Under these prosperous circumstances, Franklin withdrew from active business, became a silent partner in the firm, and devoted nearly all his time to the new science. He wrote, in the autumn of 1748, to his friend Cadwallader Colden of New York,
“I have removed to a more quiet part of the town, where I am settling my old accounts, and hope soon to be quite master of my own time, and no longer, as the song has it, ‘at every one’s call but my own.’
“Thus you see I am in a fair way of having no other tasks than such as I shall like to give myself, and of enjoying what I look upon as a great happiness, leisure to read, study, make experiments, and converse at large with such ingenious and worthy men, as are pleased to honor me with their friendship or acquaintance, on such points as may produce something for the common benefit of mankind, uninterrupted by the cares and fatigues of business.”
He wrote a treatise upon thundergusts, which displayed wonderful sagacity, and which arrested the attention of nearly all the philosophers in Europe and America. The all-important topics of this exceedingly important document, were the power of points to draw off electricity, and also the similarity of electricity and lightning. He therefore urged that metallic rods might be attached to buildings and ships, which, pushing their needle points above roofs and masts, might draw the electric fire harmlessly from the clouds. He confesses that he cannot imagine why the points should possess this curious power, but urges that facts seem to demonstrate it.
One day, for the entertainment of his friends, he had made arrangements to kill a turkey with an electric shock. Two large jars were heavily charged. Incautiously manipulating, he took the shock himself. In the following language, he describes the effect:
“The flash was very great, and the crack was as loud as a pistol; yet my senses being instantly gone, I neither saw the one nor heard the other; nor did I feel the stroke on my hand, though I afterwards found it raised a round swelling where the fire entered, as big as half a pistol bullet.
“I then felt what I know not well how to describe, a universal blow throughout my whole body from head to foot, which seemed within as well as without; after which the first thing I took notice of was a violent, quick shaking of my body, which gradually remitting, my sense as gradually returned, and then, I thought the bottle must be discharged, but could not conceive how, till at last I perceived the chain in my hand, and recollected what I had been about to do.
“That part of my hand and fingers which held the chain, was left white as though the blood had been driven out; and remained so eight or ten minutes after, feeling like dead flesh; and I had numbness in my arms and the back of my neck which continued to the next morning, but wore off.”
Franklin was much mortified at his awkwardness in this experiment. He declared it to be a notorious blunder, and compared it with the folly of the Irishman, who wishing to steal some gun-powder, bored a hole through the cask with red hot iron. But notwithstanding this warning, not long afterwards, in endeavoring to give a shock to a paralytic patient, he received the whole charge himself, and was knocked flat and senseless on the floor.
In the spring of 1752, Franklin tried his world renowned experiment with the kite. A June thunder cloud was rising in all its majesty. Franklin, accompanied by his son, repaired to a field secretly, being afraid of the ridicule of the people. Here he raised the kite, made of a large silk handkerchief. The top of the perpendicular stick was pointed with a sharp metallic rod. The string was hemp with the exception of the part held in the hand, which was silk; at the end of the hempen string a common key was suspended. With intense anxiety and no slight apprehension of danger, he held the line. Soon he observed the fibres of the hempen string to rise and separate themselves, as was the case of the hair on the head, when any one was placed on an insulating stool. He applied his knuckle to the key, and received an unmistakable spark. As the story is generally told, with occasionally slight contradictions, he applied his knuckle again and again to the key with a similar result. He charged a Leyden jar with the fluid and both he and his son took a shock. He then drew in his kite, packed up his apparatus and returned to his laboratory probably the most exultant and happy man in this wide world.