398 M. G. Wiedemaun on the Transmission of Heat in Metals, 



but 265 millims. long, were ground plane at one end. These 

 bars were then ])laced in a wooden frame with their polished ends 

 free, &c., and the arrangement made, that to the plane end of 

 each of the longer bars the plane end of one of the shorter was 

 firmly screwed. At a distance of 2 millims. from the place of 

 contact, and thence at distances of 21 "4 millims., holes of 

 0'9 millim. wide and 8 millims. deep were bored. These holes 

 were filled with oil. The end of each shorter bar was sur- 

 rounded by a tin case, through which steam was passed for a 

 long time. A screen protected the rest of the apparatus from 

 the rays of heat. The whole apparatus was placed in a tin vessel 

 surrounded by water, so that the loss of heat during the experi- 

 ment should be as uniform as possible. After the apparatus 

 had been constantly heated for two or three hours, and the heat 

 in the joined bars had become constant, the temperatures were 

 determined by sinking the thermo-electric element in the holes. 

 The thermo-electric element was needle-formed, and consisted 

 of two wires of iron and germau silver, 0'3 millim. thick., placed 

 together, but only soldered just at the end where they dipped in 

 the holes. At the other ends copper wires were soldered, 

 which communicated with the spirals of the galvanometer de- 

 scribed in an earlier treatise*. The whole of the thermo- 

 electric element, with the exception of the points dipping in the 

 holes, was fastened in a glass tube with sealing-wax, which was 

 cemented in a vessel of water in order to keep the posterior ends 

 of the element at a constant temperature. 



The following are some of the results obtained with the appa- 

 ratus. Under x the series of holes is given, beginning with that 

 nearest the place of junction. The holes corresponding to the 

 warmer bars, which are first in the list, are marked with +, 

 and the colder with — . Under / stand the con-esponding tem- 

 peratures. Each series contains the mean of several successive 

 observations. 



Poggendorflf's Annalen, vol. Ixxxix. p. 504. 



