3767-29590.

SCIENCE

JULY 7, 1893.

Walker Prizes in Natural History.

ELEVENTH YEAR.

VOL. XXII. No. 544.

CONTENTS.

Lacks t.p

3. Experiments affording evidence for or against

the theory of evolution.

Each memoir must be accompanied by a sealed

envelope enclosing the author's name and super-

scribed by a motto corresponding to one borne by

the manuscript, and must be handed to the Secre-

tary on or before April 1, 1894.

Prizes will not be awarded unless the memoirs are

of adequate merit.

NEW METHOD OF PROTECTING BUILDINGS FROM LIGHTNING.

SPARE THE ROD AND SPOIL THE HOUSE!

Lightning Destroys. Shall it be Your House or a Pound of Copper?

SAMUEL HENSHAW, Secretary.

Boston, July 3, 1893,

PROTECTION FROM LIGHTNING.

What is the Problem?

IN seeking a means of protection from lightning-discharges, we have in view

two objects, the one the prevention of damage to buildings, and the other

the prevention of injury to life. In order to destroy a building in whole or in

part, it is necessary that work should be done; that is, as physicists express

:, energy is required. Just before the lightning-discharge takes place, the

energy capable of doing the damage which we seek to prevent exists in the

column of air extending from the cloud to the earth in some form that makes

it capable of appearing as what we call electricity. We will therefore call it

electrical energy. What this electrical energy is, it is not necessary for us to

consider in this place; but that it exists there can be no doubt, as it manifests

itself in the destruction of buildings. The problem that we have to deal with,

therefore, is the conversion of this energy into some other form, and the ac-

complishment of this in such a way as shall result in the least injury to prop-

erty and life.

Why Have the Old Rods Failed?

When lightning-rods were first proposed, the science of energetics was en-

tirely undeveloped; that is to say, in the middle of the last century scientific

men had not come to recognize the fact that the different forms of energy-

heat, electricity, mechanical power, etc.- were convertible one into the other,

and that each could produce just so much of each of the other forms, and no

ore. The doctrine of the conservation and correlation of energy was first

clearly worked out in the early part of this century. There were, however,

some facts known in regard to electricity a hundred and forty years ago; and

among these were the attracting power of points for an electric spark, and the

conducting power of metals. Lightning-rods were therefore introduced with

the idea that the electricity existing in the lightning-discharge could be con-

veyed around the building which it was proposed to protect, and that the

building would thus be saved.

The question as to dissipation of the energy involved was entirely ignored,

naturally; and from that time to this, in spite of the best endeavors of those

interested, lightning-rods constructed in accordance with Franklin's principle

have not furnished satisfactory protection. The reason for this is apparent

when it is considered that the electrical energy existing in the atmosphere

before the discharge, or, more exactly, in the column of dielectric from the

cloud to the earth, above referred to, reaches its maximum value on the sur-

face of the conductors that chance to be within the column of dielectric; so

that the greatest display of energy will be on the surface of the very lightning-

rods that were meant to protect, and damage results, as so often proves to be

the case.

History. ROSE POLYTECHNIC INSTITUTE,

Terre Haute, Ind. A College of Engineering.

It will be understood, of course, that this display of energy on the surface

of the old lightning-rods is aided by their being more or less insulated from

the earth, but in any event the very existence of such a mass of metal as an

old lightning-rod can only tend to produce a disastrous dissipation of electrical

energy upon its surface," to draw the lightning," as it is so commonly put.

Is there a Better Means of Protection?

Having cleared our minds, therefore, of any idea of conducting electricity,

and keeping clearly in view the fact that in providing protection against light-

ning we must furnish some means by which the electrical energy may be

harmlessly dissipated, the question arises," Can an improved form be given

to the rod, so that it shall aid in this dissipation ? "

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As the electrical energy involved manifests itself on the surface of conduc-

tors, the improved rod should be metallic; but, instead of making a large rod,

suppose that we make it comparatively small in size, so that the total amount

of metal running from the top of the house to some point a little below the

foundations shall not exceed one pound. Suppose, again, that we introduce

numerous insulating joints in this rod. We shall then have a rod that experi-

ence shows will be readily destroyed-will be readily dissipated - when a

discharge takes place; and it will be evident, that, so far as the electrical en-

ergy is consumed in doing this, there will be the less to do other damage.

The only point that remains to be proved as to the utility of such a rod is to

show that the dissipation of such a conductor does not tend to injure other

bodies in its immediate vicinity. On this point I can only say that I have

found no case where such a conductor (for instance, a bell wire) has been dis-

sipated, even if resting against a plastered wall, where there has been any

material damage done to surrounding objects.

Of course, it is readily understood that such an explosion cannot take place

in a confined space without the rupture of the walls (the wire cannot be

boarded over); but in every case that I have found recorded this dissipation

takes place just as gunpowder burns when spread on a board. The objects

against which the conductor rests may be stained, but they are not shattered,

I would therefore make clear this distinction between the action of electri-

cal energy when dissipated on the surface of a large conductor and when dis-

sipated on the surface of a comparatively small or easily dissipated conductor.

When dissipated on the surface of a large conductor, a conductor so strong

as to resist the explosive effect, - damage results to objects around. When

dissipated on the surface of a small conductor, the conductor goes, but the

other objects around are saved

A Typical Case of the Action of a Small Conductor.

Franklin, in a letter to Collinson read before the London Royal Society,

Dec. 18, 1755, describing the partial destruction by lightning of a church-tower

at Newbury, Mass., wrote, “Near the bell was fixed an iron hammer to strike

the hours; and from the tail of the hammer a wire went down through a small

gimlet-hole in the floor that the bell stood upon, and through a second floor in

like manner; then horizontally under and near the plastered ceiling of that

second floor, till it came near a plastered wall; then down by the side of that

wall to a clock, which stood about twenty feet below the bell. The wire was

not bigger than a common knitting needle. The spire was split all to pieces

by the lightning, and the parts flung in all directions over the square in which

the church stood, so that nothing remained above the bell. The lightring

passed between the hammer and the clock in the above-mentioned wire,

without hurting either of the floors, or having any effect upon them (except

making the gimlet-holes, through which the wire passed, a little bigger), and

without hurting the plastered wall, or any part of the building, so far as the

aforesaid wire and the pendulum-wire of the clock extended; which latter

wire was about the thickness of a goose-quill. From the end of the pendu-

lum, down quite to the ground, the building was exceedingly rent and dam-

aged.... No part of the aforementioned long, small wire, between the clock

and the hammer, could be found, except about two inches that hung to the

tail of the hammer, and about as much that was fastened to the clock; the

rest being exploded, and its particles dissipated in smoke and air, as gun-

powder is by common fire, and had only left a black smutty track on the plas-

tering, three or four inches broad, darkest in the middle, and fainter towards

the edges, all along the ceiling, under which it passed, and down the wall."

One hundred feet of the Hodges Patent Lightning Dispeller (made under

patents of N. D. C. Hodges, Editor of Science) will be mailed, postpaid, to any

address, on receipt of five dollars ($5).

Correspondence solicited. Agents wanted.

AMERICAN LIGHTNING PROTECTION CO.,

874 Broadway, New York City.