Chapter XXVIII: Appendix: L

ON THE LIGHTNING CONDUCTORS AT THE PARIS INTERNATIONAL ELECTRICAL
EXHIBITION, BY MESSRS. DYMOND AND SYMONS.

It was hoped that at the Paris Electrical Exhibition would be found examples of the various styles and patterns of lightning rods used in the several countries of Europe and in the United States, and we accordingly visited the Exhibition and inspected all the exhibits in any way relating to the subject.

Those from France were naturally the most numerous (15), but there were some very elaborate specimens of the system adopted in Belgium, in accordance with the recommendations of M. Melsens; and there was also sent by Dr. Weber, of Kiel, a very interesting collection of 12 points which had been struck by lightning, all more or less fused and damaged.

The French exhibitors showed a great variety of points, but they were for the most part referable to two or three types or classes, and only varied in size. The favourite form appeared to be that shown by Fig. 1, a rather finely tapering brass rod terminated by an acornshaped piece, from the upper end of which projected a small needle. They were constructed to be screwed to the top of the iron _tige_. They varied in size from 1 ft. long and ¾ in. diameter at the base, tapering to ¼ in. at the acorn, to 2 ft. 6 in. long and 1¼ in. diameter, tapering to ¼ in. The acorns were generally about twice the diameter of the point to which they were joined, and were about 1½ diameter long. The needles were always made of platinum about 1½ in. long and ·1 in. diameter. Some exhibitors showed a very similar pattern, but made in copper instead of brass. There were also several specimens of blunt points in copper—the _Point Municipal_, Fig. 2, tapering from 1 in. to ½ in. diameter and 1 ft. 8 in. long; tapering brass and iron rods, some of them having platinum cones, were also exhibited. All these points were intended to be mounted on exceedingly long upper terminals.

The conductors were generally made of wire rope, copper, brass, or galvanized iron, and in the majority of cases composed of strands of small wires, though there were a few specimens of ropes made of large wires (say) ·1 in. in diameter; and there were also some specimens of conductors made of iron bars with copper expansion bands. These last specimens were about ·8 in. square, but almost all the ropes seemed to us too small, generally about ·4 in. diameter, and we were surprised to see that the iron ropes were no larger than the copper or brass ones.

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The methods adopted for joining them to the upper terminals were either to push the end into a socket and pin them across, or more frequently to tie them more or less loosely round the base.

The practice as to insulation seemed to vary, some makers supplying insulators and others not, but they almost all provided for carrying the conductor from 6 to 9 in. away from the face of the building.

There were but few specimens of earth plates, they were in the form of grapnels, and seemed very inadequate; not one would afford 3 superficial feet of earth contact.

Some models and drawings showed that the French electricians assumed a cone of protection whose radius was at least 1·75 of its height. (See ante page (67).)

Excepting France the most numerous series of exhibits was that from Belgium, which also contained a complete model of the monument erected at Lacken in memory of Leopold I., showing the manner in which it had been fitted with conductors under the superintendence, or according to the system, of M. Melsens.

The monument referred to is a ten-sided Gothic building, with pinnacles on two storeys and a spire. On the top of the spire, but below the figure, is a considerable number of radiating points, and there is a similar frill round the top of each of twenty pinnacles. Each aigrette consists of seven copper points, each about 0·4 in. in diameter and 2 ft. long, tapering to a very sharp point; they are all leaded into a collar or band encircling the stone work; and from them go the rods about 0·4 in. in diameter, which are first taken into a cast iron box about 8 in. × 5 in. × 2 in.; into this box are also taken rods which lead to connections with (1) a well, (2) the water mains, and (3) the gas mains. When these two series of rods are all in position in the box it is filled with melted lead, and thus perfect connection is secured. There were specimens of the aigrette, and also of the manner of joining the rod to the gas and the water mains, and to the large iron pipe which is sunk in the well. This is effected by bringing all the rods parallel with the main, and arranging them, at equal distances from each other, around it. They are then held tightly to it by two semicircular clamps bolted together, and melted lead is poured in and caulked. The main, and probably the inside of the clamps, was filed bright when the joint was made.

The other exhibits—patterns of points and conductors—do not call for any special mention, but we may notice that the Belgian makers were generally much more careful than the French to make good electric contact at the joints, and some conductors were exhibited cut through the joints to show the care bestowed in this particular.

From Germany were sent some specimens of wire rope for conductors, made of the usual strands of small wires. The iron ropes were slightly larger and of slightly larger wires than the copper, but the former were not more than 0·6 in. in diameter.

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Dr. WEBER, of Kiel, exhibited a collection of 12 points, all which have been struck by lightning—their length varies from 4 in. to 7 in., they are of gilded copper, about 1 in. in diameter at the thickest point, and vary in the acuteness of their extremities—some have platinum needles, about 0·08 in. diameter, screwed into their points; these needles have, in most cases, been wholly fused. In some cases the platinum is somewhat thimble-shaped, and fitted over the copper—in these cases the platinum is generally wholly melted, and the copper uninjured. Platinum of 0·12 in. diameter has been melted, but there is not one of these points of which copper of that size has been fused. There is no indication that these points have been fixed to tiges—on the contrary, they are all hollow at the base, and have had soldered into them copper ropes, none exceeding 0·33 in. diameter, and most of them consisting of three strands of six wires each (=18 wires), the wires being about No. 18 B.W.G.

There were a few specimens of gilded copper points, sent from Austria, such as Fig. 3; and our English makers also sent a few examples of points, the crow foot, Fig. 4, for instance, of upper terminals, and of rope and tape conductors.

E. E. DYMOND.

G. J. SYMONS.