THE LAWS OF CONDUCTION OF HEAT IN BAES. 



105 



bar was made, which came from a different manufactory, and was probably 

 inferior in quality.* 



116. Tracing an interpolating curve through the projected observations of 

 Cases I. and II., which run nearly parallel and at no great distance, at tem- 

 peratures superior to 40° and do not diverge even in the higher and more 

 hypothetical part of the diagram, and doing the same separately for Case III., we 



obtain the following numbers, purely as results of observation:— In the first 



F 



column of each division of Table XII., we have the ratio _ dv, which expresses 



dx 

 the conductivity in terms of the heat required to raise a cubic foot of iron by 

 one degree Centigrade. In the two following columns, we have the same reduced 

 to the usual standard of conductivity in French and English measures re- 

 spectively.f 



TABLE. XII. 



Temp. 



Cases I. and II. 



Case III. 





CONDUCTIVITY. 





CONDUCTIVITY. 



Cent. 



F 







F 

















"• = dv 



Units : Foot, 



Units : Centi- 



k = dv 



Units : Foot, 



Units : Centi- 





~ dx 



Minute and 



metre, Minute, 



~ dx 



Minute, 



metre, Minute, 







Cent. Deg. 



Cent. Deg. 





Cent. Deg. 



Cent. Deg. 







•01506 



•01337 



12-42 



•01117 



•00992 



• 9-21 



25 



•01391 



•01235 



11-48 



•01062 



•00943 



8-79 



50 



•01288 



•01144 



10-63 



•01014 



•00904 



8-37 



75 



•01205 



•01070 



9-94 



•00974 



•00865 



804 



100 



•01140 



•01012 



940 



•00940 



•00835 



7-76 



125 



•01088 



•00966 



898 



•00916 



•00813 



756 



150 



•01052 



•00934 



8-68 



•00895 



•00795 



7-38 



175 



•01018 



•00904 



8-39 



•00877 



•00779 



7-23 



200 



•00987 



00876 



814 



•00860 



•00764 



7-10 



225 



•00958 



•00851 



7-90 



•00844 



•00749 



696 



250 



•00930 



•00826 



767 



•00826 



•00736 



6-84 



275 



•00902 



•00801 



7-44 



00815 



•00724 



6-72 



117. The coincidence of the results in the second column with the results of 

 the provisional reduction in the case of the 1^-inch bar, made in 1852, and 

 printed at Art. 33, page 144, of the former part of this paper, is both striking 

 and satisfactory. For it shows, as I there anticipated (Art. 38), that the 

 method is, to a great extent, independent of the ordinary instrumental errors, 



* Dr Matthiesson in his Experiments on the Electric Conductivity of Iron (Phil. Trans., 1863), 

 has found nearly equally wide variations in different specimens. 



f If the numbers in the first column of each division of the Table be called A, then A x 888 

 will express the conductivity in water-measure for the foot, minute, and Cent, degree ; and A x 825 

 gives the numbers in the third column, where the centimetre is substituted for the foot. 



VOL. XXIV. PART I. 2 F 



