336 Intelligence and Miscellaneous Articles. 



RESISTANCE TO THE CONDUCTION OF HEAT. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



I am indebted to Professor Clausius of Zurich for having pointed 

 out an oversight in some tables of coefficients of resistance to the 

 conduction of heat which appeared some time ago in a work of 

 mine ■ On the Steam-engine and other Prime Movers.' Those 

 coefficients were computed from data given by M. Peclet ; but in 

 the computation the difference of the French and British units of 

 weight (the kilogramme and the pound) was neglected. I now beg 

 leave to send you the annexed Tables of the corrected values of those 

 coefficients. Their meaning will be best understood by the aid of 

 the following formula. 



Conceive two media, whose temperatures, in degrees of Fahren- 

 heit, are respectively T' (the higher), and T (the lower), to be sepa- 

 rated from each other by a layer of any given substance, whose 

 thickness, in inches, is denoted by x. 



Let q denote the number of British units of heat (degrees of Fahr- 

 enheit) in a pound avoirdupois of water transmitted from the hotter 

 to the colder medium, per square foot of surf ace, per hour . 



Then the resistance of the layer means the following quantity : — 



T'-T_ 1 



— — -P*+ A{1 + B(T ,_ T) |> 



the first term being the internal resistance, and the second the super- 

 ficial resistance. 



Values of the coefficient of internal resistance, p. 



Gold, Platinum, Silver '0016 



Copper, -0018 



Iron -0043 



Zinc, -0045 



Lead -0090 



Marble '0716 



Brick -1500 



Values of A. 



Water on both sides of the conducting layer. 8*8 



Water on one side, air on the other : — 



Polished metallic surfaces 0'90 



Dull metallic surfaces 1*58 



Glass and varnished surfaces 1*31 



Surfaces coated with lampblack . . .«, 1*74 



Values ofB. 

 Water on both sides of the conducting layer. 0*0580 

 Water on one side, air on the other : — 



Polished metallic surfaces 0'0028 



Rough and non-metallic surfaces. . . . - 0037 

 I am, Gentlemen, 



Your most obedient Servant, 

 Glasgow, March 17, 1862. W. J. Macquorn Rankine. 



