Chapter IV: Introduction (3)

It was on a visit to Boston in 1746 that Franklin met with Dr. Spence, a Scotchman, who exhibited some electrical experiments. Soon after his return to Philadelphia the tube arrived from Mr. Collinson, and Franklin acquired considerable dexterity in its use. His house was continually full of visitors, who came to see the experiments, and, to relieve the pressure upon his time, he had a number of similar tubes blown at the glass-house, and these he distributed to his friends, so that there were soon a number of "performers" in Philadelphia. One of these was Mr. Kinnersley, who, having no other employment, was induced by Franklin to become an itinerant lecturer. Franklin drew up a scheme for the lectures, and Kinnersley obtained several well-constructed instruments from Franklin's rough and home-made models. Kinnersley and Franklin appear to have worked together a good deal, and when Kinnersley was travelling on his lecture tour, each communicated to the other the results of his experiments. Franklin sent his papers to Mr. Collinson, who presented them to the Royal Society, but they were not at first judged worthy of a place in the "Transactions." The paper on the identity of lightning and electricity was sent to Dr. Mitchell, who read it before the Royal Society, when it "was laughed at by the connoisseurs." The papers were subsequently published in a pamphlet, but did not at first receive much attention in England. On the recommendation of Count de Buffon, they were translated into French. The Abbe Nollet, who had previously published a theory of his own respecting electricity, wrote and published a volume of letters defending his theory, and denying the accuracy of some of Franklin's experimental results. To these letters Franklin made no reply, but they were answered by M. le Roy. M. de Lor undertook to repeat in Paris all Franklin's experiments, and they were performed before the king and court. Not content with the experiments which Franklin had actually performed, he tried those which had been only suggested, and so was the first to obtain electricity from the clouds by means of the pointed rod. This experiment produced a great sensation everywhere, and was afterwards repeated by Franklin at Philadelphia. Franklin's papers were translated into Italian, German, and Latin; his theory met with all but universal acceptance, and great surprise was expressed that his papers had excited so little interest in England. Dr. Watson then drew up a summary of all Franklin's papers, and this was published in the "Philosophical Transactions;" Mr. Canton verified the experiment of procuring electricity from the clouds by means of a pointed rod, and the Royal Society awarded to Franklin the Copley Medal for 1753, which was conveyed to him by Governor Denny.

We must now give a short account of Franklin's contributions to electrical science.

"The first is the wonderful effect of pointed bodies, both in _drawing off_ and _throwing off_ the electrical fire."

It will be observed that this statement is made in the language of the _one_-fluid theory, of which Franklin may be regarded as the author. This theory will be again referred to presently. Franklin electrified a cannon-ball so that it repelled a cork. On bringing near it the point of a bodkin, the repulsion disappeared. A blunt body had to be brought near enough for a spark to pass in order to produce the same effect. "To prove that the electrical fire is _drawn off_ by the point, if you take the blade of the bodkin out of the wooden handle, and fix it in a stick of sealing-wax, and then present it at the distance aforesaid, or if you bring it very near, no such effect follows; but sliding one finger along the wax till you touch the blade, and the ball flies to the shot immediately. If you present the point in the dark, you will see, sometimes at a foot distance or more, a light gather upon it like that of a fire-fly or glow-worm; the less sharp the point, the nearer you must bring it to observe the light; and at whatever distance you see the light, you may draw off the electrical fire, and destroy the repelling."

By laying a needle upon the shot, Franklin showed "that points will _throw off_ as well as _draw off_ the electrical fire." A candle-flame was found to be equally efficient with a sharp point in drawing off the electricity from a charged conductor. The effect of the candle-flame Franklin accounted for by supposing the particles separated from the candle to be first "attracted and then repelled, carrying off the electric matter with them." The effect of points is a direct consequence of the law of electrical repulsion. When a conductor is electrified, the density of the electricity is greatest where the curvature is greatest. Thus, if a number of spheres are electrified from the same source, the density of the electricity on the different spheres will vary inversely as their diameters. The force tending to drive the electricity off a conductor is everywhere proportional to the density, and hence in the case of the spheres will be greatest for the smallest sphere. On this principle, the density of electricity on a perfectly sharp point, if such could exist, on a charged conductor, would be infinite and the force tending to drive it off would be infinite also. Hence a moderately sharp point is sufficient to dissipate the electricity from a highly charged conductor, or to neutralize it if the point is connected to earth and brought near the conductor so as to be electrified by induction.

