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ELECTRICITY.
As far as military purposes are at present concerned, we have four principal subjectsof application for what practical knowledge is available on this head.
1. The Lightning Conductor.
2. The Electrotype.
3. The Explosion of Mines.
4. The Electric Telegraph, as associated with railroads considered as military
communications.
In No. 1, the object is to permit a free neutralization of the electric forces, andthus, as it were, to afford a ready outlet to a violent agency that may do mischief toan indefinite amount, if not provided with such means of escape,—in short, “ to makea bridge of gold for a flying enemy,” though it will be shewn shortly that gold is nolonger considered the best material for that purpose.
In Nos. 3 and 4 the object is to apply to the work intended for it this samepower when created and accumulated to any desired extent, by apparatus for effectingthe changes before mentioned in either the mechanical or chemical constitution ofcertain bodies.—See ‘ Telegraph ’ and 1 Voltaic Electricity.’
LIGHTNING CONDUCTORS.
The following notices are intended to embody such principles as are involved inarrangements for lightning conductors. The practical parts have been abridged fromSir W. Snow Harris ’s different works, especially that on Thunder-storms; though,respecting any difference there may be between the more theoretical portions of thesubjoined and his, it is to be observed, that in arguing on the general development ofelectricity, that distinguished author’s reasoning is built on the Leyden hypothesisof opposed surfaces.
The distinction between ‘ Conductors ’ and ‘ Non-Conductors ’ is arbitrary; andthe line of conduction in all bodies may be considered to lie along the polarizedmoleculse composing that line,—whether we refer to metals as so-called ‘ Conductors,’or to the air as an assumed ‘ Non-Conductor :’ in both the electric action passesfrom atom to atom along the course taken, though with far greater rapidity in theone case than in the other. In this view of the atmospheric particles forming linesand (thence as connected laterally in mass) spaces of conduction, it is considered thatelectricity is being perpetually evolved from the earth (as from a huge electricmachine) by the incessant changes in the mechanical as well as chemical condition ofits constituents; such changes, for instance, as those accompanying variations oftemperature produced by the enormous extent of evaporation* from the land andfresh water, as well as from the ocean,f—by the absorption and re-irradiation ofsolar heat; by the escape of central heat; or by the decomposition and recompositionperpetually in progress over the face of the earth, of all descriptions, from slowputrescence to rapid combustion, &c., &c.,—all of which are, more or less, associatedwith changes in electric condition.
This excited electric condition of the gaseous or other volatile bodies, thus releasedin their course upwards through and mixed with the atmosphere, cannot but disturb theelectric equilibrium of its particles inductively; and this action continues till the processreaches the nebulous matters consisting of these vapours, &e., condensed into clouds