A Positive Ray Spectrograph. 707 



-eventually expressed in terms o£ electric charge or the move- 

 ment of charge. Resistance to compression is a repulsion 

 between the structural elements of matter possibly of the 

 nature of an electrostatic repulsion between electrons which 

 form the outer frame of atoms. The sudden compression of 

 a sound-wave then gives rise to electrostatic forces of recoil 

 and the velocity of sound is the rate of uniform transmission 

 of these through a loaded aether. On the other hand, the 

 heat energy of irregular motion may be considered as that 

 of alternating atomic currents attracting and repelling at 

 random and so transmitting the motion electromagnetically. 

 It is possible to extend this to a general consideration of 

 thermal conductivity in insulators as an electromagnetic 

 phenomenon. The object of the present note is to direct 

 attention to the above relations between k, E, p, and V 

 which must be explained by any theory of conduction in non- 

 metallic solids. The chief practical qualification of a material 

 -as a heat insulator is that it should be light and inelastic. 



LXXIV. A Positive Ray Spectrograph. By F. W. Aston, 

 M.A., D.Sc, Clerk Maxwell Student of the University of 

 Cambridge* . 



[Plate IX.1 



ff^HE analysis of positive rays by electric and magnetic 



JL fields giving deflexions at right angles to each other has 



been very completely worked out by Prof. Sir J. J. Thomson f. 



Alternative methods have been suggested by Dempster J and 



others. Dempster's arrangement depends on the knowledge 



of the potential through which the rays have fallen in the 



discharge-tube, and is therefore only practicable in the case 



of low velocity rays. 



Positive rays obtained from an ordinary discharge-bulb 



vary both in mass and velocity. An electric field will spread 



them into an 'electric spectrum' with deflexions proportional 



e 

 to — g.; a magnetic field will spread them into a ' magnetic 



spectrum ' with deflexions proportional to . In Thomson's 



method of crossed deflexions, in which both fields are applied 

 simultaneously, rays having constant — will lie on parabolas § 



* Communicated by the Author. 

 t ' Rays of Positive Electricity,' p. 7 et seq. 

 \ Phys. Review, vol. xi. p. 31G (1918). 

 .§ L. c. p. 12. 



