454 Dr. F. W. Aston on the 



typical case, the position occupied by carbon with a field of: 

 320 volts should be exactly coincident with the position 

 occupied by oxygen with 240 volts when the magnetic field 

 is constant. Over the range of fields used in the case of 

 neon, all such coincidences when expected have been found 

 to occur within the error of experiment whatever the position 

 on the pJate. 



For some reason, by no means obvious, connected with 

 the geometry of the apparatus the relation between displace- 

 ment and mass is very nearly linear, a fact which lightens 

 the labour and increases the accuracy of calibration very 

 considerably. 



Numerical results. 



In the case of plate B the masses of the neon lines were 

 estimated by carefully drawing the calibration curve repre- 

 senting the relation between displacement and mass by 

 means of the known lines 12, 13, 14, 15, 16 checked by that 

 at 28. 



With plate D another mode of procedure was adopted. 

 A linear relation was assumed and a table of corrections 

 made by means of reference lines, which correction when 

 subtracted from the observed displacement gave an exactly 

 linear relation with mass. A correction-curve (apparently 

 parabolic) was drawn, from which the appropriate corrections 

 for any displacements could be written down and the masses 

 corresponding to those displacements obtained by simple 

 proportion. The following table gives the results : — 





Table II. 









Plate B 









(Ne a ) + +. 



(Ne*) ++ , i 



:*NeV. 



(XeV- 





9-98 



11-00 



2000 



20-00 





10-02 



10-99 



19-95 

 19-97(5) 



22-01 





10-00 



10-99(5) 



22 00(5) 







Plate D 









10-01 



1106 



20-00 



21-90 





9-98 



10-98 



19-98 



22-10 





9-98 



11-01 



2000 



22-03 





— 



11-01 



19-90 



21-98 





9-99 



19-97 



22-00(5) 





method 



of measurement 



combined 



with a 



slight 



The 

 halation of the plate tends to make the edge of bright lines 

 appear a little too near the register spot, This is enough to 

 account for the reading of the very bright Ne 4 " line giving a 



