Page:Popular Science Monthly Volume 25.djvu/830

812 The Committee of the Meteorological Society, however, seems very soon to have lost sight of its own excellent design, and to have changed its plan into a mere conference for the preparation of a report, which was drawn up under its auspices and printed and published in 1882, apparently by the conference itself, and which assumes the form of a code of rules for the erection of lightning-conductors, with numerous appendices referring to authorities which had been in some sense consulted. The report is published under the editorship of the secretary, and simply as having been considered and adopted by the delegates of the conference, who seem indeed to have concentrated their attention upon one subordinate object which had been proposed by the Meteorological Society, namely, "the diffusion of exact information regarding the best form and arrangement of lightning-conductors," and to have overlooked entirely the more important work of observation and record which had been contemplated by the society in the first instance, and to which we have drawn attention.

The code of rules put forward by the conference was obviously intended to possess the same kind of authority and position as the "instructions" of the earlier French reports, and indeed its chief value seems to be the approval it accords to the practice of construction which had grown out of those instructions, and which is very generally in use at the present day. It virtually confirms most of the conclusions which had been arrived at by the French commissions.

The "Rules" of the London Conference direct that the main stem of the conductor shall consist of a copper rod or tape, with an ascertained electrical conductivity amounting to ninety per cent of that which pure copper would possess, and weighing six ounces per foot; or that it shall be an iron rod weighing two pounds and a quarter per foot; and that the earth connection shall be made by a copper or iron plate presenting a superficial area of eighteen square feet, imbedded in moist earth, and surrounded with coke. The terminal points are to be more prominent than those usually adopted in England, but they may be less so than the heavy tiges of thirty-three feet employed in France. The rod is not to be insulated from the building, but intimately connected with all large masses of metal used incidentally in the construction. All joints in its length are to be imbedded in solder. Curves are not to be made too sharp, and ample provision is to be secured for free expansion and contraction by varying temperature. Water-mains and gas-mains are to be utilized as means of earth contact wherever practicable, and the conducting integrity of the rod is to be tested every year.

A careful perusal of the French instructions, or of Mr. Richard Anderson's very excellent manual upon lightning-conductors, published in 1879, will show that this is substantially an authoritative acceptance of the measures already advised by the best authorities. It is, however, somewhat remarkable that in the report itself of the London