128 =D. Boboulieff— Dissipation of Electricity in Gases. 
bar which supported the needle was in the magnetic meridian. 
When the balls are each charged with the same quantity of 
electricity, the bar MN will deviate by the angle aj; then the 
moment of the repulsion of the electrical forces may be ex- 
pressed thus: 
Q? 
rire eee od: 
and the moment of the magnetic force, 
MT sin a,, 
where L is the half length of the bar; 
M the magnetic moment of the needle 
mn, and 'T' the intensity of terrestrial 
magnetism. ithe both expres- 
sions we 0 
(5) a 8MTL sin’® $a,. 
After the lapse of the time ¢, the 
quantity of electricity will become Q, 
and the angle of deviation will be a: 
(6) Q’ = 8MTL sin® 4a. 
Eliminating the ——<. Q and Q, from the equations (1), 
(5) and (6), we obta 
(7) Bae 3(log sin $a,—log sin $a) 
According to this formula I have computed p. 
I am certain that each time 1 read the divisions on the paper 
scale BB, I could not make an error greater than one-half of a 
degree. The angle a ora is the mean of four observed num- 
bers ; if in the neutral state of the balls I read the divisions X 
and x and when they were electrified, the divisions Y an 
a then a is equal the half sum of the ‘diff fferences X—Y and 
In each of these four readings I could not commit an 
error of one-half of a degree; pera eas the largest error in 
the determination of the angles “and —* could amount only 
Tf $a and 4ay be varied +80’, then the log sin $a, and log sin 
ga will vary, which I indicate thus 
A log sin $a, and A Se sin 4a; 
as a consequence of this, p will change to 4p; and we have 
