80 InteUi(/ence and MUcellaneou^ Articlfi^. 



Vol' llie luimoru-al c;ilculalioii, h and J must he known. "Bnf- J, 

 originally oxpivss.^d by resistanoo, eurrent-inkMisity, and condiict- 

 inp;-|)o\ver, can also be expressed by 7i and the sni-race-teinperature 

 allained; for i'roin tlie comparison of equations I. and 11. it fol- 

 lows that 97, 



J=±(r-U). 



a 

 I. (.letermined // by experiment thus : ihroii<;h a i iiick-walled brass 

 tube 1 caused hot water of a known temperature to tlow, and ob- 

 served the ti^mperature on the outer surface of the mantle. Theory 

 gives for this case 



h=^ ^2-^1 



^'iC-, - U") (log nat c, — log nat cj 

 in which r, and r, denote the temperatures, (\ and c^ the radii, of 

 the outer and inner circumferences ; and then the result of the 

 observations is /, =0-00078. 



I'or a brass \Aire it can now be calculated how much the tempe- 

 ra' in'o at the centre is higher than that at the surface; and ^hen 

 a = 0-2o millim., 7- = 55^-5 C, U= 18° C, we get 



AVithout making further observations, tlu^ temperature-diirerence 

 can now be calculated for other wires also. 



In conclusion, 1 must not omit to mention that Edlund, in the 

 IMay Number of Poggendorff's Aanalen, has also gi\en a calcula- 

 tion of the distribution of temperature in a galvanically heated wire; 

 his deduction, however, proceeds quite dilferently from that here 

 given ; tiie equations obtained are not so general, and the numerical 

 dtita are based on experimen's of anotlu^r kind than those 1 have 

 employed; so that 1 had no hesitation in making public my inves- 

 tigations, which were ready before the appearance of Ediund's 

 memoir. — yiiisziu/ aus; dcm am 12. Auc/. 1870 dt'r licJactlon von 

 1\>J[I. Ann. (/. P/i)i.<. ((. Chi'inle eingesandten Mana^cripte. 



ON THK STECIFIC HEATS OF GASES. 



To the Editors of the r]tUosoj}iucal Matjazlne and Joarnal, 



Gentle Ml ;n, 



Mr. Burbury has pointed out to me a mistake in my ]niper on 



dissociation in the June number of the Philosophical Magazine 



A\ hich is iujportant. On page 415, the sign of 1 should be cluingcd. 



^J'his will aifect the ratio of the specific heats given on p. 417; in 



the first ease — will be 1*585 instead of 1'609, and in the second 



(' 

 l-'S-^S instead of 1'423. Consequently tlse reasoning at the end of 

 § 20, which de])ends on these ratios, will be invalidated. If the 

 quantity 1 were positive, as in the paper, \\e should get gases cooling 

 ^^ hen they combine, or passing from one state into a less stable state. 

 1 am, Gentlemen, 



Yours truly, 



AV. M. Hicks. 



