Intelligence and Miscellaneous Articles. 449 



For this purpose a thermoelement was used consisting of very- 

 thin German silver and iron wire soldered together ; these wires 

 loaded with a small weight were so laid above the horizontal bar 

 that the junction was uppermost. At a distance of about 10 cm. 

 from this place both wires were soldered to thin copper wires, 

 which by means of a commutator were in connexion with a reflecting- 

 galvanometer. When the thermoelement was in contact with the 

 bars, the temperature of the junction was obviously proportional to 

 that of the section in question. 



Loss of heat by radiation was prevented by screens and coatings 

 of wadding. The junction at the copper wires was sufficiently near 

 to the temperature of the air for ray purposes. As the element 

 showed accidentally an electrical force nearly proportional to the 

 difference of temperature, the deflection of the galvanometer was 

 put for the difference of temperature. 



In order to get an approximate statement as to the absolute con- 

 ductivity, the loss of heat to the surroundings was measured by- 

 heating the enlire bar and then observing its gradual decrease of 

 temperature with the thermoelement suspended over it. These 

 observations were made by Mr. Sheldon. According to this the 

 temperature decreased in ten minutes in the ratio 1-67 : 3 ; the 

 external conductivity for temperature in one second is therefore 

 1-67/600-1 = 0-00086. 



This number multiplied by the specific heat 0-117 *, and the 

 density 7'9, gives the external thermal conductivity reduced to 

 unit section =0-00080, so that, denoting the internal conductivity 

 by Tc, we have 



dht 0-00080 



z= U. 



doe 2 Jc 



Considering now the temperatures u v u 2 , u 3 of three sections 

 distant from each other by the length I, putting 



the conductivity 



2u 2 

 Jc is known to be 



- 0-0008 f l T. 





Llognat(>+ Vw 2 -l)J 

 We obtain : — 

 for I = 4 5 8 

 fchard = 0-063 0-062 0-061 

 Tc soft = 0-106 0-118 

 Hence in the mean, 



Tc hard = 0*062 grm. cal./crn. sec. 



8 cm. 

 0-062 

 0-111 



Tc soft = 0-111 „ 

 The conductivity of soft steel is thus almost 80 per cent, greater than 



* According to Regnault, who puts the specific heat of hard steel at 

 one per cent, higher, and the density by as much lower than with soft 

 steel— Pogg. Ann. vol. lxxii. p. 73 (1877). 