Franklin next found that, if the person rubbing the electric tube stood upon a cake of resin, and the person taking the charge from the tube stood also on an insulating stand, a stronger spark would pass between these two persons than between either of them and the earth; that, after the spark had passed, neither person was electrified, though each had appeared electrified before. These experiments suggested the idea of _positive_ and _negative_ electrification; and Franklin, regarding the electric fluid as corresponding to positive electrification, remarked that "you may circulate it as Mr. Watson has shown; you may also accumulate or subtract it upon or from any body, as you connect that body with the rubber or with the receiver, the common stock being cut off." Thus Franklin regarded electricity as a fluid, of which everything in its normal state possesses a certain amount; that, by appropriate means, some of the fluid may be removed from one body and given to another. The former is then electrified negatively, the latter positively, and all processes by which bodies are electrified consist in the removal of electricity from one body or system and giving it to another. He regarded the electric fluid as repelling itself and attracting matter. AEpinus afterwards added the supposition that matter, when devoid of electricity, is self-repulsive, and thus completed the "one-fluid theory," and accounted for the repulsion observed between negatively electrified bodies.

It had been usual to employ water for the interior armatures of Leyden jars, or phials, as they were then generally called. Franklin substituted granulated lead for the water, thereby improving the insulation by keeping the glass dry. With these phials he contrived many ingenious experiments, and imitated lightning by discharging them through the gilding of a mirror or the gold lines on the cover of a book. He found that the inner and outer armatures of his Leyden jars were oppositely electrified. "Here we have a bottle containing at the same time a _plenum_ of electrical fire and a _vacuum_ of the same fire; and yet the equilibrium cannot be restored between them but by a communication _without_! though the plenum presses violently to expand, and the hungry vacuum seems to attract as violently in order to be filled." The charging of Leyden jars by cascade, that is by insulating all the jars except the last, connecting the outer armature of the first with the inner armature of the second, and so on throughout the series, was well understood by Franklin, and he knew too that by this method the extent to which each jar could be charged from a given source varied inversely as the number of jars. The discharge of the Leyden jar by alternate contacts was also carried out by him; and he found that, if the jar is first placed on an insulating stand, it may be held by the hook (or knob) without discharging it. Franklin, in fact, appears to have known almost as much about the Leyden jar as is known to-day. He found that, when the armatures were removed from a jar, no discharge would pass between them, but when a fresh pair of armatures were supplied to the glass, the jar could be discharged. "We are of opinion that there is really no more electrical fire in the phial after what is called its _charging_ than before, nor less after its _discharging_; excepting only the small spark that might be given to and taken from the non-electric matter, if separated from the bottle, which spark may not be equal to a five-hundredth part of what is called the explosion.

"The phial will not suffer what is called a _charging_ unless as much fire can go out of it one way as is thrown in by another.

"When a bottle is charged in the common way, its _inside_ and _outside_ surfaces stand ready, the one to give fire by the hook, the other to receive it by the coating; the one is full and ready to throw out, the other empty and extremely hungry; yet, as the first will not _give out_ unless the other can at the same time _receive in_, so neither will the latter receive in unless the first can at the same time give out. When both can be done at once, it is done with inconceivable quickness and violence."

Then follows a very beautiful illustration of the condition of the glass in the Leyden jar.

"So a straight spring (though the comparison does not agree in every particular), when forcibly bent, must, to restore itself, contract that side which in the bending was extended, and extend that which was contracted; if either of these two operations be hindered, the other cannot be done.

"Glass, in like manner, has, within its substance, always the same quantity of electrical fire, and that a very great quantity in proportion to the mass of the glass, as shall be shown hereafter.

"This quantity proportioned to the glass it strongly and obstinately retains, and will have neither more nor less, though it will suffer a change to be made in its parts and situation; _i.e._ we may take away part of it from one of the sides, provided we throw an equal quantity into the other."

"The whole force of the bottle, and power of giving a shock, is in the GLASS ITSELF; the non-electrics in contact with the two surfaces serving only to _give_ and _receive_ to and from the several parts of the glass, that is, to give on one side and take away from the other."

All these statements were, as far as possible, fully substantiated by experiment. They are perfectly consistent with the views held by Cavendish and by Clerk Maxwell, and, though the phraseology is not that of the modern text-books, the statements themselves can hardly be improved upon to-day.

