axis of the abscissae an angle the tangent of which is 

 =sl"2. The exponent d^ is therefore equal to this number. 



The columns No. 1 contain the values of 7- derived from the 



ax 



several right lines opposite the observed numbers of series A. 



The agreement is very satisfactory. 



(2)' The observed values of — -7-^ in any of the horizontal lines 



answer to equal values of the excess of pressure h and to different 



initial pressures H. The loo;arithms of — 4^ are constructed by 



^ ° ax -^ 



taking for abscissae the values of log H ; and as many outlines 

 are obtained as there are horizontal lines in the Table. We find 

 that they represent a second system of right lines^ all parallel, 



