The New Orleans Bulletin

PROTECTION AGAINST LIGHTNING.

At this season of the year a certain class of men, not overscrupulous in their dealings, are in the habit of doing a thriving trade. These men invariably start upon their mission with the first thunder storm of autumn, and follow in its track all over the country. Every death from lightning recorded in any part of the Union serves as an invaluable advertisement to their business, and they reap a rich harvest out of the fears which thunder and lightning inspire. Their stock in trade, it need hardly be said, consists of lightning conductors. We do not mean to imply that this business is not as legitimate as any other. On the contrary, we regard those who are engaged in any way in the work of affording to society that protection and immunity from danger which scientific discoveries guarantee, as benefactors to the race. What we say is that a large number of persons are employed in this business who are more desirous of making money than they are of spreading a true knowledge of science among their customers. All the science they recognize in their transactions is that which brings in the largest amount of profit, and to accomplish this desired end all their inventive faculties are set in motion. The falsest scientific theory which favors their purpose in this respect is sure to be patronized; the most correct will meet with little favor if it is adverse to their interests.

As with most other articles offered for sale, the impression generally prevails that the more expensive the lightning rod which is attached to a building, the more efficient it will prove when struck with the electric fluid. This belief on the part of the public admirably serves the purpose of a class of traders referred to, since it affords them an opportunity of bringing all manner of devices into play in the construction of lightning conductors so as to increase the price. Stars, tubes and crosses, and a variety of complicated inventions, have been introduced into the cross sections, upon the theory that lightning travels only upon the surface of metallic conductors.

Nor are those engaged in this business wholly responsible for this false theory. It has been either upheld or permitted to pass current by many writers on the subject, and has arisen from a mistake which is commonly made of confounding static with dynamic electricity. Perhaps it would be more correct to say that it is to be attributed to an entire ignorance of the real properties of the electric fluid. When electricity is in motion it is dynamic, when at rest it is static. It has been well ascertained that when it is at rest it always tends to diffuse itself upon the surface, and this knowledge led to the belief that electricity in motion followed the same law.

The experiments of the most eminent scientific investigators, however, have long since demonstrated that when electricity is in motion it is conducted, not in the ratio of the surface of the metallic rod, but in proportion to the quantity of metal it contains. This was determined by taking a cylindrical wire of a certain size, and measuring the resistance it offered to a current of electricity, and then flattening the wire and ascertaining the amount of resistance it offered in this condition. The resistance in both cases was found to be equal, although the extent of surface presented in the latter instance was much greater than in the former. This proved conclusively that the conducting powers of a metallic bar depended upon the quantity of metal it contained, and not upon the extent of surface which it presented.

Another method of demonstrating the truth of this theory is by taking a strip of gold leaf about half an inch wide and two or three inches in length, and passing through it a moderate charge from a six-jar electric battery. In this case the gold will be entirely burned up. But if a piece of gold wire one-sixteenth of an inch in diameter be used instead of the gold leaf, though it presents a surface only one fifth of the former, it will carry off the most powerful charge that can be obtained from the same battery without suffering any damage.

The different effects of static and dynamic electricity have also been ascertained by similar experiments, when it was found that a piece of gold leaf was capable of sustaining a very heavy charge of electricity so long as it was allowed to rest in a state of equilibrium; but the moment it became a dynamic by flowing off through the same medium, the gold leaf was destroyed.

The result of scientific investigations has demonstrated, therefore, that the efficiency of a metallic rod depends upon its weight per foot, not upon the extent of its surface. It matters not whether it be round, square or tabular, provided the metal be present in sufficient quantity. Wire and wire ropes, or flat ribbon conductors, are perhaps most convenient, because of the great facility with which they can be placed in position.

The necessity of protecting buildings against the danger of lightning is universally recognized, and while it would be sheer folly to neglect such an obvious precaution, it is well to bear in mind that the most elaborate and expensive lightning-rod is of no more value when struck with the electric fluid than the plainest pattern of conductor, provided it contains an equal quantity of metal.