( 116 ) 
The work done in displacing the meniscus up and down is easily cal- 
culated. For the only final change in the apparatus is the passage of 
mercury from b toa. The quantity of mercury passed can be calculated 
from the section of the capillary tube d, the distance m, — ms and 
the specific gravity of the mercury s. This quantity is M==ds(m,—mg), 
M being given in grams 
d in square centimetres 
and m, and mz in centimetres. Let the difference of level between 
a and b be centimetres, then the work done is A =nM gram- 
centimetres. 
The potential energy of the displaced mercury is transformed into 
heat, partially by means of electric currents, partially by mechanical 
friction. 
It merits attention that the amount A is not changed by changes 
in the resistance of the circuit G. An increase of the resistance 
causes retardation in the movement of the meniscus; the energy of 
mechanical friction is diminished, whereas that of electric currents 
is increased with the same amount. 
If the stop-cocks have only changed the first for the second 
position and the meniscus has moved from mj to m,, the energy of 
the heat produced is = '/ A; for the motion of the mercury in 
the capillary — viz. the cause of the mechanical friction and of 
the electric currents — is, while the meniscus returns from mg to 
m, in all phases perfectly equal — but of contrary direction — to 
the motion of the original displacement from mj to mg. 
Hence in first changing the position of the stop-cocks a 
quantity of energy must not have been transformed into heat, 
but must have accumulated as elastic tension in the meniscus. 
It is only in returning from m, to mj, that the meniscus delivers 
its energy. 
An analogous reasoning can be used if the meniscus is displaced 
by the sudden application of a constant P. D. between the poles of 
the capillary electrometer, the pressure in the capillary remaining 
unchanged. 
If the P. D. Z is applied by closing the key, see fig. 1, then there 
will be a temporary current in the circuit G. The work done by 
the current will be Q= # = dT Joules, if Z, i and T are, as 
usually, expressed in Volts, Ampéres and seconds. 
ll, Q is transformed into heat, whereas 1/, Q is accumulated in 
the meniscus as in a condensor in the form of an electric charge. 
If with circumstances as for the rest unchanged the applied P. D. — 
by opening of the key — is removed, the meniscus returns to 
