When properly put up, the lightning rod is a perfect protection; but, when not scientifically constructed, is only a source of danger. The following are essentials: 1. It must extend several feet into the ground so as always to be in contact with moist earth, or into a never-failing supply of water; 2. It must be sharp at the top, and, if there are several points, all the better; 3. It must be half as high above the top of the building as the distance horizontally to the most remote part of the roof of the building; 4. It should be large enough to convey off every discharge without being melted or broken; 5. The best material is iron with copper below the surface of the ground, as iron rusts away rapidly in the moist earth. Copper is the best conductor, but costs more, and is not as stiff to withstand the wind. One-half to five-eighths of an inch in diameter is large enough. Bright points are not essential, and glass insulators are of no use whatever, as when wet they are good conductors, and, even if they were not, a small charge even would leap across the short distance from the rod to the iron staple. The best way to fasten the joints, is to weld them, which any blacksmith can do, passing the rod through opposite doors of his shop, afterwards dragging it home. If the building is so high that it can not be readily put up in one piece, the best joint is made by screwing the two ends firmly into one nut. The points are easily made by welding several smaller wires to the large one, and filing them sharp. A rod will protect a space the distance of which is four times the height of the rod. The cheapest and best support is wood. The only point to be considered is to secure the rod firmly. The round rods are the best. If there are iron water-pipes or steam-pipes in the building, they should all be connected with the lightning rod, or directly with the moist earth, eight or ten feet below the surface.