Conductors, are long rods made of iron or other metal, employed for protecting buildings from the effects of lightning.

The utility of conductors is universally acknowledged, yet it has not been ascertained, till within these few years, whether pointed or blunt ones were the most proper : the latter, however, are now decidedly preferred, in consequence of several experiments, made under the inspection of the Royal Sor-Instances, nevertheless, occur of houses provided with pointed metallic conductors, being stricken with lightning ; so that this philosophical contrivance has not yet arrived at perfection. We there-fore communicate, with satisfaction, the following improvement in conductors, made by Mr. Robert Pater son, of Philadelphia, for which the American Philosophical Society adjudged him the prize of a gold medal. He proposes first to insert, in the top of the rod, a piece. of the best black-lead, about two inches long, and terminating in a fine point which projects a little above the end of its metallic socket ; so that if the black-lead point should, by any accident, be broken off, that of the rod would be left sharp enough to answer the pur-pose of a metallic conductor. His second intention is, to facilitate the passage of the electric fluid from the lower part of the rod into the surrounding earth. In many cases, it is impracticable, from the interruption of rocks and other obstacles, to sink the rod so deeply as to reach moist earth, or any other substance that is a tolerably good conductor of electricity. To remedy this de-fect, Mr. Paterson proposes to make the lower part of the rod, either of tin or copper, which metals are far less liable to corrosion or rust, than iron, when lying under ground ; or, which will answer the purpose still better, to coat that part of the conductor, of whatever metal it may consist, with a thick crust of black-load previously formed into a paste, by being pulverized, mixed with melted sulphur, and applied to the rod, while hot. By this precaution, the lowerpartof the rod will, in his opinion, retain its conducting powers for ages, without any diminution.

In order to increase the surface of the subterraneous; part of the conductor, he directs a hole,- or pit, of sufficient extent, to be dug as deep as convenient; into which a quantity of charcoal should be put, surrounding the lower extremity of the rod. Thus, the surface of that part of the conductor, which is in contact with the earth, may be increased with little trouble or expence; a circumstance of the first importance to the security against those accidents - as charcoal is an excellent conductor of electricity, and will undergo little or no change of property, by lying in the earth for a long series of years.