390 On a Wehnelt Cathode-Ray Tube Magnetometer. 



V. Tlie Results. 



Measurements were made on seven photographic plates, 

 numbered 27-34, number 29 being unexposed, for the 

 platinum strip was accidentally burned out while the 

 heating current was adjusted. Photographs 28, 30, 33, 

 with number 26, are shown in Plate VIII., and the data from 

 the measured photographs are collected in Table I. 



Table I. 



Plate 

 No. 



M. 



cm. 



I 

 aunperes. 



Ze 

 cm. 



Zee 

 cm. 



1-886 



Zee — Ze 

 cm. 



0-827 



H 



C.g.8. 



0-1590 



+0-0007 



27 



48-61 



33-13 



1-402 



1059 



28 



48-61 



33-13 



1-463 



0993 



1-812 



0-819 



01571 



-0-0012 



30 



48-61 



33-13 



1-432 



1-024 



1-863 



0839 



0-1548 



-0-0035 



31 



48 61 



33-13 



1-423 



1032 



1-846 



0-814 



0-1598 



+0-0015 



32 



48-61 



33-13 



1-417 



0-980 



1-759 



0-779 



01579 



-00004 



33 



48-61 



33-13 



1-323 



0952 



1-652 



0700 



0-1594 



+0-0011 



34 



4861 



3313 



1-473 



1-009 



1-831 



0-822 



0-1602 

 0-1583 



+0-0019 

 ±0-0005 



The constant M was calculated by the formula of the 

 preceding section, and agrees satisfactorily with the value 

 determined graphically. The diameter of the coil, the 

 distance between the cathode and the photographic plate 

 and the vertical distance of the latter from the edge of the 

 coil, were measured with a cathetometer, and it was deduced 

 that a = 43*46 cm., ^ = 33 13 cm., and ?' = 5*01 cm. It will 

 be remembered that the coil has six turns. 



The current was measured with a Siemens & Halske pre- 

 cision ammeter, removed from the magnetometer, to 1 part 

 in 1500, with no observed fluctuations during the time of 

 exposure. The deflexions tabulated are the half means 

 of live measurements of the distances between the outer two 

 and the inner two spots on each plate. The precision 

 attained in measuring deflexions is indicated by taking 

 Plate no. 33 as an example, where the maximum devia- 

 tion of a single measurement of z e from the mean of five 

 measurements is 1 part in 316, and for z ee it is 1 part in 235. 



The deviations from the mean of the values of H are tabu- 

 lated and the relative probable error of +0 00046 or qtt H 

 calculated, but the performance of the instrument is not 



