the Metals of the Alkalies and Alkaline Earths. 85 



the fastening in the wire-holders, we had 



L'i=-3-15, L"i = ll-55, 



from which we find 



a=59-4, &=47-5. 



For the experiments with calcium, strontium and magnesium, 

 another normal wire and other connecting wires were used ; here 

 we had therefore other values for n, a and b. 



When the resistance, w, is known in terms of our unit of re- 

 sistance, we can determine the ratio we require as follows : — Let 

 \ be its conducting power, L its length in millimetres, 8 its dia- 

 meter, r the diameter of the normal silver wire, and s the conduct- 

 ing power of silver at the temperature at the time the observation 

 was made, determined by a thermometer placed in the rock-oil 

 contained in the cylinder N; then 



Taking the conducting power of silver at 0° C. =100, then, 

 according to Lenz's formula*, it is at f C, 



s= 100-0-29354; + 0-0003776^^ 



L was determined after the observation had been made by 

 means of a beam- compass, S was found by measuring the fine 

 opening of the press under the microscope. Lead wires pressed 

 cold showed the same diameter as the opening of the press ; we 

 can therefore take it for granted that it was the same with po- 

 tassium, sodium and lithium wires ; with the hot-pressed wires, 

 calcium, strontium and magnesium, the diameter was measured 

 directly under the microscope whilst the wire lay m rock-oil : 

 here we found the diameter inconstant, and always smaller than 

 the opening of the press ; the mean of the diameters of the two 

 ends was therefore taken and brought into calculation. 



The results which were obtained with the different wires now 

 follow. In the first two columns arc the values of L, and L^, 

 of which the arithmetical mean was taken ; the third gives 

 the temperature t of the normal silver wire ; the fourth the tem- 

 perature T of the wire in the trough; the fifth the diameter 8 in 

 millimetres ; the sixth the length L, also in millimetres ; fm^l the 

 seventh the conducting power \ for the temperature T. ihe 

 values of 11, a, b, and r are also annexed. 



* Poggendorff' 8 Annalen, vol. xxxiv. p. 433. 



