[A. O·18 to 0·24 in.] in two or three branches, with forks at end of each band, and, if water is not near, the trenches half filled with carbonaceous materials and well watered, as this material will readily absorb the least moisture and retain it, while being in itself the best conductor. But much will depend upon the nature of the ground; for if chalk or rock foundation and water cannot be got at, the ground branches must be at least doubled, and the trenches deeper and made up of carbonaceous materials and earth.
7. Our experience is that no appreciable extent is protected by a single rod conductor in the presence of other influences. The chimney-stacks, lined with carbon in the shape of soot, with the heated gases, cause a rarefaction in the atmosphere, and form an easier passage for the electric fluid. Roofs and buildings having large masses of metals will be more likely to influence lightning than the single line of copper rod generally fitted. Many cases have occurred of chimney-stacks 4 feet to 9 feet across being struck opposite the conductor, and lead roofs, gutters, lead ridges, &c., from 10 feet to 20 feet from the rod conductor.
8. No; the system of conduction used by us does away with this, the lines of conduction being ample.
Remarks.
From our close connection with the late Sir William Snow Harris, adviser to the Crown for upwards of twenty-five years in regard to lightning conductors for the navy, and having made lightning conductors our especial practical study for thirty-five years, we may be pardoned for making a few remarks on the protection of buildings from lightning.
We would, firstly, say that the system of conductors now fitted by us is based upon these past years of experience, and upon facts collected during this period, of accidents to buildings having the ordinary single line of conduction, as also from the practical success of the conductors in the navy.
The form of conductors used by us has been adopted after considerable experience, as being the most simple, solid, durable, and capacious form of conductor for the safe conduction of heavy strokes of lightning.
In place of insulators as fastenings, we use copper holdfasts, as we found the former dangerous and useless, as the glass, being non-conductive, the expansion and heat of the electric fluid, being confined, broke them, and caused an unsafe concussion; and it is also a disadvantage for a conductor to be away from the building, as nearly every material in nature assists, without detracting from, the safe discharge of the electric fluid through a good copper conductor. We find that the copper wire rope conductor, usually applied, is seldom more than ⅜th of an inch in diameter; but we did once remove, from the tower of St. Mary’s Church, Taunton, a copper wire rope conductor of ⅞th of an inch in diameter [A. 0·60 in.], said to be especially made to order—certainly the largest we ever came across; but it failed to give the necessary protection in a lightning storm, which did much damage to the tower and roof of the church. As capacity or weight of copper is the most important for safe conduction, copper wire rope is very deceptive in this respect, as will be seen by the following comparisons, viz.:—A copper wire rope conductor of ⅜ inch diameter [A. 0·11 in.] weighs 2¾ ounces per foot, not equal to a plain solid band ⅜ inch wide and ⅛ inch thick [A. 0·046 in.], which weighs 2·907 ounces per foot. A copper wire rope conductor of ½ inch diameter [A. 0·20 in.] weighs 5 ounces per foot, not equal to a solid band of ¾ inch wide and ⅛ inch thick [A. 0·092 in.], which weighs 5·814 ounces per foot. A copper wire rope conductor of ⅝ inch [A. 0·31 in.] weighs 9½ ounces per foot, not equal to a solid band of 1¼ inch and ⅛ inch thick [A. 0·153 in.], which weighs 9·690 ounces per foot. This is the largest size of wire rope conductor made or used.
From the above will be seen what protection can be given by conductors of such small capacities; and we may add that solid band conductors of the same weight, and superior in every way, can be fixed at less than half the cost of the wire rope, foot for foot.
Copper chains and copper wire bands, as conductors, answer in so uncertain a manner with the galvanometer, that they should never be used.
Iron in any form should be avoided, from its lower conducting power, and its utter uselessness when in a rusty and decayed state.
With regard to testing with the galvanometer, the mere testing of the conductors is no proof of the security of the building itself. We not only test the conductors, but also the building, to prove that it is under safe conduction in lightning storms.
In conclusion, we beg to state that our patent system of protection is the application of one or more main down and ground copper conductors and sizes, according to the height and area of the building, the fitting of the copper bands to each chimney-stack, and connecting the same, and the connecting of all the metals on the roofs thereto and to the main conductor, so that there shall be no circuit by which the lightning fluid would be likely to attack without having its exit to the main conductor.
For high working chimney-shafts we fit a copper band round the top, and four points thereon connected to main down conductor.
For further information, we earnestly solicit the careful perusal of our pamphlet and papers herewith.
J. W. GRAY & SON.
Chippendale Mews, Harrow Road.
1. Upper terminals pointed with one or more points, according to the nature of the building to be protected. Dimensions vary in like manner. Material—copper or brass, with electro-gilded points.
2. Conductor composed of copper or galvanized rope, according to height, &c., of building, &c., dimensions varying with resistance of the circuit.
3. The sectional area varies with the length.
4. Joints made, as far as possible metallically; where solder cannot be used, screw joints are made use of.
5. Attachment to building direct by metallic ties of requisite form.
6. Ground connection—When practicable, the end of conductor is metallically connected with gas or water main, otherwise a hole is dug deep enough to meet always moist earth. The end of conductor is either attached to an earth plate, or coiled up in a bundle and surrounded by coke.
7. The area protected is supposed to be a radius equal to the height of conductor.
8. If more than one terminal is attached to one conductor, the size of the latter is increased, except under certain conditions.
F. RUSSELL & CO.
137, Princess Street, Manchester.
1. A copper tube 1¼ inch diameter or 1 inch diameter, finished at the upper end, with a forged copper point or cone, connected with the tube by a cast copper (or gun-metal) coupling, into which coupling are also screwed three or more smaller points round the larger central one. At the lower end the tube is screwed into a somewhat similar coupling, to receive also the brazed and screwed end of the conductor. Or a solid copper rod ½ inch diameter [A. 0·20 in.], or wrought iron rod 1 inch diameter [A. 0·79 in.] (where iron conductors are used) the rod in either case forged to a blunt point, and screwed at the lower end, like the tube first described, to fit the coupling.
2. (a). Copper wire rope of 7 strands each, No. 10 Birmingham wire gauge, or in specified cases of No. 8 or 7 wire gauge, making, when spun, a rope with a sectional area varying from 7/16 to 11/16.
(b). Solid copper rods ½ inch diameter [A. 0·20 in.].
Solid iron rods 1 inch diameter [A. 0·79 in.].
(c).
