THE MODERN VIEW OF LIGHTNING RODS.

Hot Lakes Chronicle, Issue 116, 20 February 1895, Page 3

THE MODERN VIEW OF LIGHTNING RODS.

The invention of (he lightning-rod was once thought to have solved he jjrobleni of lightning-protection. Failures wero always hsei'ibed.to'bad rods, to faulty contacts, or to imperfect Garth-coimeeUon. Modern views of electricity have let in a flood of light on this subject. A hightonsion discharge like that from a cloud is now known to bo oscillatory, the electrify surging- to and fro many million-times ;i second till equilibrium is established. Theso surgings, too, set up, in surrounding space, electrical waves which spread on all sides and cause induction-currents in ovciy conductor they pasft. The problem, then, is much moro complex than was formerly supposed. No one has done more to popularise theso new views than Professor Oliver J. Lodge, of Liverpool, and though it cannot bo said that all his views are as yet fully established or accepted without reserve, anything that he says carries great weight, and is always profoundly suggestive. From an article by him in tho October Engineering Magazine wo malto the following extracts : —' When an electrified body of any considerable capacity is discharged through i. path of high resistance, tho recovery is comparatively slow; tho current lasts an ap-

prceinblo time, and the only noteworthy result is heat. Tho heat may be of sufficient intensity to make wires red-hot or to ignite gas and gunpowder. In those surrounding it is dangerous; otherwise it may bo considered harmless. Hut when a considerable electrified body is discharged b}' a good conductor, the rush is sudden, violent, and oscillatory. Much less heat is then produced on the spot, but tho noiso and light called an electric flash is developed. A violent shock can bo felt by an animal coming into line with it, and out into space go thoso tremendous waves of which we have been speaking. These waves may simply spread out further and further into space, becoming weaker and weaker as they go, by reason simply of the extent of territory over which their fixed supply of energy has to be spread; but, on the ohier hand, they laoy encounter conductors, and set up la them, by a process analogous to 'acoustic resonance,' electrical BUl'gings of sufficient vigour to predueo sparks, or even to do damage. All flu's is true of tho release of any store of static electric onorgy— of tho discharge or any electrified body. It by no means ceases to be true when the charged body is a square mile or so of cloud. Not only are all the effects spoken of likely to occur then, but they may occur with irresistible and overwhelming violence. No longer can a copper rod, even seveial inches or a foot thick and as long as 3'ou please, be considered a thoroughly efficient protection. Experimentally it can be shown that when a discharge takes place even down such a rod as that, sparks may fly from it to all conductors near, even to quite insulate conductors which lead nowhere. Into space and out again the electricity springs; and,while it is thus flashing about the ramified conducting pipes and wires of a building, woo be to the weak place, the explosive compound, or the gasrleak which it may chance to encounter. "And even if side-flashes from the conductor itself do not happen : to be dangerous in any particular instance, that is no safeguard againt't the furious though evanescent system of waves excited in the surrounding menium. These, as before explained, may excite sparks in perfectly detached and possibly distant conductors : and though such sparks may be far too fecblo to knock out bricks and mortar, everyone who has used an electric gaslighter knows how feeble a spark is sufficient to ignite escapinggas. Moreover, when the dis- ! charge has reached tho earth the danger is not over. A region of earth is for the moment overcharged, and tho charge rushes away as best it may, splashing and surging away in many unexpected places. I have seen a house whoso only important damage was in its cellar, and it stood near a lofty churchi steeple properly protected. I have little doubt that the damage was done by a portion of a flash which had reached earth in'tjie neighbourhoo, and was on its way to dispersiop uuderground. Some obscure fires may be to such causes as theso; more, i perhaps, than have yet been sus-