Beta Rays and by Gamma Rays from Radium C. 555 



electroscope of which a disk and guard-ring formed an 

 integral part. This type of electroscope proved to have 

 great merits, and it may be found serviceable in other cases. 

 It is shown in fig. 2. There are three circular plates of 



FiR-. 2. 



MICA APRON 



aluminium about half a millimetre thick. The upper one is 

 supported by knitting - needles, around which pass the 

 cylindrical thin-walled sides, made of ordinary foolscap 

 paper, lined with very thin aluminium-foil. The knitting- 

 needles stand in ebonite posts, which support the other pair 

 of circular plates. The disk was cut from the middle 

 aluminium plate and suspended by a wire from an amber 

 bead in the top disk. The gold-leaf was fastened to the 

 middle of the wire. The disk was kept in place in the guard- 

 ring by three small ebonite bridges, glued at each end. The 

 lower aluminium plate was charged to a potential V, whilst 



