Lightning Rod Conference. Various
as much as possible; but, when they must be made, I scrape the ends of my wire bright, and then splice or interlace them together, covering the whole with thin sheet lead—I object to solder, as I think it must interfere with surface conduction; the wire is fastened to the upper terminal, with a Matthew Walker knot let into a hollow cup, and the terminal screwed down on it.
5. I attach my wire to the building with a brass or gun-metal holdfast 4 inches long, having a ⅝ hole, the inner edge being flush with the wall of the building, so as to allow the conductor to touch the wall of the building all the way up, and still allow plenty of room for the free passage of the electric fluid. I do not approve of insulators, nor yet of that kind of holdfast that is driven in tight on to the wire, for I think that must interfere with the clear passage of the electric fluid.
6. I cut a trench some 15 or 20 feet long, gradually deepening from 1 foot at the commencement to 4 ft. at the termination, which I fill with pounded charcoal and bury the wire in it. Earth-plates are not necessary when this is done.
7. It is calculated that a conductor will protect a surface in the shape of a cone, the diameter of the base of which is equal to the height of the conductor. Thus, if a conductor were 100 feet high, the space protected would be represented by a straight line drawn from a radius of 50 feet from the base of conductor, to a radius of 8 or 10 feet from its highest point.
8. I consider, if there are two terminals, there should also be two wires, or the wire should be of sufficient capacity to carry off a double charge, in case both terminals should be struck at one time. I think the conductors should certainly be of sufficient capacity to carry off any charge that might be received by the terminals, be they few or many.
T. MASSINGHAM.
APPENDIX B.
ANALYSIS OF, AND REMARKS UPON,
THE VIEWS OF MANUFACTURERS.
On Nov. 14th, 1878, a circular was issued to the principal lightning-rod manufacturers in this country, inviting their replies to various questions that were submitted to them, and also any remarks that they might wish to lay before the Conference.
Replies have been received from—
Messrs. Wilkins & Weatherby, of London.
Messrs. Gray & Son, of London.
Messrs. F. Russell & Co., of London.
Messrs. Johnson, Clapham, & Morris, of Manchester.
Messrs. Freeman & Collier, of Manchester.
Messrs. Pennycook & Co., of Glasgow.
Messrs. Davis & Son, of Derby.
Messrs. Massingham, of Newcastle-on-Tyne.
All well-known firms, who have written fully and freely, and whose experience is very extensive.
It is impossible to read these replies without feeling the absolute need of such a Conference as that which has been formed, to collect facts, to digest opinions, and to endeavour to formulate some guiding principles for uniformity in practice—for here we have the most diverse modes of execution detailed, the most opposite views expressed, and the most varied experience narrated. In fact, some ideas enunciated are quite opposed to the teachings of science. Where practice is so opposite, error must abound: and, therefore, there must be great need for an effort to reduce the system of constructing lightning conductors in this country to some uniform basis. On no one single point, except in the use of copper and the necessity for reaching damp earth, do any two manufacturers agree in adopting similar measures.
I will take each question submitted seriatim.
1. Form, dimensions, and material usually adopted for upper terminals.
There are single points and branching points, fine points and blunt points, cones, spikes, balls with spikes on top, and balls with radiating spikes.
The dimensions vary with each form, and they are made of solid copper and copper tube, of brass, of iron, and of gun-metal. The ends are sometimes silvered, sometimes gilt, and sometimes tipped with platinum. But there is no rule or uniformity; and one manufacturer acknowledges that, while he sometimes tips the points with platinum, he considers the practice to be altogether superfluous.
Now it is clear that if there be any electrical efficacy in points as points, they should be made in such a form, and of such a material, as to maintain their efficiency permanently. The writer is very strongly of opinion that the efficiency of lightning conductors is due principally to the peculiar electrical action of their points. He sees no advantage whatever in multiplying these points. In his opinion each conductor should end in one fine platinum point. It would thus act as a dissipator of the electric charge in its immediate neighbourhood, and would then prevent, and not favour discharge. Moreover, points demand frequent inspection, attention, and renewal. He thinks that one function of the Conference should be to examine some of these points in situ, if possible. At present they are erected and left to their fate.
2. The Material and Dimensions of the Conductor.
The use of copper is almost universal, but two manufacturers occasionally use iron. The form varies. The majority use wire rope, but some use rods, others bands or tapes, others tubes. One firm uses a cable “constructed of 49 strands of hard-drawn square copper wire.” Another firm uses a wire rope, simply because “it appears to be an open question, at present, whether it is surface or mass which conducts.” The dimensions are as varied as the form, from a wire rope ⅜th of an inch in diameter to a copper band 3 inches wide and ⅛th thick.
The only point worthy of note is, that no one uses a smaller conductor than a copper rope ⅜th in diameter (i.e. 4 oz. of copper per foot run).
Leaving the dimensions as a question for future investigation, the points submitted for the consideration of the Conference under this head are—
1. Is conduction a question of surface or of mass?
2. Is copper alone to be used?
3. Is the conductor to be in the form of a rope, a rod, a tube, or a band?
Now, on the first point the writer entertains no doubt whatever that the conduction of atmospheric electricity is simply a question of mass, and that the lightning protector acts simply as a conductor obeying the laws of Ohm.
On the second point he sees no objection whatever to the use of iron, when properly galvanized, in situations free from chemical impurities. The reasons urged against its adoption are extremely weak. First, it is said to decay rapidly; and, secondly, it is said to be a very much worse conductor than copper.
The rusting of iron is almost entirely checked, in pure air, by galvanising or coating with zinc. It is used for nearly every other purpose in connection with building, and it is difficult to understand why it should be discarded on account of its liability to decay for this particular purpose, where it is always under supervision.
Again, pure copper conducts about six times better than pure iron: but we never get pure copper in lightning conductors. Moreover, the manufacture of iron wire for telegraphic purposes has increased so enormously during the last two or three years, that the wire now supplied conducts 50 per cent. better than it used to. Hence the difference between the two in this respect is not so great as theory indicates; and it would be well for the Conference to satisfy itself on this point by having similar sized wires made of the