TRANSACTIONS . OF SECTION A. 635 



ing sphere S' will always pass through the corresponding node N', and it is clear 

 that whenever S i-eturns to its initial position S' will do so also. 



A possible description of a radio-active change may be based on the fact that 

 the type of contact of two spheres alters wlien the centre of inversion lies 

 witliin one sphere. 



In the diagrams 0,, Oj are the centres of inversion ; the second figure in each 

 case represents the effect of the first inversion, the third figure the effect of the 

 second inversion. In diagram I. fig. 3. the point of contact is no longer a 

 node, since the .spberes touch externally and are associated with oppositely 

 charged particles ; consequently the spheres are not required to remain in contact 

 and can separate. 



(Note. — The idea of attaching a physical meaning to the point of contact of 

 the spheres was not given in the original manuscript presented to the Association; 

 it was introduced later during the formation of an abstract.) 



2. Secondary Radiation. By Professor J. A. McClelland. 



3. The Scintillations of Zinc Sulphide. 

 By Professor E. Rutherford, F.R.S. 



4. A De-termination of the Rate of Evolution of Heat by Pitchblende. 



By Horace H. Poole. 



A spherical vacuum jacketed vessel with a narrow neck is filled with powdered 

 and carefully dried pitchblende. The neck is filled with cottonwool and rendered 

 watertight Avith sheet rubber, and the whole is buried in ice. The difference of 

 temperature between the layer of pitchblende in contact with the bottom of the 

 vessel and the ice is measured by a sensitive thermo-couple. After about a fort- 

 night this temperature becomes steady, when the heat leakage across the walls of 

 the vessel is equal to the heat generated by the pitchblende. Tliis leakage depends 

 solely on the vessel and on the difference of temperature between inner and outer 

 walls, which is measured by the thermo-couple. The thermal conductance of the 

 vessel is found by substituting water for the pitchblende and determining its rate 

 of cooling. Hence the heat leakage is known, and, knowing the amount of pitch- 

 blende present, the heat evolution per gram is found. 



The thermo-couple is calibrated by placing one junction in finely broken ice 

 and the other in a mixture of broken ice and water, which can be subjected to 

 a known pressure. The deflection caused by the resulting small change of 

 temperature is noted, and hence sensitiveness of cjuple is found. 



Using 560'7 grs. of pitchblende in an atmosphere of nitrogen, the temperature 

 finilly steadied at 0°'0092 C. As the thermal conductance of vessel is .5-8 calories 

 per hour per degree difference of temperature between inside and outside, this 

 corresponds to a heat leakage of 0'0.5.3 calorie per hour. Hence heat evolution 

 per gram of pitchblende is 0-000094 calorie per hour. This is about twice the 

 quantity estimated from the Icnown amount of radium present. 



5. The Grating Spectrum of Radium Emanation. By T. KoYDS, M.Sc. 



Using a concave grating of 1 metre radius, intended for faint spectra, it has 

 been possible to obtain more accurate measurements of the wave-lengths of the 

 more intense lines in the emanation spectrum. The grating has a width of 

 3-5 inches, containing 15,000 lines to the inch. The dispersion in the first order 

 amounts to 16'8 A.I . per millimetre. 



