350 Dr. Barnes and Mr. Mcintosh on a New 



potential-differences for the different pairs of metals are as 



follows : — 



Difference of Potential, 

 (millivolts). 

 Aluminiums ^_ 



Zinc 35 



Lead *-^ 



Tin 37 



Copper ) 306 



values which are considerably below those generally adopted. 



Conclitsions. 



The gas between the two cylinders always contains a 

 number of ions, and, on account of the greater rate of diffusion 

 of the negative ions, it is possible that an excess of these 

 would impingQ upon the inner cylinder in a given time, and 

 thus leave it negatively charged. The resulting potential, 

 however, should be the same for all metals on this hypothesis. 



Again, it is possible that the very penetrating radiation 

 which is present in ordinary air may consist of negatively 

 charged matter, and that the negative charge taken up by the 

 inner cylinder represents the amount of this radiation inter- 

 cepted by it. But the high value obtained for aluminium, 

 together with the results obtained with Rontgen rays, is 

 against this conclusion. 



It seems rather that a process is going on at the surface of 

 the metal, whereby an excess of positively charged corpuscles 

 is being continually emitted, and that the steady state 

 attained represents a condition of equilibrium in which the 

 current between the cylinders is equal to the rate of efflux of 

 the positive charges. 



XLIII. A Neic Form of Platinum Re si stance- T1iermomete7\ 

 specially adapted j or the Continuous-flow Calorimeter. By 

 H. T. Baknes, D.Sc, Assistant Professor of Physics, and 

 D. MoIntosh, M.A., Demonstrator in Chemistry, McGill 

 University *. 



ONE of the difficulties to be overcome in constructing a 

 sensitive platinum thermometer is to restrict the size of 

 the coil of wire forming the bulb. In order to have a suflScient 

 length of wire it is often necessary to make the bulb incon- 

 veniently large, and thereby sacrifice quickness of register. 



The form of thermometer which we have devised meets 

 this difficultv to a considerable extent, and has enabled us to 

 use shorter bulbs. 



* Communicated by Prof. H. L. Callendar, F.E.S. 



