electricity or magnetism is concerned. It is not to be taken in its literal sense as applying to something which has bulk and weight. A steel bar, after being magnetised, weighs exactly the same as before, yet its ends exhibit certain properties which we may conventionally ascribe to accumulations of magnetic matter which, if brought near magnetic matter adhering to the end of some other magnetised bar, becomes "active matter" in the sense of producing either attraction or repulsion. The force is attractive if the ends of the bars brought near each other contain magnetic matter of opposite sign, and it is repulsive if the magnetism is of the same sign.
In the same way there is repulsion between two conductors both positively or both negatively electrified, and there is attraction if one is positively and the other negatively electrified. Also in this case electrification does not alter the weight of the conductor, although we may consider the electricity carried by the conductor as an "active mass" in the sense that the force of attraction or repulsion acting through space is due to it. In gravitation the force is always attractive, whilst with magnetism or electricity as active matter the force may be either attractive or
