Electricity
In early 1746 the study of electricity was sweeping through
Europe. European scientists had determined there were two kinds of
electricity: vitreous, which was produced by rubbing glass with silk,
and resinous, produced on resin rubbed with wool or fur.
In January of 1746, Pieter van Musschenbroek at Leyden discovered the
electric bottle, later known as the Leyden jar. This, the first
condenser of electricity, was the basis for much of early research
in electricity.
It is believed that Franklin, through correspondence with friends in
Europe, learned of these discoveries during the summer of 1746; and in
the Fall and Winter of that year proceeded to conduct his own
electrical experiments. By March of 1747 he developed some fundamental
conjectures about electricity. Two of which, on July eleventh, he wrote
at length about.
He conceived of electricity as a single fluid and substituted the words positive and negative (plus or minus) for the words vitreous and resinous. This terminology is still with us today.He also discovered "the wonderful effect of pointed bodies, both in drawing off and throwing off the electrical fire"1
For the next year Franklin was kept busy with public affairs. In particular, he was actively involved with the defense of Pennsylvania and the other colonies against the French and Indians. However, by Winter of 1748 he was able to resume his experiments with electricity. In April of 1749 he wrote to a friend and told of making for the first time in history
"what we called an electrical battery, consisting of eleven panes of large sash-glass, armed with thin leaden plates pasted on each side, placed vertically and supported at two inches distance on silk cords, with thick hooks of leaden wire, one from each side, standing upright, distant from each other, and convenient communications of wire and chain from the giving side of one pane to the receiving side of the other; that so the whole might be charged together and with the same labour as one single pane."Franklin's next major contributions involved lightning and electricity. In November of 1749 Franklin listed areas of commonality of these two, at the time separate, phenomenon.
- Giving light
- Colour of the light
- Crooked direction
- Swift motion
- Being conducted by metals
- Crack or noise in exploding
- Subsisting in water or ice
- Rending bodies it passes through
- Destroying animals
- Melting metals
- Firing inflammable substances
- Sulphureous smell
- The electrical fluid is attracted by points
"There is something, however, in the experiments of points, sending off or drawing on the electrical fire, which has not been fully explained, and which I intend to supply in my next. For the doctrine of points is very curious, and the effects of them truly wonderful; and, from what I have observed on experiments, I am of opinion that houses, ships, and even towers and churches may be effectually secured from the strokes of lightning by their means; for if, instead of the round balls of wood or metal which are commonly placed on the tops of weathercocks, vanes, or spindles of churches, spires, or masts, there should be a rod of iron eight or ten feet in length, sharpened gradually to a point like a needle, and gilt to prevent rusting, or divided into a number of points, which would be better, the electrical fire would, I think, be drawn out of a cloud silently, before it could come near enough to strike; and a light would be seen at the point, like the sailors' corpuzante [corposant: St. Elmo's fire]. This may seem whimsical, but let it pass for the present until I send the experiments at large."Franklin wrote, sometime in early 1750 to his friend Collinson, the following proposition. That is, that clouds formed over the ocean had more electricity in them than clouds formed over the land, and then when they came close enough together their different charges were equalized by the passage of lightning between them.
"If two gun barrels electrified will strike at two inches' distance, and make a loud snap, to what a great distance may 10,000 acres of electrified cloud strike and give its fire, and how loud must be that crack?"Franklin soon refined his thoughts on lightning rods and added to their design a wire which would run from the rod down the side of the building into the ground, or down round one of the shrouds of a shop and down her side till it reached the water.When clouds come close to the earth their electricity was discharged through "high hills and high trees, lofty towers, spires, masts of ships, chimneys, etc., as so many prominencies and points."3
Franklin next proposed an experiment to determine if clouds were truly electrified. This proposal he sent to the Royal Society through Collinson.
On the top of some high tower or steeple place a kind of sentry box ... big enough to contain a man and an electrical stand [an insulator]. From the middle of the stand let an iron rod rise and pass bending out of the door, and then upright twenty or thirty feet, pointed very sharp at the end. If the electrical stand be kept clean and dry, a man standing on it when such clouds are passing low might be electrified and afford sparks, the rod drawing fire to him from a cloud. If any danger to the man should be apprehended (though I think there would be none), let him stand on the floor of his box and now and then bring near to the rod the loop of a wire that has one end fastened to the leads, he holding it by a wax handle; so the sparks, if the rod is electrified, will strike from the rod to the wire and not affect him."The English Royal Society was not overly excited about Franklin's proposal when it was read to them. The French, however, were more hospitable to this new idea. A translation of Franklin's proposal made its way into the hands of three Frenchmen: Buffon, then keeper of the Jardin du Roi, Thomas-François D'Alibard, and M. de Lor, master of experimental philosophy. D'Alibard was first to be successful.
