He also discovered that a body charged with positive or negative electricity **repels** a body free to move when the latter is charged with electricity of like sign, but attracts it if it is charged with electricity of opposite sign, i.e.

Positive **repels** positive and negative **repels** negative, but positive attracts negative.

This he **repels**, and his answer may be summed up as follows.

A very small sphere is said then to possess a charge of one electrostatic unit of quantity, when it **repels** another similar and similarly electrified body with a force of one dyne, the centres being at a distance of one centimetre, provided that the spheres are in vacuo or immersed in some insulator, the dielectric constant of which is' taken as unity.

The explanation is as follows: the charge (-}- Q) of positive electricity on the ball creates by induction an equal charge (- Q) on the inside of the canister when placed in it, and **repels** to the exterior surface of the canister an equal charge (+ Q).

Having a charge Q **repels** a unit charge placed at a distance x from its centre with a force Q/x 2 dynes, and therefore the work W in ergs expended in bringing the unit up to that point from an infinite distance is given by the integral W = Q x 2 dx = Hence the potential at the surface of the sphere, and therefore the potential of the sphere, is Q/R, where R is the radius of the sphere in centimetres.

Baron Cuvier in his Eloge historique of Fourcroy **repels** the charge, but he can scarcely be acquitted of time-serving indifference, if indeed active, though secret, participation be not proved against him.

His eloquence was of the vehement order; but it wins hearers and readers by the strength of its passion, the energy of its truth, the pregnancy and elegance of its expression, just as much as it **repels** them by its heat without light, its sophistical argumentaiions, and its elaborate hair-splittings.

Likewise the negative charge on B induces a positive charge on the side of B' nearest to it and **repels** negative electricity to the far side.