Such effects as this suggest considerable capacity for doing work. Yet in reality, notwithstanding the very sporadical character of the result, the quantity of electricity involved in such a statical current may be very slight indeed. Even a lightning flash is held to represent a comparatively small amount of electricity. Faraday calculated that the amount of electricity that could be generated from a single drop of water, through chemical manipulation, would suffice to supply the lightning for a fair-sized thunder-storm. Nevertheless the destructive work that may be done by a flash of lightning may be considerable, as everyone is aware. But, on the other hand, while the visible effect of a stroke of lightning on a tree trunk, for example, makes it seem a powerful agency, yet the actual capacity to do work--the power to move considerable masses of matter--is extremely limited. The effect on a tree trunk, it will be recalled, usually consists of nothing more than the stripping off of a channel of bark. In other words, the working energy contained in a seemingly powerful supply of statical electricity commonly plays but an insignificant part. The working agent, and therefore the form of electricity which concerns us in the present connection, is the dynamical current. This may be generated in various ways, but in practice these are chiefly reducible to two. One of these depends upon chemical action, the other upon the inter-relations of mechanical motion and magnetic lines of force. A common illustration of the former is supplied by the familiar voltaic or galvanic battery. The electromagnetic form has been rendered even more familiar in recent times by the dynamo. This newest and most powerful of workers will claim our attention in detail in the succeeding chapter. Our present consideration will be directed to the older method of generating the electric current as represented by the voltaic cell. THE WORK OF THE DYNAMICAL CURRENT Let us draw our illustration from a familiar source. Even should your household otherwise lack electrical appliances, you are sure to have an electric call-bell. The generator of the electric current, which is stored away in some out-of-the-way corner, is probably a small so-called "dry-cell" which you could readily carry around in your pocket; or it may consist of a receptacle holding a pint or two of liquid in which some metal plates are immersed. Such an apparatus seems scarcely more than a toy when we contrast it with the gigantic dynamos of the power-house; yet, within the limits of its capacities, one is as surely a generator of electricity as the other. If we are to accept the latest theory, the electrical current which flows from this tiny cell is precisely the same in kind as that which flows from the five-thousand-horse-power dynamo. The difference is only one of quantity.