On some Problems of the Mass-Spectrogrqph. 515 



magnetic fields respectively. Then 



tan J^ = ^/R, 



and we know that, as the energy is constant, E, varies as 

 r^/m. We may therefore write 



tani0 = x /(m o /m). 



(i) 



where m Q (a constant) can be interpreted as that mass which 

 under the conditions of the experiment is bent through one 

 right angle in the magnetic field. Equation (1) expresses 

 in an exact and convenient form the same facts as equations 

 (1) and (2) of the first paper already cited. It is only 

 through m that the actual values of the fields affect the 

 mass-scale on the plate. 



Fiff. 1. 



But 



It appears from fig. 1 that 



NF = p cot ($-20) =p 



2 tan |0 



1 + tan $ tan 26 



tan cf> = 



tan cj> — tan 26 

 2y/(mm Q ) 

 m — m 



m — 2 s/ (mm ) tan 2 6 

 (m—nto) tan 26 



(2; 



l-tan 2 i</> 

 by (1). Hence 



NF_ m 

 p ~ 2 v /(mm ) 



N is of course a fixed point, which in the actual apparatus 

 is approximately 5*4 cm. behind the fiducial spot. When 

 m and the geometrical constants p and 6 are known, 

 equation (2) enables us to calculate thVposition of the image 

 on the plate for any desired mass. 



2 L 2 



