RADIUM 



191 



smaller than the hydrogen atom. By means of the following experi- 

 ment the magnetic deviation of the /? rays ma}^ be demonstrated. A 

 tiny phial holding a little vadium, R, is placed at one end of a thick- 

 walled lead tube, AB, as shown in section in fig. 3. An electroscope 

 is placed somewhat bej^ond the other end of the tube, so that the pen- 

 cil of rays emerging from the tube tends to discharge the electroscope. 

 The lead tube is situated between the poles of an electro-magnet, E E, 

 and at right angles to the line of poles, N 8. When the current is 

 flowing in the coils of the electro-magnet the ft rays are thrown upon 

 the walls of the lead tube, and do not escape to discharge the electro- 



E G 



tar 



th 





3 



Etecfrometer 



m' 



TM 



A — A 



Fig. 4. — Ncfiativo electrical charges transporter! by /3 rays. 



scope as })efore, so that it now discharges more slowly. When the 

 current is cut oti' the electroscope is again rapidly discharged. 



It ma}' be shown that the ft rays transport negative electricity, which 

 is in harmony with the hypothesis that the}^ are electrically charged 

 projectiles.'^* For this experiment the apparatus illustrated in fig. 4 

 may ])c employed, in which R R represents the radium emitting the ft 

 rays. Those among them which are directed toward the upper part 

 of the figure traverse successively a thin sheet of aluminum, E E P] E, 

 in electrical contact with the earth, and supporting an insulating block 

 of parafiin, / / i /. They are finall}^ a])sorbed by a lead block, M M, 

 which is connected to an electrometer by an insidated wire. It is 

 E C 



l^rlh, 





Electrometef 



Fig. 5. — Negative charges carried by 8 rays. 



found that the electrometer is continually charged negatively. In 

 this experiment the ly rays are absorbed by the sheet of aluminum 

 which is connected to earth. The layer of paraffin is required to 

 insulate the lead block M M, foi* the insulation of this Itlock would be 

 defecti\e if there was oidy air between it and the aluminum, on account 

 of the air being rendered coiidncting by th<> presence of the rays, so 

 that it would then he impossible to (h'teet at th(^ electrometer the 

 charging of the lead block. 



An experiment the in\ crx' of this may be performed. The metallic 

 trough A A (fig. 5) containing radium. R, is connected with the elec- 



«M. :m.l :\Iim'. Cmif, C. IL, March h, 1900. 



