MM. Jamin and ^icha^rd on the Laws of Cooling. 459 



and h vary at the same time. They both vary equally if we 

 change the initial pressure H. We may make abstraction of the 

 current (which is here only a means for producing the heat), and 

 say that 7*'— r is a function of H and of h which it is the question 

 to determine. 



For this purpose several series of observations were made 

 under different initial pressures H (for example 814 millims., 

 788 millims., . . . 73*9 millims.); and in each case the number 

 of elements of the pile was varied from 5 to 20, which gave as 

 many pairs of values of h and r' — r as there were observations. 

 Taking one of these series (for example, that upon hydrogen 

 under the pressure of 788*4 millims.), and constructing the 

 series of points which have for abscissse log h, and for ordinates 

 log (r'—r), the tracing shows immediately that all these points 

 arrange themselves in a very regular straight line which makes 

 with the axis of the abscissse an angle whose tangent is 1*02; 

 its equation is 



log(r'-r) = logA+l-02log/i (2) 



If we now pass from this series to those corresponding to 

 other pressures, from 814*5 millims. to 73*9 millims,, we find 

 in each case a right line parallel to the preceding ; they all make 

 with the axis of the abscissse an angle whose tangent is 1*02. 

 These results are recorded in the following Table, which gives a 

 summary of a portion of the experiments we have made upon 

 hydrogen. The accordance between calculation and experiment 

 is rigorously maintained. 



Cooling of the wire in hydrogen. 

 (^=1-17; c = 0-37; n = 0-000267.) 



H = 814-5. 



H = 788-4. 



H = 656-2. 



H=587-7. 



H = 543-2. 





r' — r. 





r' — r. 





r' — r. 





r' — r. 





r'—r. 



h 





h 





h 





Ji 





h 







Obs. 



Calc. 



Obs. 



Calc. 





Obs. 



Calc. 





Obs. 



Cale. 





Obs. 



Calc. 



222 



1920 



1865 



217 184718621196 



1921 



1921 



180 



1941 



1908 



1.92 2344 



2389 



u;i 



1352 



1060 



156 1346 1341 



m 



1244 



1229 



122 



1271 



1271 



138 



1729 



1704 



100 1 817 



817 



102- f8l 869 



74 



683 



693 



70 



685 



710 



93 



1132 



1134 



33 256 



260 



32 255 261 



29 



225 



263 



27 



244 



263 



49 



610 



590 



H = 481-3. 



H = 407-3. 



H =313-2. 



H = 182-3. 



H = 73- 



9. 



176 



2408 



2363 



164 



2509 



2538 



140 



2617 



2617 



99 



2931 



2962 



59 3588 



3805 



133 



1794 



1774 



122 



1859 



1873 



104 



19o2 



1934 



72 



2108 



2145 



42 2729|2718| 



91 



1171 



1197 



80 



1225 



1220 



70 



1294 



1281 



49 



1528 



1447 



29 



1852|1852 



50 



631 



640 



44 



673 



661 



40 



718 



718 



29 



825 



832 



11 



1224 „ 



