146 PRINCIPAL FORBES ON THE CONDUCTION OF HEAT IN BARS, ETC. 



When the revision of the scales of the thermometers has been applied to the 

 results (which will necessitate the re-construction of the diagrams), I intend to 

 publish the final results for iron in a sequel to this paper. 



38. The following consideration, however, as it encouraged me to go through 

 the labour of the provisional calculation, makes me believe that the results will 

 not be materially altered. Indeed, it is one of the advantages of the method here 

 employed, to render us in some degree independent of the precision of the ther- 

 mometers. Since the same thermometers were carefully used in both the stati- 

 cal and dynamical experiments, the outstanding errors of temperature, as read 

 oj0f, will affect both results, if not exactly to the same amount, at all events in 

 the same direction. The final columns of the tables of page 144, containing the 

 conducting powers, depend on the ratio of two quantities — the flux of heat (F) 

 at any point, depending partly on the dynamical, partly on the statical experi- 



ment, and the differential co-eflBcient ^, depending wholly on the statical ex- 

 periment. The thermometric error will make both these quantities too great, or 

 else both too small, and the ratio will be but slightly affected. 



St Andrews, 21si April 1862. 



Postscript. 



The diminishing conducting power of iron with increased temperature har- 

 monises with similar facts in electricity, thus adding a fresh analogy to those 

 adverted, to in Art. 2 of the preceding paper. According to the recent experi- 

 ments of Arndtsen {Poggendorff's Annale% May 18.58), the resistance to the 

 transmission of electricity through iron is increased nearly one-half by a rise of 

 temperature of 100° Cent. 



28i/i A'pril 1862. 



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