One of Franklin's early contrivances was an electro-motor, which was driven by the alternate electrical attraction and repulsion of leaden bullets which discharged Leyden jars by alternate contacts. Franklin concluded his account of these experiments as follows:--

Chagrined a little that we have been hitherto able to produce
nothing in this way of use to mankind, and the hot weather
coming on, when electrical experiments are not so agreeable, it
is proposed to put an end to them for this season, somewhat
humorously, in a party of pleasure, on the banks of Skuylkil.
Spirits, at the same time, are to be fired by a spark sent from
side to side through the river, without any other conductor than
the water--an experiment which we some time since performed, to
the amazement of many. A turkey is to be killed for our dinner
by the _electrical shock_, and roasted by the _electrical jack_
before a fire kindled by the _electrified bottle_, when the
healths of all the famous electricians in England, Holland,
France, and Germany, are to be drunk in _electrified bumpers_,
under the discharge of guns from the _electrical battery_.

Franklin's electrical battery consisted of eleven large panes of glass coated on each side with sheet lead. The electrified bumper was a thin tumbler nearly filled with wine and electrified as a Leyden jar, so as to give a shock through the lips.

Franklin's theory of the manner in which thunder-clouds become electrified he found to be not consistent with his subsequent experiments. In the paper which he wrote explaining this theory, however, he shows some knowledge of the effects of bringing conductors into contact in diminishing their capacity. He states that two gun-barrels electrified equally and then united, will give a spark at a greater distance than one alone. Hence he asks, "To what a great distance may ten thousand acres of electrified cloud strike and give its fire, and how loud must be that crack?

"An electrical spark, drawn from an irregular body at some distance, is scarcely ever straight, but shows crooked and waving in the air. So do the flashes of lightning, the clouds being very irregular bodies.

"As electrified clouds pass over a country, high hills and high trees, lofty towers, spires, masts of ships, chimneys, etc., as so many prominences and points, draw the electrical fire, and the whole cloud discharges there.

"Dangerous, therefore, is it to take shelter under a tree during a thunder-gust. It has been fatal to many, both men and beasts.

"It is safer to be in the open field for another reason. When the clothes are wet, if a flash in its way to the ground should strike your head, it may run in the water over the surface of your body; whereas, if your clothes were dry, it would go through the body, because the blood and other humours, containing so much water, are more ready conductors.

"Hence a wet rat cannot be killed by the exploding electrical bottle [a quart jar], while a dry rat may."

In the above quotations we see, so to speak, the germ of the lightning-rod. This was developed in a letter addressed to Mr. Collinson, and dated July 29, 1750. The following quotations will give an idea of its contents:--

"The electrical matter consists of particles extremely subtile, since it can permeate common matter, even the densest metals, with such ease and freedom as not to receive any perceptible resistance.[1]

[Footnote 1: Franklin was aware of the resistance of conductors (see p. 96).]

"If any one should doubt whether the electrical matter passes through the substance of bodies or only over and along their surfaces, a shock from an electrified large glass jar, taken through his own body, will probably convince him.

"Common matter is a kind of sponge to the electrical fluid.

"We know that the electrical fluid is _in_ common matter, because we can pump it _out_ by the globe or tube. We know that common matter has near as much as it can contain, because when we add a little more to any portion of it, the additional quantity does not enter, but forms an electrical atmosphere."

To illustrate the action of a lightning-conductor on a thunder-cloud, Franklin suspended from the ceiling a pair of scales by a twisted string so that the beam revolved. Upon the floor, in such a position that the scale-pans passed over it, he placed a blunt steel punch. The scale-pans were suspended by silk threads, and one of them electrified. When this passed over the punch it dipped towards it, and sometimes discharged into it by a spark. When a needle was placed with its point uppermost by the side of the punch, no attraction was apparent, for the needle discharged the scale-pan before it came near.

