nor is it of much importance to us [he adds] to know the manner in which nature executes her laws. 'Tis enough if we know the laws themselves. 'Tis of real use to know that china left in the air unsupported will fall and break; but how it comes to fall, and why it breaks, are matters of speculation. 'Tis a pleasure indeed to know them, but we can preserve our china without it.
He anticipated, or, in some instances, all but anticipated, several of the more important discoveries of modern electrical science. He knew that, when a number of Leyden jars are connected up under certain conditions, the extent, to which each jar can be charged from a given source, varies inversely as the number of jars. For a time, he was puzzled by the fact that the light of a candle, or of a fire-coal, or of red-hot iron, would destroy the repellency between his electrified ball and shot, but that the light of the sun would not. But it was not long before he hit upon this ingenious explanation:
This different Effect probably did not arise from any difference in the light, but rather from the particles separated from the candle, being first attracted and then repelled, carrying off the electric matter with them; and from the rarefying the air, between the glowing coal or red-hot iron, and the electrised shot, through which rarefied air the electric fluid could more readily pass.
Referring to what Franklin had to say about the action of sunlight in this connection, Arthur Schuster, in his Some Remarkable Passages in the Writings of Benjamin Franklin, observes: "Had Franklin used a clean piece of zinc instead of iron shot he might have anticipated Hertz's discovery of the action of strong light on the discharge of gases."
In the course of one of his experiments with an electrified can, Franklin reached the conclusion that a cork, which he had lowered into the can, was not attracted to its internal surface, as it would have been to its external, because the mutual repulsion of the two inner opposite sides of the can might prevent the accumulation of an electrical atmosphere upon them. From the same experiment, the genius of Henry Cavendish deduced his law that electrical repulsion varies inversely as the square of the distance between the charges.
Instead of declining, it can truly be said that the reputation of Franklin as an electrical investigator and writer has increased with the progress of electrical science. "We shall, I am sure," remarks Professor J. J. Thomson in his Electricity and Matter, "be struck by the similarity between some of the views which we are led to take by the results of the most recent researches, with those enunciated by Franklin in the very infancy of the subject." Nor should we omit a tribute of Dr. William Garnett, in his Heroes of Science, in regard to the statements in Franklin's first letters to Collinson. "They are," he says, "perfectly consistent with the views held by Cavendish and by Clerk Maxwell, and, though the phraseology is not that of modern text-books, the statements themselves can hardly be improved upon to-day."
If Franklin achieved a higher degree of success in the electrical than in any other scientific field, it was partly, at any rate, because he never again had the opportunity to give such continuous attention to scientific pursuits. To him this was at times a source of very great disappointment. In one of his letters to Beccaria, dated Sept. 21, 1768, he tells the latter that, preoccupied as he was, he had constantly cherished the hope of returning home, where he could find leisure to resume the philosophical studies that he had shamefully put off from time to time. In a letter, some eleven years later, from Paris, to the same correspondent, he said that he was then prevented by similar distractions from pursuing those studies in which he always found the highest satisfaction, and that he was grown so old as hardly to hope for a return of the leisure and tranquillity, so necessary for philosophical disquisitions. To Sir Joseph Banks he was inspired some years later, by recent astronomical discoveries, made under the patronage of the Royal Society, to write: "I begin to be almost sorry I was born so soon, since I cannot have the happiness of knowing what will be known 100 years hence," Indeed, to him, leisure, whether only the seclusion of a thirty-day voyage across the Atlantic, or the final cessation of public life, was but another term for recurrence to his scientific predilections. When he received his leave from Congress to return home from Paris, he wrote joyously to Ingenhousz: "I shall now be free of Politicks for the Rest of my Life. Welcome again my dear Philosophical Amusements." There was, to use his own expression, still too much flesh on his bones for his countrymen to allow him any time except for political experiments; but, for proof of the eager interest that he felt in science, and of the prominent position, that he occupied in the scientific world of America, until the last, we need go no further than the fact that, when he died, the meetings of the American Philosophical Society had, for some time, been held at his home in Philadelphia.
How far Franklin might have added to his reputation as a man of science, if he had not become engrossed by political duties and cares, is mere matter of surmise. But there can be no doubt that he was eminently fitted in many respects for scientific inquiry. The scientific temperament he possessed in the very highest degree. He loved the truth too much to allow the workings of human weakness in himself or others to deface its fair features. In reporting to Collinson the electrical achievements, which crowned him with such just renown, he almost invariably spoke of them as if they were the joint achievements of a group of collaborators, of whom he was but one. The generous alacrity, with which he credits to his friends Hopkinson, Kinnersley, or Syng exclusively special discoveries or inventions, made by them, shows conclusively enough how little this was true. There is no reason to believe that his letters to Collinson on electricity would ever have been published but for the unsolicited initiative of Dr. Fothergill and Collinson; or that they would ever have been translated into French but for the spontaneous persuasion that Buffon brought to bear upon D'Alibard. In a letter to Collinson, after expressing distrust of an hypothesis, advanced by him in former letters to the same correspondent, he declares that he is ashamed to have expressed himself in so positive a manner. Indeed, he said, he must request Collinson not to expose those letters, or, if he communicated them to any of his friends, at least to conceal the name of the author. His attitude towards his scientific triumphs was, when not that of entire self-effacement, always that of unaffected humility.
I am indebted for your preceding letter [he wrote in his forty-seventh year to John Perkins] but business sometimes obliges one to postpone philosophical amusements. Whatever I have wrote of that kind, are really, as they are entitled, but Conjectures and Suppositions; which ought always to give place, when careful observation militates against them. I own I have too strong a penchant to the building of hypotheses; they indulge my natural indolence: I wish I had more of your patience and accuracy in making observations, on which, alone, true philosophy can be founded.
Equally candid and noble are other observations in a subsequent letter to the same correspondent. Referring to certain objections, made by Perkins to his theory of water spouts, he observed: