1020 
the values of the fourth column. These hood lie around Minrikan’s 
value 4.77 1010, 
I shall discuss the meaning of m in the following $§. 
9. I have stated in § 3 that I also observed the particle in an 
alternate field. It then executed a vibrating movement, and made 
the impression of a luminous line, clearest at the extremity where 
the velocity was smallest, so that as a whole it resembled a dumb- 
bell. Accordingly [ shall speak of the dumb-bell movement. I have 
tried to measure the length of this dumb-bell by comparing the 
falling luminous line witb the distance of the dividing lines. This 
was very difficult, particularly because I had only a few seconds 
time. Then the constant field had again to be excited by quick 
throwing over of a number of switches, so that I could make the 
particle rise again before it disappeared out of the field of vision. 
Hence the measurements are only estimations with a considerable 
mean error. I wanted to try and get an answer to the following 
question: does STOKEs-CUNNINGHAM's formula sufficiently express the 
resistance also for this rapid movement? 
Then the movement must satisfy the equation: 
ze t : 
BN SO 5 ae rare Te Ly UN le PR kernen oe CN 
€, is the maximum intensity of field, T the period of the alternate 
current'). It is easy to calculate that we find for the length of the 
dumb-bell from this equation: 
nen eE (TN: 1 
a M In ma K?T? 
1 
ai An? 
sGr 
in which K = -, 
M 
= er: . 
Now Kk — is large with respect to1, so that we may write: 
TT 
2A = e€ = 17 
7 ° 61°Gak LE 
In table III moor. gives the value of 2A calculated from equation 
(17) expressed in multiples of the distance of 2 lines; imeas, gives 
the measured lengths. It appears that mear. is always smaller than 
Meas» This suggests that the resistance for the vibrating movement 
') Only in approximation is the intensity of the alternate field represented by 
a sinus function. 
