266 Pi'of. Thomson, A Method of Comparing the [Feb. 11, 



and size filled with the different electrolytes were placed in the 

 coil, and the effect they produced on the exhausted bulb in coil B 

 Fig. (2) compared. In these experiments the electrolytes are 

 exposed to electromotive forces of exceedingly high frequency, the 

 frequency being that of the electrical oscillations produced by the 

 discharge of the jar ; this was more than a million per second. 

 The electromotive forces while they last are exceedingly intense, 

 so that the circumstances under which the electrolyte is placed in 

 these experiments are very different from those which obtain in 

 the ordinary determinations of the resistance of electrolytes. 

 I found however, as in my previous experiments on this point 

 made by a different method (Proc. Roy. Soc. Vol. XLV. p. 269 

 (1889)), that the proportion between the resistances determined 

 in this way was the same as for steady currents. A point I 

 specially investigated was to see whether solutions of sulphuric 

 acid showed the same peculiarities in the relation between the 

 conductivity and the strength of solution as are found when the 

 conductivities are measured under steady currents. 1 found, 

 starting with pure water and gradually adding sulphuric acid, 

 that at first each fresh addition of acid produced an increase in 

 the conductivity, this went on until the solution contained about 

 157o hy volume of H^SO^, at this point the addition of acid 

 produced too small an effect to be appreciable by this method ; 

 the conductivity did not seem to change much until the solution 

 contained about 60°/^ by volume of HgSO^ ; at this point the 

 addition of fresh acid produced an appreciable diminution in the 

 conductivity of the solution, and this diminution went on as the 

 strength of the solution was increased. Thus except that the 

 method is not sufficiently delicate to detect the small differences 

 of conductivity with the strength of the solution which occur in 

 the neighbourhood of the state of maximum conductivity, the 

 results obtained by this method agree exactly with those obtained 

 with steady currents. 



The agreement of resistances obtained by using small electro- 

 motive forces with those obtained by this method when large 

 electromotive forces are used is interesting inasmuch as it shows 

 that these large electromotive forces do not appreciably increase 

 the amount of dissociation of the electrolyte. 



Conductivity of Flames. This is very easily shown by means 

 of this apparatus. All that is necessary is to place in A an 

 ordinary lamp-glass. When the flame from a Bunsen burner 

 is placed under this a very marked diminution in the luminosity 

 of the bulb in B is produced. 



Variation of the Conductivity of a Gas with the Pressure. This 

 was determined by comparing the effect produced by a bulb filled 



