The insulation of the rod from the building is an expense not only without the least advantage, but the contrary. Harris (_Thunderstorms_, pp. 129, 131) says: "This practice is not only useless, but disadvantageous, and is manifestly inconsistent with the principles on which conductors are applied." Dr. Franklin says: "The rod may be fastened to the wall, chimney, etc., with staples of iron. The lightning will not leave the rod to pass into the wall through these staples. It would rather, if any were in the wall, pass out of it into the rod, to get more readily by that conductor to the earth." The practice may have gained vogue from an observance of the use of glass knobs as insulators of telegraph-wires. Many intelligent people have failed to apprehend the vast difference between the low tension of voltaic electricity and frictional electricity, lightning being in the nature of the latter. The fact that when lightning strikes the telegraph-wire it jumps from the wire to the posts, often tearing in pieces half a dozen in a row, ought to be conclusive in regard to insulating lightning-rods. The same considerations will also effectually dissipate the fallacy by which the horizontal lightning-rod has duped so many people in certain portions of the West; for if the wire be cut off from the ground-connections (in which condition it accords with the conductor in question) the posts (which answer to the building thus "protected") must suffer still greater damage. So far from being insulated, the rod should be connected with all considerable masses of metal in the building, these having also a good connection with the earth. Frequently during a thunder-shower--sometimes even on the approach of one--all metallic objects will be electrified, and those of considerable size will often yield a spark; and this without the building containing these objects being struck. When struck, the larger masses of metal might occasion a dangerous explosion from induction, though at some distance from the rod: for this reason, as before stated, they should be connected with the ground. Being then liable to receive a part of the current from the conductor in case this be too small, they should be connected with it, as otherwise the current would cause damage in its passage. In a word, therefore, all metal bodies in a building should, as far as possible, be made a part of the system of conduction. This matter is not well understood generally. A dwelling in Boston having been struck by lightning a few years since, a neighbor remarked that "it was fortunate the lightning did not reach the gas-pipe, for it would then have gone all over the house." The fact was, that the bolt did not go more than five feet inside the house before it struck the pipe, and there all damage ended. The idea may be novel to most people, but if the gas-or water-pipes were carried above the roof to the usual height of lightning-rods, they would form a very efficient system of conductors so