126 Hon. E. J. Strutt. On the Conductivity of 



III. " The Anatomy of Symmetrical Double Monstrosities in the 



Trout." By Dr. J. F. Gemmill. Communicated by Pro- 

 fessor Cleland, F.E.S. 



IV. " Preliminary Communication on the (Estrous Cycle and the 



Formation of the Corpus Luteum in the Sheep." By F. H. A. 

 Marshall. Communicated by Professor J. C. Ewart, F.E.S. 



V, "On the Composition and Variations of the Pelvic Plexus in 

 Acanthias vulgaris." By E. C. Punnett. Communicated by 

 Dr. Gadow, F.ES. 



VI. " On the Heat dissipated by a Platinum Surface at High Tempera- 

 tures. IV. — High-Pressure Gases." By J. E. Petavel. 

 Communicated by Professor Schuster, F.E.S. 



" On the Conductivity of Gases under the Becquerel Bays." By 

 the Hon. E. J. Strutt, Fellow of Trinity College, Cambridge. 

 Communicated by Lord Eayleigh, F.E.S. Keceived De- 

 cember 15, 1900,— Eead February 21, 1901. 



(Abstract ) 



This paper gives an account of experiments on the relative con- 

 ductivities of gases under the action of Becquerel radiation from 

 various radio-active bodies. 



It is first explained that in order to determine the constants 

 fundamentally involved, the following conditions must be complied 

 with : — 



(1.) The E.M.F. applied to the conducting gas must be great enough 

 to consume all the ions produced by the rays. 



(2.) The pressure of the gas must be low enough to prevent any 

 appreciable fraction of the radiation being absorbed by it. 



If this is not so, then the layers of gas nearer the radio-active 

 surface are exposed to stronger radiation than those further from it. 

 The effective strength of the radiation will thus depend on the absorb- 

 ing power of the gas at the particular pressure, and the observed 

 ratio of the conductivities of two gases at the same pressure will not 

 represent the ratio of their conductivities under radiation of a given 

 strength. 



The criterion applied to test whether the absorption was appreciable, 

 was to examine the conductivity at different pressures. The range 

 was ascertained within which the law of approximate proportionality 

 to the pressure held good. In the experiments, care was taken to keep 

 the pressure well within that range. 



