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ceptible; consequently its various gradations in the extent of the portion $\lambda$ are very easily perceptible. This conclusion is of importance, because it affords the means of presenting to the senses the law of electric distribution even on compound circuits, when it is no longer possible on the simple circuit, on account of its extremely feeble force. It is, moreover, immediately evident, that, with equal tensions, this phænomenon will be indicated with greater intensity, the greater $\lambda$ is in comparison with $\Lambda$.

21. A phænomenon common to all galvanic circuits is the sudden change to which its electroscopic force may incessantly, and arbitrarily, be subjected. This phænomenon has its source in the previously developed properties of such circuits. Since, as we have found, each place of a galvanic circuit undergoes the same alterations to which a single one is exposed, we have it in our power to give sometimes one, sometimes another value to the electroscopic force at any certain place. Among these changes those are the most remarkable which we are able to produce by deductive contact, i. e. by destroying the electroscopic force sometimes at one, and sometimes at another place of the circuit; its magnitude, however, has its natural limits in the magnitude of the tensions.

There is another class of phænomena which is immediately connected with these. If, for instance, we call $r$ the space over which the electroscopic force is diffused in a given galvanic circuit, $u$ the electroscopic force of the circuit at one of its points, which is immediately connected with an external body $M$, and $u'$ the electroscopic force of the same circuit at the same place as it was previous to contact with the body $M$, $u'-u$ is evidently the alteration in the electroscopic force produced at this place; consequently, since this change likewise occurs uniformly at all the other places of the circuit, $r(u'-u)$ is the quantity of electricity which the change produced over the entire circuit comprises, and accordingly that which has passed over into the body $M$. If now we suppose that in the state of equilibrium the electroscopic force is everywhere of equal intensity at all places of the body $M$ in which it occurs, and represent by $R$ the space over which it is diffused in the body $M$, then its electroscopic force is evidently ${\frac {r(u'-u)}{R}}$. But this force is in the state of equilibrium equal to the $u'$, which the