Masses of Metal.—As far as practicable it is desirable that the conductor be connected to extensive masses of metal, such as hot-water pipes, &c., both internal and external; but it should be kept away from all soft metal pipes, and from internal gas-pipes of every kind, respecting which see page 15. Church Bells inside well protected spires need not be connected.
Earth Connection.—It is essential that the lower extremity of the conductor be buried in permanently damp soil; hence proximity to rain-water pipes, and to drains, is desirable. It is a very good plan to make the conductor bifurcate close below the surface of the ground, and adopt two of the following methods for securing the escape of the lightning into the earth. A strip of copper tape may be led from the bottom of the rod to the nearest gas or water main—not merely to a lead pipe—and be soldered to it; or a tape may be soldered to a sheet of copper 3 ft. × 3 ft. and 1/16 in. thick, buried in permanently wet earth, and surrounded by cinders or coke; or many yards of the tape may be laid in a trench filled with coke, taking care that the surfaces of copper are, as in the previous cases, not less than 18 square feet. Where iron is used for the rod, a galvanized iron plate of similar dimensions should be employed.
Inspection.—Before giving his final certificate, the architect should have the conductor satisfactorily examined and tested by a qualified person, as injury to it often occurs up to the latest period of the works from accidental causes, and often from the carelessness of workmen. (See p. 14.)
Collieries.—Undoubted evidence exists of the explosion of firedamp in collieries through sparks from atmospheric electricity being led into the mine by the wire ropes of the shaft and the iron rails of the galleries. Hence the headgear of all shafts should be protected by proper lightning conductors.
(Signed)
W. GRYLLS ADAMS.
W. E. AYRTON.
LATIMER CLARK.
E. E. DYMOND.
G. CAREY FOSTER.
D. E. HUGHES.
T. HAYTER LEWIS.
W. H. PREECE.
G. J. SYMONS.
JOHN WHICHCORD.
December 14th, 1881.
APPENDIX A.
CIRCULAR AND QUESTIONS
ISSUED TO
Manufacturers of Lightning Conductors,
AND
THEIR REPLIES THERETO.
Note.—There are only two points requiring mention respecting the following replies. First, that in order to avoid useless repetition of the questions, the answers are numbered, and the corresponding question will be found in the following circular. Secondly, that the replies are verbatim, as received from the manufacturers, except that frequent entries will be found in square brackets, e.g. [A 0·11 in.] These represent approximately the sectional area of the conductors, and are given to facilitate the comparison of the conducting capacities of the very various patterns submitted to the Conference.
CIRCULAR.
LIGHTNING ROD CONFERENCE.
30, Great George Street, Westminster, S.W.
November 14th, 1878.
At the invitation of the Meteorological Society delegates have been nominated by the following Societies:
Royal Institute of British Architects,
Society of Telegraph Engineers,
Physical Society,
Meteorological Society,
to consider the present modes of erecting Lightning conductors, and improvements therein.
At a largely attended meeting held this day I was instructed to forward to you the questions stated below, and to request you to forward with your replies any remarks which you may wish to lay before the Conference.
If you desire any specimens to accompany your remarks, I shall be glad if, whenever possible, they do not exceed five inches in length.
I am,
Your obedient Servant,
G. J. SYMONS,
Secretary to the Conference.
QUESTIONS.
(It is requested that the replies be written on foolscap paper, on one side only, and that they be numbered in accordance with the questions.)
1. Form, dimensions, and material usually adopted by you for upper terminals.
2. Material and dimensions of conductor.
3. Is any definite proportion between the length and sectional area of the conductor observed, and if any, what?
4. Joints, how made.
5. Attachment to building, how made.
6. Ground connection, how formed, and of what extent.
7. Extent of area supposed to be protected.
8. If there is more than one terminal, is the size of the conductor increased?
REPLIES.
39, Wapping, London, E.
1. The upper terminals are made of a copper tube ⅝ inches in diameter and 1/16 inches thick [A. 0·11 in.] In the upper end of the tube is fitted 15 inches of copper rod tapered to a point at the top, into which is fixed 3 or more smaller rods about ¼ inch in diameter [A. 0·05 in.] each tapered to a point, and brought into the parent rod in a curve (not at an angle). The next part of the tube, down to about 9 inches from the bottom, is filled with a stiff iron rod to strengthen it, the lower end of the tube being left open to receive the rope. This constitutes what is called “the point.” These points vary in length from 2 or 3 to 8 or 10 feet when used for buildings. A square-topped tower would require a much higher point than would be necessary for the top of a spire.
Sometimes the points are tipped with platinum, which we consider to be altogether superfluous.
2. The conductor is simply a wire rope, varying in size, and mostly either ⅜,½, or ⅝ inches in diameter [A. 0·11, 0·20, or 0·31 in.] These ropes are made in two different forms: the one ⅜ inch diameter [A. 0·11 in.], most suitable for ships’ use, is composed of 49 No. 18 guage copper wires, each wire having a circumferencial measurement of ·157 inches [A. 0·002 in.]; the circumferencial or surface measurement of the whole of the 49 wires is equal to 5·693 inches [A. 0·11 in.], or say, equal to the surface of a copper band 2·846 inches wide—i.e., measuring both sides of the band.
The other make, say ½ inch diameter [A. 0·20 in.], much used for lofty buildings, is composed of 7 No. 7 guage copper wires, each wire having a circumferencial measurement of ·581 inches [A. 0·027 in.]; the circumferencial or surface measurement of the 7 wires