May not the knowledge of this power of points be of use to mankind, in preserving houses, churches, ships, &c. from the stroke of lightning, by directing us to fix on the highest parts of those edifices, upright rods of iron made sharp as a needle, and gilt to prevent rusting, and from the foot of those rods a wire down the outside of the building into the ground, or down round one of the shrouds of a ship, and down her side till it reaches the water? Would not these pointed rods probably draw the electrical fire silently out of a cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible mischief?
The suggestion was but slowly adopted, not in Europe, indeed, at all, until the efficacy of the lightning rod in protecting buildings had been generally recognized in America. In time, however, the device came into use both in Great Britain and on the Continent; Voltaire being one of the first persons in Geneva to erect one, and, wherever it was erected, it helped to confirm the fame of Franklin by its silent effect upon the human imagination. In recent years, the lightning rod, once in almost universal use in America, has fallen into neglect, but the explanation of this fact is to be found not in any just doubts about its utility, when properly constructed, affixed and grounded, but in the growth of fire insurance, and the inutility, or danger, of such rods, if carelessly set in place.[51]
The domestication of lightning and the invention of the lightning rod were the two things to which Franklin was principally indebted for his brilliant reputation as a philosopher. At this day, the application of electricity to common uses is so familiar to us that it is hard, without a little reflection, to realize how well calculated his electrical achievements were to send a thrill of astonishment and awe through the human mind. Of all the manifestations of the physical world, lightning with its inscrutable, swift, and all but irresistible, stroke, followed by the sublime detonations of thunder, is the one most suggestive of supernatural influence exerted by an all-powerful deity. The mythological dreams of the Greeks, the visions of the Old Testament, the simple emotions of the savage had all paid their homage of dread to the fearful force—like a madman pitilessly destructive, and yet like a madman diverted from its rage by the barest trifle—which had clothed Jove with the greater part of his grandeur, licked up even the water that was in the trench about the altar, built by Elijah in the name of the Lord, and filled the breast of the Indian with superstitious terror. Discovery, that laid bare the real nature and destructive limits of this force, could not fail to excite an extraordinary degree of attention everywhere. It was the singular fortune of Franklin, though a practical, sober-minded denizen of the earth, if ever man was, to have enjoyed in his day a reputation not unlike that of a divinity of the upper ether.[52] It so happens that the atmosphere was, in one way or another, the home of all the scientific problems which engaged his interest most deeply. His philosophical Pegasus, so little akin to the humble brute bestrid by Poor Richard, was "a beast for Perseus—pure air and fire"; and especially, it is needless to say, was this true of his relations to the lightning. When the fact became known throughout the civilized world that human ingenuity had succeeded in even snaring it, Franklin was exalted for a time to a seat on Olympus. All the literature of the period, as well as that of a much later period, bears out the statement that rarely has any single, peaceful incident ever so fired the human imagination.[53] For many years, the natural background for a portrait of Franklin might have been a bank of cloud lit up by the incessant play of summer lightning. Eripuit coelo fulmen sceptrumque tyrannis, was but the mightiest of the electrical discharges that flattery poured upon him. Turn where we may to the poetry of the latter half of the eighteenth century, and of the earlier part of the nineteenth, whether epigram or otherwise, we are likely to come upon some imprint left upon the thought of those periods by the subjugation of lightning.
The interest of Franklin in electrical science was but another sequel of the world-wide avidity with which learned men had recently turned to the study of that subject. One of them, Grey, had pursued a series of experiments for the purpose of determining the relative conductivity of various substances, another, Du Fay, had erroneously classified electricity as resinous and vitreous, and the perfected Leyden Jar particularly had given a new momentum to the progress of electrical investigation. Into this movement, after witnessing Dr. Spence's awkward experiments at Boston, Franklin threw himself with the utmost enthusiasm, and his discovery of the identity of lightning and electricity and his lightning-rod conception were but the chief fruits of this enthusiasm. Between the Autobiography and his letters, we are at no loss to follow closely the steps by which he reached all the results which have given him such a high position as an electrical investigator. "I purchased all Dr. Spence's apparatus ..." he tells us in the Autobiography, "and I proceeded in my electrical experiments with great alacrity." How keen this alacrity became, after he had been rubbing for a time the glass tube, sent over to Philadelphia by Collinson, may be seen in what he wrote to Collinson himself on March 28, 1747:
For my own part, I never was before engaged in any study that so totally engrossed my attention and my time as this has lately done; for what with making experiments when I can be alone, and repeating them to my Friends and Acquaintance, who, from the novelty of the thing, come continually in crouds to see them, I have, during some months past, had little leisure for anything else.
The result of this experimentation was the various letters to Collinson and others that constitute Franklin's highest claim to distinction as a man of science. By following them in their chronological order, the reader can trace with little difficulty the genesis of each of his more valuable conclusions touching electricity. They are distinguished by remarkable simplicity and force of reasoning and by a clearness of statement as transparent as crystal. Moreover, they are even enlivened at times by gleams of fancy or humor. In a word they indisputably merit the judgment that Sir Humphry Davy, no mean judge of style as well as scientific truth, passes upon them:
The style and manner of his publication on electricity are almost as worthy of admiration as the doctrine it contains. He has endeavoured to remove all mystery and obscurity from the subject. He has written equally for the uninitiated and the philosopher; and he has rendered his details amusing as well as perspicuous, elegant as well as simple. Science appears in his language in a dress wonderfully decorous, the best adapted to display her native loveliness. He has in no instance exhibited that false dignity, by which philosophy is kept aloof from common applications; and he has sought rather to make her a useful inmate and servant in the common habitations of man, than to preserve her merely as an object of admiration in temples and palaces.
While recalling these words, it is not amiss to recall, too, what Lord Brougham had to say about the agencies with which Franklin conducted his experiments.
He could make an experiment [said Brougham] with less apparatus and conduct his experimental inquiry to a discovery with more ordinary materials than any other philosopher we ever saw. With an old key, a silk thread, some sealing wax and a sheet of paper he discovered the identity of lightning and electricity.
The truth of these observations is strikingly instanced in a story told of Franklin in Pettigrew's Life of Lettsom. When Henry Smeathman was insisting that the flight of birds is on inclined planes, and that they could not fly at all, but would simply float with the wind, if they were not heavier than the air, Franklin launched half a sheet of paper obliquely into the air, observing, as he watched its course, that that was an evident proof of the propriety of Smeathman's doctrines.