as lightning conductors. With our present knowledge of electrical phenomena, and the practical art of making conductors, it may safely be affirmed that the Munich professor was right in recommending ropes, though not in approving of brass as the best metal. In its very nature, brass, a compound, can never be thoroughly reliable, because its conducting power varies according to its composition. The facility with which it allows the electric force to pass through it depends, in fact, entirely on the amount of copper which brass contains, and is greater or less accordingly, since the other metal entering into its composition, zinc, has less than one-third the same conductivity. Now brass is, for various purposes, made sometimes of 70 parts of copper and 30 parts of zinc, and again, only equal amounts of both metals, setting calculation as to its conducting power entirely at nought. But besides this, brass has the great fault of being excessively liable to destruction by atmospheric influences, and it was found, among others, in Germany, that while brass ropes were used as lightning conductors, they were frequently destroyed, in a comparatively short space of time, by the action of smoke alone. It is true, the Continental mode, existing both in France and Germany, of spanning conductors over the tops of chimneys--illustrated in the engraving here as a warning ‘how _not_ to do it’--had much to answer for this atmospheric deterioration, since even tougher metals than brass could not be expected to stand the constant action of smoke, often containing sulphurous fumes. But even without such an evidently absurd arrangement as that of running any conductors, whether in the form of ropes or cords, across the orifices of chimneys, brass could never have answered all the requirements of a lightning conductor. It was with justice that brass-wire ropes were nearly altogether discarded some thirty or forty years ago, after having had a short-lived reputation. [Illustration]