APPENDIX B.ANALYSIS OF, AND REMARKS UPON,THE VIEWS OF MANUFACTURERS.

T. MASSINGHAM.

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.

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 submittedseriatim.

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 pointsas 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 thenprevent, 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 pointsin situ, if possible. At present they are erected and left to their fate.

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-drawnsquarecopper 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 two materials, and having them measured electrically for their resistance.

But it has been pointed out by the late Mr. Brough (Phil. Mag., May, 1879), that by regarding (1) the influence of the rise of temperature, (2) the difference between the specific heats, and (3) the relative dimensions, iron conductors can be made much smaller than was formerly supposed: and, that as iron is so much cheaper, iron rods can be made equally efficient for a much less sum than copper. Moreover, the use of iron enables the architect to use one kind of metal throughout his structure, and thus avoid anywhere the contact of dissimilar metals, which always results in decay.

On the third point, the writer is clearly of opinion that a galvanized ironropeis amply sufficient for country residences and buildings free from chemical actions. In such places, and in towns, copper should be used. A rope, whether of iron or copper, is easily handled, it can be made of any size, it can be led in any direction without bends or angles, it is neat and easily jointed, diverted, or lengthened.

The writer refrains from expressing any opinion on its dimensions here, for this is a point that will require most careful examination by the Conference.

The majority of the manufacturers increase the size of theconductors for high buildings—one making the limit 120 feet, another 150 feet, while a third “varies the sectional area with the length.” One firm does not consider any difference necessary, while another takes it that the sectional area should be the same irrespective of length, for “lightning does not vary in intensity while passing through a conductor of greater or less length.”

Now, the laws of electricity clearly show that to maintain equal efficiency we must vary the sectional area as we increase the length of the conductor; but it is a question for the Conference to decide whether we should not recommend a rope of uniform dimensions that would be equally applicable for high and low buildings. Within ordinary limits the necessity for increased thickness for increased height is scarcely evident, but the remedy of an increased sectional area, with the number of separate points erected, is very clear. Indeed, each point should be the terminal of a conductor, whose sectional area should be uniform to the earth. For if it be not so, and each conductor be fully charged with electricity, then when the sectional area diminishes there will be congestion, resulting in heat and discharge to the building. Hence the thickness of the main conductor must increase with the number of separate points erected.

Some are rivetted, others are screwed, others are coupled by right and left-handed screws. Tubes are socketed into each other. In one case “the end of the conductor is knotted and drawn through a cup-shaped ring of metal.”

There can be no doubt that joints are the greatest source of danger in lightning conductors. If a joint be imperfect, and the conductor be conveying a charge to earth, heat will be generated there, the conductor may be fused and rendered useless, and the discharge will be diverted to the building. Or the joint may be so bad—that is, its resistance may be so great—that it renders the conductor practically useless, for other parts of the building will offer easier paths to the earth. Though the use of solder is pretty general, it is not universal. Indeed, one manufacturer objects to it because “it must interfere with surface conduction!” It certainly should be imperatively used. No joint can possibly be perfect that is not metallically continuous. Careful soldering is the only certain mode of securing this, and that this is practicable is evident from the millions of perfect joints in telegraph wires. To scrape the ends of wire bright, and cover the whole with thin sheet lead, as is done by one firm, is simply to court danger. The absence of joints in wire rope is one great element in its favour.

5.Attachment to building, how made.

Some attach the conductor to the building by copper straps and nails; some use holdfasts, either of copper wire or gun metal; others use staples; one uses metallic ties. Several pass the conductor through insulators of glass, porcelain, or earthenware. But the majority discard insulators as useless.

In the opinion of the writer they are quite right, for it is difficult to understand what useful function the insulator performs. One fact that occurred in 1837 is given as a reason for their use, but the fact militates against the efficiency of the conductor rather than the absence of insulators. If the conductor were perfect there could have been no concussion at the point of attachment. If it were imperfect there may have been, for the discharge would seek other paths to earth. Some manufacturers use holdfasts of a different metal to that of the conductor. This is wrong, for where different metals are used galvanic action sets in, tending to decay and rupture. The attachments for this reason should always be of the same metal as the conductor.

The necessity for reaching moist ground is generally recognised, but various curious ways for making earth connection are suggested. One firm considers that a band cut into strips 18 inches long would suffice, while another says that not less than 30 feet, in two or three branches, with fork at the end of each band, should be used. One firm is very brief: “Ground end is coiled loosely in damp earth or a well.” The use of coke, powdered charcoal, or carbonaceous materials, is insisted upon by others.

It is questionable whether the difficulty of fitting a good connection with the earth is fully realized. None but telegraphists know the great difficulty there is in doing this. The first object to be secured is a good damp soil, and the next as large a conducting surface as possible. Metal pumps, iron, gas, or water pipes, wells in which plates of metal 2 or 3 feet square are placed, or similar plates may be buried in perpetually damp ground, or in holes well filled with powdered coke. Moisture in some form is essential, and without it a lightning protector is of small service.

The majority of the firms consider that the area protected has a radius equal to the height of the conductor; but one firm considers that this should be multiplied by five or six times; while another asserts, “that no appreciable extent is protectedby a single rod conductor;” and another, that “many instances may be related of buildings being struck much within the radius of well protected churches or chimneys.”

We have no experience at present to enable us to form a definite opinion on this point. The Committee of the French Academy, gave the radius as equal to twice the height of the conductor from the ground, but buildings have undoubtedly been injured within this limit. The writer does not think that a greater radius than the height should be taken: but thinks that this is one of the most important questions that the Conference could determine. Calculation might, to a certain extent, settle the point: but it is more a case for experience.

This question has been partially considered. (See No. 3.)

Some firms do not consider any increase necessary: others think that when two or more terminals are used, the main rope should be somewhat enlarged; while others run one cable from each terminal, or make the conductor of sufficient capacity to carry off the double charge.

The writer considers that every conductor should be complete in itself: or, if this is inconvenient, then the size of the main conductor should be enlarged in proportion. It does not at all follow, as one firm implies, that if two or more terminals receive the charge simultaneously, it is necessarily sub-divided. Each charge may be full and complete in itself, and be sufficient to fill the wire; and, therefore, if the main conductor be not increased, accident may result.

There is no doubt whatever that great consideration should always be given to the lessons of experience, and the opinions of those who have made the erection of lightning conductors for 35 years their especial practical study, are much entitled to weight; but such practice may have originally been based on error, and the teachings may not have been guided by science. Where such variety of practice abounds, there must be fallacy somewhere, and, therefore, danger; and not the least of the beneficial labours of the Conference will be to point out to these different practical men, where their faults and their departures from truth exist.

W. H. PREECE.

August 8th, 1879.

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