A lightning conductor, said Professor Pouillet, is destined to act in two ways. In the first place, it offers a peaceful means of communication between the earth and the clouds, and by virtue of the power of points the terrestrial electricity is led gently up into the sky to combine with its opposite. In the second it acts as a path by which a disruptive discharge may find its way to the earth freely. In the latter case he considered there was a risk of a sharply tapered point becoming fused, and recommended that the angle of the cone at the top of the air-terminal should be enlarged. He also advised that the point should be made of red copper instead of platinum, and based his argument on the fact of copper being a better conductor of electricity than platinum, and considerably cheaper. A copper point, remarks M. Pouillet, subjected to a heavy stroke of lightning, would be much less heated than a platinum point, and would scarcely in any case be fused. While in the report of 1823, iron ropes were recommended almost exclusively as the best material for conductors for ships, the ‘Instruction’ of 1854 declared strongly in favour of copper as the far superior metal for the purpose. ‘Copper,’ affirmed Professor Pouillet, ‘is superior to iron as well as to brass for the purpose of lightning conductors, it having the advantage not only of being less influenced by atmospheric agencies, but the still more important one of allowing a freer passage to the electric force of over three to one. Copper should therefore be exclusively used in the construction of lightning conductor cables for the protection of ships.