

Radio-activity ami the Electron Tlieory. 41T> 



72 hours. As before, there was a strong impression over cell A and 

 none over cell B. The figures were : 



Opacity log. = 0'89; Opacity = 7 -71. 



These experiments indicate that the electrons from the radio-active 

 agent, chiefly actinium, partake of the properties of a fog or mist 

 of material particles, capable of diffusing away in the free air like 

 odoriferous particles, when not kept in by a thick metal screen. 



A further experiment was now tried with the same apparatus, the 

 agent a strongly active radium and barium bromide. This material 

 being self-luminous, a sheet of black paper was placed immediately 

 over it, so that nothing but emanations capable of passing through the 

 opaque paper would be subject to experiment. After 4 hours' expo- 

 sure in total darkness, the film was developed. A good circular patch 

 was obtained over cell A, and a faint diffused darkening showed over 

 the rest of the film, darker at the spot immediately over cell B, 

 fading away at the sides as the distance became greater. That this 

 action was due to the material in the open cell B, and not to general 

 fog over the plate, was seen by the clearness of the film where 

 covered by the lead, and where shadows were thrown by the lead 

 cylinder and pillar. 



Circles of the same diameter were drawn round the dark impression 

 over A, and round the darkest part of the impression over cell B. 

 Measurements were taken of different parts of the spaces enclosed in 

 these circles, and the mean of all these came out 



Circle over cell A Opacity log. = 0'53 ; Opacity = 3 -39. 

 Circle over cell B Opacity log. = 32 ; Opacity = 2 09. 



Katio B/A - 0'62 



The experiment was repeated with the addition of a sheet of 

 aluminium, 0'02 mm. thick, under the black paper, the electrons now 

 having to pass through both paper and metal before reaching the film. 

 The exposure was for 6 hours, and the appearance on development 

 was very similar to the last : a dark disc over the protected cell A, 

 and a diffused action over the other part of the film, except in the 

 shadow of the lead supports. Measurements as on the previous 

 occasion gave the following results : 



Circle over cell A Opacity log. = 0-78 ; Opacity = 6-03. 

 Circle over cell B Opacity log. = 0-48 ; Opacity = 3-02. 



Ratio B/A = 0-5. 



A third experiment was tried with the same apparatus, using only 

 the aluminium plate as a screen to cut off the luminous rays. The 

 appearance on development was similar to the others, and the measure- 

 ments of opacities were 



2 G 2 



