540 Intelligence and Miscellaneous Articles. 
nicates with the ground, the excited charge of the external cylinder 
is equal to the evetling charge of the internal cylinder. 
2. When the external cylinder is the collector, the excited charge 
of the internal cylinder is precisely the same as it would have been 
if it had been put in direct communication with the same source. 
3. When the external cylinder is the collector, its charge may be 
considered as consisting of two parts, one of which is equal to the 
excited charge of the internal cylinder, the other representing the 
quantity of electricity which the external cylinder would take up by 
itself under the influence only of the medium in which it is placed. 
The latter law enables us to foresee what would happen in the case 
of a condenser formed of three concentric cylinders, The charge 
which the middle cylinder would take up when put in commu. 
nication with the source, the other two being connected with the 
ground, must be equal to the charge which would be excited in it by 
the two other cylinders. I have found by experiment that this is 
really the case. 
It follows that condensers arranged in a spiral form, may serve to 
collect in a small volume a large quantity of electricity. 
4. If we agree to call by the name of resistance to excitation a 
quantity inversely proportional to the charge received by either 
armature, when the tension of the internal cylinder is maintained 
at unity, and that of the external cylinder at zero, then this resist- 
ance, which I shall call p, is expressed by the formula 
p=hk log Ro 
- 
R and r representing the respective radii of the external and internal 
cylinders, and k being a constant which depends on the inductive 
capacity of the dielectric, and on the length of the cylinder em- 
ployed. 
This formula is remarkable, since it might have been deduced 4 
priori from the ordinary theory of propagation by conductibility. 
Suppose, in fact, that the substance which separates the two cylin- 
drical armatures of the condensers possesses a certain conductibility, 
and Jet us call by the name of resistance to conduciibility, a quantity 
inversely proportional to the amount of clectricity which, in a unit 
of time, traverses the annular space between the two cylinders, the 
tension of the internal cylinder being maintained at unity, that of 
the external cylinder at nothing. ‘This resistance to conductibility 
may be caleulated according to the principles established by Ohm, 
and it will be found that it is expressed by the same formula as the 
resistance to excitation, ‘To pass from one formula to the other, it is 
only necessary to change the meaning of k. We may say therefore 
that the same theory, that namely of Ohm, regulates propagation by 
excitation and propagation by conductibility, at least when we con- 
fine ourselves to the consideration of spaces bounded by concentric 
cylinders. I propose to verify this principle under other circum- 
stances, and especially in the case of spherical condensers.— Comptes 
Rendus, Feb. 18th, 1861. 
