If the building be large, there should be a rod at each end; and it is an additional security, if these rods be connected by a piece of metal, running from the one to the other, on the roof of the house. If there be but one rod, it should, in this country, be put on the western end of the house; because thunder storms oftenest arise from that quarter. If the position of the house affords but little choice in this respect, the rod should be placed either on the kitchen chimney, or as near to it as possible; because smoke and heat are conductors, and in the summer, smoke and heat seldom ascend from any other chimney than that of the kitchen. When there is a copper spout to a house, the rod, if convenient, may be connected with it as a part of the conductor. In this case however, care should be taken to make the connexion complete, both at top and bottom. Large barns and barracks, have even more need of a rod to preserve them from lightning than a dwelling house, because the vapour which ascends from them when filled with vegetable substances, imperfectly dried, is a powerful conductor. Ships, and all vessels which have high masts, have as much need of conductors as houses on the land. Copper conductors are in every view the best for ships, as they will not contract rust from sea water. A conductor, of this metal, should be attached to the highest mast of the vessel, and extend three or four feet above its top. It should be inserted into the side of the mast, so as to leave the surface smooth, be carried across the deck and over the side of the ship to the keel; so that it may terminate where the lower extremity may be always under the water. Chains are often used as conductors to ships, but they are far inferior to a piece of metal, whose parts are not separated. In the above directions it has been our aim to show in what manner structures may be best and most effectually protected against danger from lightning, and whenever it is practicable the best means ought certainly to be used. But it is to be remembered that where means the most effectual cannot be applied, those of an inferior kind are not to be neglected. A small rod, however pointed or fastened to a house, is unspeakably better than none, and a chain should always be used in a ship, if a rod cannot be obtained. In ninety nine cases out of a hundred, any metallic conductor, reaching from the top to the bottom of a structure, will preserve it from destruction by lightning, and save the lives or property of the inhabitants, when the whole might otherwise have been destroyed. The points of rods have often been found melted by lightning, and both they and the lower extremities are often injured by rust. For an effectual method of preventing both these inconveniencies, the public are indebted to Robert Patterson Esq. professor of mathematics in the University of Pennsylvania, and director of the Mint of the United States.—His memoir on the subject is as follows:—