An Account of the Kite Experiment
From Carl Van Doren's "Benjamin Franklin," ©1938 by Carl Van Doren
Before that he had thought of another way of proving his theory, and with the help of his electrical kite had drawn lightning from a cloud. The episode of the kite, so firm and fixed in legend, turns out to be dim and mystifying in fact. Franklin himself never wrote the story of the most dramatic of his experiments. All that is known about what he did on that famous day, of no known date, comes from Joseph Priestley's account, published fifteen years afterwards but read in manuscript by Franklin, who must have given Priestley the precise, familiar details.
"As every circumstance relating to so capital a discovery (the greatest, perhaps, since the time of Sir Isaac Newton) cannot but give pleasure to all my readers, I shall endeavour to gratify them with the communication of a few particulars which I have from the best authority.
"The Doctor, having published his method of verifying his hypothesis concerning the sameness of electricity with the matter of lightning, was waiting for the erection of a spire [on Christ Church] in Philadelphia to carry his views into execution; not imagining that a pointed rod of a moderate height could answer the purpose; when it occurred to him that by means of a common kite he could have better access to the regions of thunder than by any spire whatever. Preparing, therefore, a large silk handkerchief and two cross-sticks of a proper length on which to extend it, he took the opportunity of the first approaching thunderstorm to take a walk in the fields, in which there was a shed convenient for his purpose. But, dreading the ridicule which too commonly attends unsuccessful attempts in science, he communicated his intended experiment to nobody but his son" — then twenty-one, not a child as in the traditional illustrations of the scene — "who assisted him in raising the kite.
How Franklin Made His Kite
Written by Benjamin Franklin to Peter Collinson, October 19, 1752
Make a small cross of two light strips of cedar, the arms so long as to reach to the four corners of a large thin silk handkerchief when extended; tie the corners of the handkerchief to the extremities of the cross, so you have the body of a kite; which being properly accommodated with a tail, loop, and string, will rise in the air, like those made of paper; but this being of silk is fitter to bear the wet and wind of a thunder gust without tearing. To the top of the upright stick of the cross is to be fixed a very sharp pointed wire, rising a foot or more above the wood. To the end of the twine, next the key may be fastened. This kite is to be raised when a thunder-gust appears to be coming on, and the person who holds the string must stand within a door or window, or under some cover, so that the silk ribbon may not be wet; and care must be taken that the twine does not touch the frame of the door or window. As soon as any of the thunder clouds come over the kite, the pointed wire will draw the electric fire from them, and the kite, with all the twine, will be electrified, and the loose filaments of the twine, will stand out every way, and be attracted by an approaching finger. And when the rain has wetted the kite and twine, so that it can conduct the electric fire freely, you will find it stream out plentifully from the key on the approach of your knuckle. At this key the phial may be charged: and from electric fire thus obtained, spirits may be kindled, and all the other electric experiments be performed, which are usually done by the help of a rubbed glass globe or tube, and thereby the sameness of the electric matter with that of lightning completely demonstrated.
For Whom the Bells Toll
Franklin's "iron rod" drew lightning down into his house. The rod was connected to a bell and a second bell was connected to a grounded wire. Every time there was an electrical storm, the bells would ring and sparks would illuminate his house.
Franklin described the experiment as follows. The rod was:
"fixed to the top of my chimney and extending abut nine feet above it. From the foot of this rod a wire (the thickness of a goose-quill) came through a covered glass tube in the roof and down through the well of the staircase; the lower end connected with the iron spear of a pump. On the staircase opposite to my chamber door the wire was divided; the ends separated about six inches, a little bell on each end; and between the bells a little brass ball, suspended by a silk thread, to play between and strike the bells when clouds passed with electricity in them. After having frequently drawn sparks and charged bottles from the bell of the upper wire, I was one night awakened by aloud cracks on the staircase. Starting up and opening the door, I perceived that the brass ball, instead of vibrating as usual between the bells was repelled and kept at a distance from both; while the fire passed, sometimes in very large, quick cracks from bell to bell, and sometimes in a continued, dense, white stream, seemingly as large as my finger, whereby the whole staircase was inlightened with sunshine, so that one might see to pick up a pin."
Legend has it that Franklin's wife, Deborah, was so flustered by the ringing bells and flashing lights, that she wrote to her husband who was off in London, asking him how to disconnect the experiment.
Assault on Batteries
Before Franklin started his scientific experimentation, it was thought that electricity consisted of two opposing forces. Franklin showed that electricity consisted of a "common element" which he named "electric fire." Further, electricity was "fluid" like a liquid. It passed from one body to another — however it was never destroyed. In a letter to Peter Collinson, Franklin wrote that the:
"fire only circulates. Hence have arisen some new items among us. We say B (and other Bodies alike circumstanced) are electricised positively; A negatively; Or rather B is electricised plus and A minus ... These terms we may use till philosophers give us better."
Franklin's work became the basis for the single fluid theory. When something is being charged, such as a car battery, electricity flows from a positive body, that with an excess charge, to a negative body, that with negative charge. Indeed, a car battery has plus and minus signs on its terminals.
Franklin wrote Collinson in another letter that: "I feel a Want of Terms here and doubt much whether I shall be able to make this intelligible." Not only did Franklin have to posit theories, he also had to create a new language to fit them. Some of the electrical terms which Franklin coined during his experiments include:
They are still the terms we use today.