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VIII. — Experimental Inquiry into the Laws of the Conduction of Heat in Bars. 

 Part II. On the Conductivity of Wrought Iron, deduced from the Experiments 

 of 1851. By James D. Forbes, D.C.L., LL.D., F.R.S., V.P.R.S. Ed., Principal 

 of St Salvator and St Leonard's College, St Andrews, and Corresp. Member 

 of the Institute of France. (Plates I., II., III., IV., and V.) 



(Read 20th February 1865.) 



CONTENTS. 



Introduction, 



§ I. Statical Experiments — Graphical Interpola 

 tions — Equations to Statical Curves, 



§ II. Experiments on Cooling — Graphical Inter 

 polations — Equations, . 



§ III* On the Proportion of Heat dissipated by- 

 Radiation and by Convection, 



§ IV. The " Statical Curve of Cooling"— Reca- 



Page 



73 



75 



87 



95 



pitulation and Application of the Method 

 of deducing the Conductivity, 



§ V. The Method of this Paper applied, under 

 the usual assumptions of the Theory of 

 Conduction, as a first approximation to 

 the determination of Conductivity, 



§ VI. Final determination of the Conductivity 

 of Iron at various Temperatures, . 



§ VII* Concluding Remarks and Suggestions, 



Page 



97 



99 



101 

 106 



INTEODUCTIOK 



The Articles are numbered in continuation of those in the First Part of this Paper. 



39. In the first part of this paper, read to the Royal Society of Edinburgh in 

 April 1862, and published in their Transactions,! I explained the principles of a 

 method devised by me in 1850 for ascertaining the absolute conducting power of 

 substances capable of being formed into long bars ; and I also stated the general 

 results of experiments made in 1851 on the Conductivity for heat of wrought 

 Iron. 



40. I explained in Art. 14 of that paper, that the publication of the results 

 had been for ten years withheld, partly in consequence of the state of my health 

 which completely interrupted the experiments, but still more from the defective 

 graduation of some of the thermometers used, which made it necessary to submit 

 the instruments to a careful scrutiny, and to repeat with the duly corrected 

 numbers the whole of the elaborate projections of the curves and calculations 

 from them, on which the accuracy of the final results of course depends. 



41. I stated that the friendly aid and exemplary patience of the late Mr 

 Welsh of the Kew Observatory had supplied me with data for correcting the 

 readings of the most important, and at the same time the most inaccurately 

 graduated of the series of French thermometers employed in these experiments. 



* Sections III. and VII. have been added to this paper since it was read. 

 f Vol. XXIII. p. 133. 



VOL. XXIV. PART I. X 



