﻿258 Magnetic Deflexion of Recoil Stream from Radium A. 



of its faintness. This difficulty was overcome by arranging 

 that the fiducial line should cover only one half o£ the 

 length o£ the image. Some bias in making the settings 

 was inevitable, and it seemed impossible to increase the 

 accuracv of the readings bevond a certain limit by multi- 

 plying observations. This was due to a tendency to adjust 

 the fiducial line on marks and dust spots which though faint 

 occurred on the plates. We eliminated this as far as possible 

 by inverting the photographic plate at intervals, thereby 

 changing its appearance in this respect, and by using the 

 independent measurements of three observers. Throughout 

 we have assumed that the densest part of the image in the 

 case of the recoil lines was the centre. The magnification used 

 was controlled by the intensity of the recoil lines; the greater 

 their density, the greater was the magnification that could be 

 employed. Although the recoil lines were distinctly visible 

 to the naked eye on each plate taken, yet only about half the 

 plates could be used for making accurate measurements. 



The measurements were made in sets of ten and the plate 

 was always readjusted between each set, so as to use dif- 

 ferent parts of the divided scale of the travelling telescope. 

 About six sets were taken on each plate. The final values 

 of the ratio d r /d a for each plate given in the table are the 

 means of all the observations. The vernier readings were 

 taken to the nearest hundredth of a millimetre, but the 

 means were worked out to the next significant figure. The 

 results of the measurements on several plates are given in the 

 following table, an inspection of which shows that the radius 

 of curvature of the recoil stream in a magnetic field is 

 double that of the a. rays with a high degree of accuracy. 



Table. 



No. of 

 plate. 



Approximate 

 field in gauss. 



h 



in cm. 



l, 2 . 

 in cm. 





pa _ 

 pr 



1 



13700 

 14500 

 15000 

 14600 

 15000 



3-5 

 S-5 

 3-5 

 3-5 

 3-5 



1-84 

 2-85 

 1-84 

 2-85 

 1-84 



0-4934 

 04977 

 0-4981 

 0-4967 

 0-5006 



Mean . . . 



0-4959 \ 



0-5017 



05008 



0-5006 



0-5055 



0-5009 



2 





4 



5 





We are^ greatiy indebted to Mr. N. Tunstall for his 

 assistance in measuring the plates. With his valuable help 

 we have been able to increase the accuracy of the experi- 

 ment by using the results of three independent observers. 



