486 M. H. Weber on the Heat-conducting Power 



If, then, for a series of different values of 6 in the same period 

 we obtain by observation the temperature-differences D^ii oi* 

 I^2ju,+i belonging to these times, from these we get a series of 

 equations from which M and N or M' and N' can be eliminated ; 

 and therewith the quantity P is given. According to (5) a 

 second equation is hereby obtained between h and k, which, in 

 conjunction with equation (3), leads to the knowledge of h and k, 

 and therewith also to that of H and K*. 



Description of the Apparatus. 



The arrangements made use of in order to fulfil rigorously the 

 conditions presupposed in the theory were the following. The 

 heating and cooling of the ends of the bar were effected by alter- 

 nately conducting over the ends steam of about one atmosphere 

 tension and water at a certain temperature. The bringing of 

 steam or water took place through the four cocks, A, B, C, D 

 (Plate V. fig. 1). The cocks A and B served for bringing the 

 steam. Each of them had three small pipes attached, a,, jS, y, 

 which brought and carried away the steam. From two boilers, 

 in which the steam was generated, it was conducted through 

 pipes to the pipes a, whence, according to the position of the 

 cocks, it either entered through y into the pipes 5, and through 

 these was conducted over the ends of the bar M N, or passed 

 through the pipes (3 into other pipes, through which it issued 

 into the air. Thus, during the observations, two independent 

 currents of steam were contmuously kept up ; and by the arrange- 

 ment described steam could at any moment, by a suitable posi- 

 tion of the cock-plugs, be conducted to the ends of the bar. 

 Pig 2 is a horizontal section of the cocks A and B. The line jo 

 gives one, and the dotted line q the other normal position of the 

 plug. C and D are usually singlebored cocks: when they are 

 in one normal position, the pipes e and 8 are in communication; 

 when, on the contrary, they are in the second normal position, 

 the ])ipes e are shut ofi". The pipes e were connected with the 

 municipal waterworks. The small receivers (Hgs. 3 and 4), 

 finally, into which the ends of the bar were soldered, were ma- 

 nufactured of very thin sheet brass. On the inside of the upper 



* If not satisfied with the tii-st term of the above-mentioned series, we 

 might also take the second term into consideration. For this we have 



40knS/3 u, 



which would have to be added to the above expression for D2|a with plus, 

 and to the expression for D2,a + i with minus signs. Its value, however, in 

 the following observations does not amount to the mdhonth part of that 

 of the first term. 



