Mass-Spectra of Chemical Elements. 



615 



bolts into the arms of the magnet, and so form a structure 

 of great weight and rigidity and provide an admirable 



Current for the 

 arge accumulators. 



foundation for ihe whole apparatus 

 magnet is provided by a special set of 



The hydrogen lines are brought on to the plate at about 

 0*2 ampere, and an increase to 5 amperes, which gives 

 practical saturation, only just brings the singly-charged 

 mercury lines into view. The discharge is protected from 

 the strong field of the magnet by the usual soft iron plates, 

 not shown. 



The C 



amera. 



The main body of the camera N is made of stout brass tube 

 6'4 cm. diameter, shaped to fit on to the transverse tube 

 containing the pole-pieces. The construction of the plate- 

 holder is indicated by the side view in fig. 1 and an end-on 

 view in fig. 3. The rays after being magnetically deflected 



Fier. 3. 



pass between two vertical brass plates Z, Z about 3 mm. 

 apart, and finally reach the photographic plate through a 

 narrow slot 2 mm. wide, 11*8 cm. long, cut in the horizontal 

 metal plate X, X. The three brass plates forming a 

 T-shaped girder are adjusted and locked in position by 

 a set of three levelling-screws at each end ; the right-hand 

 upper one is omitted in fig. 3. The plates Z, Z serve to 

 protect the rays completely from any stray electric field, 

 even that caused by the photographic plate itself becoming 

 charged, until within a few millimetres of their point of 

 impact. 



The photographic plate W, which is a 2 cm. strip cut 



