346 

 TABLE 1. 



App. a 



Diameter of the platinum wire 



Length „ „ „ „ 



Electric resistance at 0"C of the platinum wire 



Temperature-coefficient of IVo, i<o-ioo 



Conductivity of the platinum wire 



Diameter of the glass tube 



4 ^, where A = section of the platinum wire 



2ro 

 / 



«0-100 



2 R 



, Ay. 



App. b 



= 0.005246 cm 2ro =0.005246 cm 



/ 



= 11.843 



= 5 418712 



= 0.003888 



= 0.1649 



= 1.449 cm 



- 1.2039.10-6 I 4 



k =3.138 



Wa = 1.4481 il 



xo-m =0.003888 

 = 0.1649 



2 R = 1.449 cm 

 4^ =4.5437.10-8 



for L and S may be computed : 



L — 0.2388 . El. [ . and S 



/ . ti 



0.2388 .Eu. I 



1 



k . tic 



If the loss of lieat at the ends coidd be neglected, /> and .S would 

 represent the radial loss of heat per degree and per cm for the 

 long and for ihe short wire respectively (in a surrounding ofO°C.). 

 In that case L and ,S as well as the (puintily I) defined l)elow 

 would all be ecpial. 



Attending now to the differeiu-e in length of the two platinum 

 wires we may according to GoLDSCHMinr assume, that the heat given 

 off by this portion of the wire is not influenced by the heat con- 

 duction of the terminals. If D represents the loss of heat per unit 

 length of a wire of the same section in an infinite cylinder of the 

 same shape with a temperature-difference of one degree with the 

 outside at 0° C, and if the loss of heat may be taken proportional 

 to the tem|)erature difference, t^^ being the temperature-difference of 

 the uniformly heated wire with the surroundings, we have 



<z^ = 



\v—io-~( ly, — »'j 



and D=:^.2?>m{Ei-Eu).l 



a{W—xv,) " ^ ' ''' {l—k).t^ 



From the value of D the mean conductivity K on the way 

 which the heat follows between the wire and the wall may be cal- 

 culated according to the relation '). 



!>= _ '"^^ ^ (in 



In 



R 



+ ^ 



1) M. VON Smoluchow^ski. W. a. 64, (1898) p. 101. 



