Number of Electrons concerned in Metallic Conduction. 105 



in the position indicated by a. fine quartz fibre, the bulb B 

 being provided with a vertical tube (not shown) for carrying 

 the suspension. If we begin heating the residual air or 

 vapour in A, a puff will issue from the neck, and will turn 

 the vane C in azimuth, the deflexion being read through 

 the window D. A good notion of suitable dimensions can 

 be gained from Jordan's paper. Meanwhile it may be 

 mentioned that one of that author's galvanometers gave a 

 deflexion of 4 mm. at a scale-distance of 64 cm. for a steady 

 heating of one micro-watt suddenly commenced ; the maxi- 

 mum excursion being reached in about 2 seconds, after which 

 the vane gradually recovered its normal position. In this 

 case the air was at atmospheric pressure, and general con- 

 siderations seem to suggest that at lower pressure a greater 

 effect should be obtained for a like rate of heat-production, 



63. Suppose that, to begin with, the system contains air 

 at '01 mm. pressure*, free from mercury vapour. A beam 

 from the resonance-lamp is suddenly made to fall on A, and 

 if the vane executes a significant movement, the extent of 

 this is noted. (Probably the movement of the vane would 

 be very small, for in 2 seconds or so any slight absorption 

 by the silica walls would hardly have time to affect the 

 temperature of the contained air perceptibly.) A drop of 

 mercury is now introduced, and the test repeated ; in the 

 absence of true absorption the excursion of the vane should 

 be about the same as before. The apparatus would of course 

 need calibrating, if only roughly. Further details would be 

 out of place here, but I cannot help thinking that in some 

 such manner definite results might be obtained by a skilful 

 observer. 



Boar's Hill, Oxford, 

 3rd May, 191 5. 



VI. On the Number of Electrons concerned in Metallic 

 Conduction. By G. H. LlVENsf. 



THE mathematical theory of metallic conduction has been 

 extensively developed by various writers with a view 

 not only to placing the theory on as firm a foundation as 

 possible, but also with the object of determining more pre- 

 cisely the general electrical properties of the metals. The 

 results of certain forms of theory are certainly in fair agree- 

 ment with experiment, but the agreement obtained, even 



* This air-pressure is suggested because Wood lias found it to have 

 no perceptible influence on the absorption of 2o3tJ radiation by mercury- 

 vapour at room temperature. 



t Communicated bv the Author. 



