=Insulation of Lightning Conductors.=--It is a question often asked whether a lightning rod should be insulated from the building it is intended to protect. I believe that this practice was formerly recommended by some writers, and I have observed that glass insulators are still employed not infrequently by builders in the erection of lightning conductors; but, from the principles I have set before you to-day, it seems clear that any insulation of this kind is, to say the least, altogether useless. The building to be protected is itself in electrical communication with the earth, and the lightning conductor, if efficient, is also in electrical communication with the earth--therefore, the lightning conductor and the building are in electrical communication with each other through the earth, and any attempt at insulating them from one another above the earth is only labor thrown away. Further, I have just shown you that the masses of metal employed in the structure or decoration of a building ought to be electrically connected with each other and with the lightning conductor. Now, if this be done, the lightning conductor is, by the fact, in direct communication with the building, and the glass insulators are utterly futile. Again, the building itself, during a thunderstorm, becomes highly electrified by the inductive action of the cloud, and needs to be discharged through the conductor just as the surrounding earth needs to be discharged; therefore, the more thoroughly it is connected with the conductor, the more effectively will the conductor fulfill its functions. =Personal Safety in a Thunderstorm.=--I suppose there is hardly any one to whom the question has not occurred, at some time or another, what he had best do to secure his personal safety during a thunderstorm. This question is of so much practical interest that I think I shall be excused if I say a few words about it, though perhaps, strictly speaking, it is somewhat beside the subject of lightning conductors. At the outset, perhaps, I shall surprise you when I say that you would enjoy the most perfect security if you were in a chamber entirely composed of metal plates, or in a cage constructed of metal bars, or if you were incased, like the knights of old, in a complete suit of metal armor. This kind of defense is looked upon as so perfect, among scientific men, that Professor Tait does not hesitate to recommend his adventurous young friends devoted to the cause of science to provide themselves with a light suit of copper, and, thus protected, take the first opportunity of plunging into a thundercloud, there to investigate, at its source, the process by which lightning is manufactured.[36]