In a garden at Marley, six leagues from Paris, he set up an iron rod, an inch through and forty feet long, pointed with brass. Having no cake of resin with which to insulate it from the ground, he used a stool which was merely a squared plank with three wine bottles for legs. At twenty minutes past two on the afternoon of 10 May 1752, there was a single clap of thunder followed by hail. D'Alibard was absent, but a former dragoon named Coiffier, left to watch the experiment, heard the thunder and hurried to the rod with an electric phial. Sparks came from the iron with a crackling sound. Coiffier sent for the pryor, Raulet, of Marley. Raulet drew off all the electric fire; sat down and wrote a letter which Coiffier took to D'Alibard, who three days later made his report to the Académie Royale des Sciences.There is one more interesting aspect to Franklin's conquest of lightning. During the summer of 1752, before he know of the successful experiments which were being performed in England and other parts of Europe, Franklin conceived the idea of using a silk kite with a thread attached to it.Franklin's idea was no longer a conjecture.
The kite being raised, a considerable time elapsed before there was any appearance of its being electrified. One very promising cloud had passed over it without any effect; when, at length, just as he was beginning to despair of his contrivance, he observed some loose threads of the hempen string to stand erect, and to avoid one another, just as if they had been suspended on a common conductor. Struck with this promising appearance, he immediately presented his knuckle to the key, and the discovery was complete. He perceived a very evident electric spark.4For a humorous version of Franklin's electrical experiments with electricity see the book "Ben and Me" by Robert Lawson.
An interesting pictorial version of Franklin's kite experiment is
depicted below:
In summary, Franklin's work on electricity had enormous significance;
it changed the way we thought of the phenomenon (realizing there were
not two different types of electricity), the way we viewed one of nature's
most powerful natural phenomenon (no longer a weapon of the
Gods), and we became able to minimize the damage caused by lightning
strikes.
In 1784 Franklin was 78 years old and our minister to France. He was
at that time in his life were he always wore glasses. By August 1784
he could not without them, "distinguish a letter even of large
print." Before that year he had used
The picture below is Franklin's model of the "Pennsylvania fireplace".
Franklin's stove, as can be seen from the picture, was designed to fit
inside a fireplace. It had many advantages over the traditional
methods of heating and cooking. Because of its design it consumed
about one-fourth the amount of wood and generated a lot more heat. It
also permitted one to reduce the amount of air flow, which helped to
eliminate cold and windy drafts.
Franklin did not patent his stove, but rather gave the idea freely in
order to help his countrymen. He was not directly involved in the
manufacture of the stove, but did help his friend Robert Grace market
the stoves Grace made on Franklin's model by writing a pamphlet about
the stove.
In 1743, the same year he proposed the American Philosophical Society,
Franklin made an important meteorological observation. The following
is his observation.6
He built bulkheads not just for ships of the sea, he built
bulkheads for his countrymen for all time.
"two pair of spectacles which I shifted occasionally, as in travelling
I sometimes read and often wanted to regard the prospects. Finding
this change troublesome and not always sufficiently ready, I had the
glasses cut and half of each kind associated in the same circle."5
Franklin had invented bifocals. This idea was further improved in
1884, 100 years later, when the separate pieces of glass were cemented
together. Fused and one piece types followed in 1908 and 1910
respectively.
"We were to have an eclipse of the moon at Philadelphia, on a Friday
evening [21 October] about nine o'clock. I intended to observe it, but
was prevented by a north-east storm which came on about seven with
thick clouds, as usual, that quite obscured the whole hemisphere. Yet
when the post brought us the Boston newspaper, giving an account of
the effects of the same storm in those parts, I found the beginning of
the eclipse had been well observed there, though Boston lies
north-east of Philadelphia about four hundred miles. This puzzled me,
because the storm began with us so soon as to prevent any observation;
and being a north-east storm, I imagined it must have begun rather
sooner in places farther to the north-eastward than it did at
Philadelphia. I therefore mentioned it in a letter to my brother who
lived at Boston; and he informed me that the storm did not begin with
them till near eleven o'clock, so that they had a good observation of
the eclipse. And upon comparing all the other accounts I received from
the several colonies, of the time of beginning of the same storm ... I
found the beginning to be always later the farther north-eastward..
This observation and theory of Franklin's is truly a wonderful
accomplishment. He observed a phenomenon, thought of an explanation
that was global in size, and then gave a simple explanation of the effect.
From thence I formed an idea of the cause of these storms, which I
would explain by a familiar instance or two. Suppose a long canal of
water stopped at the end by a gate. The water is quite at rest till
the gate is open, then it begins to move out through the gate; the
water next the gate is first in motion, and moves towards the gate; the
water next to the first water moves next, and so on successively till
the water at the head of the canal is in motion, which is last of
all. In his case all the water moves indeed towards the gate, but the
successive times of beginning motion are the contrary way, viz., from
the gate gackwards to the head of the canal. Again, suppose the air in
a chamber at rest, no current through the room till you make a fire in
the chimney. Immediately the air in the chimney, being rarefied by
the fire, rises; the air next the chimney flows in to supply its
place, moving towards the chimney; and in consequence the rest of the
air successively, quite back to the door. Thus to produce our
north-east storms I suppose some great heat and rarefaction of the air
in or about the Gulf of Mexico; the air thence rising has its place
supplied by the next more northern, cooler, and therefore denser and
heavier air; that, being in motion, is followed by the next more
northern air, etc., etc., in a successive current, to which current
our coast and inland ridge of mountains give the direction of
north-east, as they lie north-east and south-west.
Franklin made many other contributions to his society, some of which
are:
