« PrethodnaNastavi »
Terre Haute, Ind. A College of Engineering.
Well endowed, well equipped. Courses in Me-
chanical, Electrical, Civil Engineering, and Chem-
Extensive Machine Shops. Laboratories,
Drawing Rooms, Library. Expenses low. Address
The Boston Society of Natural History|istry.
offers a first prize of from $60 to $100 and a second
prize of a sum not exceeding $50 for the best me-
2moirs, in English, on one of the following sub-
1. The relations of inflorescence to cross-fertiliza
tion illustrated by the plants of Eastern Massa.
2. What depths of formerly overlying rocks, now
4 removed by denudation, may be inferred from the
structure of various rocks in Eastern Massachu.
3. Experiments affording evidence for or against
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-
CONSUMPTION AMONG THE COLORED PEOPLE OF
THE SOUTHERN STATES. G. W. Hubbard..
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?
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
it, 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-
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
more. 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
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
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
A Work of 204 pages, with 3 plates of 12 figures.
Contains full descriptions of nearly one hundred
species of Batrachians and Reptiles, together with
abundant notes on their habits. The identification
of the species made easy by means of analytical
tables. By O. P. Hay, Ph.D. Price, in paper cover,
The Ornamental Penman's Pocketbook of Alpha-
bets, for sign-writers, engravers, stone-cutters and
Howard Cromwell, 50 cts. Practical Electrics: A
A System of Easy Lettering, by
Universal Handybook on Every-day Electrical Mat-
ters, 135 pp., fully illustrated, 12mo, cloth, 75 cts.
Notes on Design of Small Dynamo, by G. Halliday,
with a number of plates to scale, 12mo, cloth,
$1. The Phonograph and How to Construct It, by
W. Gillett, 87 pp., 12 folding plates, 12mo, cloth, $2.
SPON & CHAMBERLAIN, Publishers, 12 Cortlandt
St., New York. Illustrated and descriptive cata-
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 experl-
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
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 wail."
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.,