"Now, if the fire of electricity and that of lightning be the same, as I have endeavoured to show at large in a former paper ... these scales may represent electrified clouds.... The horizontal motion of the scales over the floor may represent the motion of the clouds over the earth, and the erect iron punch a hill or high building; and then we see how electrified clouds, passing over hills or high buildings at too great a height to strike, may be attracted lower till within their striking distance; and lastly, if a needle fixed on the punch, with its point upright, or even on the floor below the punch, will draw the fire from the scale silently at a much greater than the striking distance, and so prevent its descending towards the punch; or if in its course it would have come nigh enough to strike, yet, being first deprived of its fire, it cannot, and the punch is thereby secured from its stroke;--I say, if these things are so, may not the knowledge of this power of points be of use to mankind, in preserving houses, churches, ships, etc., from the stroke of the 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?"

Franklin goes on to suggest the possibility of obtaining electricity from the clouds by means of a pointed rod fixed on the top of a high building and insulated. Such a rod he afterwards erected in his own house. Another rod connected to the earth he brought within six inches of it, and, attaching a small bell to each rod, he suspended a little ball or clapper by a silk thread, so that it could strike either bell when attracted to it. On the approach of a thunder-cloud, and occasionally when no clouds were near, the bells would ring, indicating that the rod had become strongly electrified. On one occasion Franklin was disturbed by a loud noise, and, coming out of his bedroom, he found an apparently continuous and very luminous discharge taking place between the bells, forming a stream of fire about as large as a pencil.

A very pretty experiment of Franklin's was that of the _golden fish_. A small piece of gold-leaf is cut into a quadrilateral having one of its angles about 150 deg., the opposite angle about 30 deg., and the other two right angles. "If you take it by the tail, and hold it at a foot or greater horizontal distance from the prime conductor, it will, when let go, fly to it with a brisk but wavering motion, like that of an eel through the water; it will then take place under the prime conductor, at perhaps a quarter or half an inch distance, and keep a continual shaking of its tail like a fish, so that it seems animated. Turn its tail towards the prime conductor, and then it flies to your finger, and seems to nibble it. And if you hold a [pewter] plate under it at six or eight inches distance, and cease turning the globe, when the electrical atmosphere of the conductor grows small it will descend to the plate and swim back again several times with the same fish-like motion; greatly to the entertainment of spectators. By a little practice in blunting or sharpening the heads or tails of these figures, you may make them take place as desired, nearer or further from the electrified plate."

By the discharge of the battery, Franklin succeeded in melting and volatilizing gold-leaf, thin strips of tinfoil, etc. His views on the nature of light are best given in his own words.

"I am not satisfied with the doctrine that supposes particles of matter called light, continually driven off from the sun's surface, with a swiftness so prodigious! Must not the smallest particle conceivable have, with such a motion, a force exceeding that of a twenty-four pounder discharged from a cannon?... Yet these particles, with this amazing motion, will not drive before them, or remove, the least and lightest dust they meet with.

"May not all the phenomena of light be more conveniently solved by supposing universal space filled with a subtile elastic fluid, which, when at rest, is not visible, but whose vibrations affect that fine sense in the eye, as those of air do the grosser organs of the ear? We do not, in the case of sound, imagine that any sonorous particles are thrown off from a bell, for instance, and fly in straight lines to the ear; why must we believe that luminous particles leave the sun and proceed to the eye? Some diamonds, if rubbed, shine in the dark without losing any part of their matter. I can make an electrical spark as big as the flame of a candle, much brighter, and therefore visible further; yet this is without fuel; and I am persuaded no part of the electrical fluid flies off in such case to distant places, but all goes directly and is to be found in the place to which I destine it. May not different degrees of the vibration of the abovementioned universal medium occasion the appearances of different colours? I think the electric fluid is always the same; yet I find that weaker and stronger sparks differ in apparent colour, some white, blue, purple, red: the strongest, white; weak ones, red. Thus different degrees of vibration given to the air produce the seven different sounds in music, analogous to the seven colours, yet the medium, air, is the same."

Mr. Kinnersley having called Franklin's attention to the fact that a sulphur globe when rubbed produced electrification of an opposite kind from that produced by a glass globe, Franklin repeated the experiment, and noticed that the discharge from the end of a wire connected with the conductor was different in the two cases, being "long, large, and much diverging when the glass globe is used, and makes a snapping (or rattling) noise; but when the sulphur one is used it is short, small, and makes a hissing noise; and just the reverse of both happens when you hold the same wire in your hand and the globes are worked alternately.... When the brush is long, large, and much diverging, the body to which it is joined seems to be throwing the fire out; and when the contrary appears it seems to be drinking in."

On October 19, 1752, Franklin wrote to Mr. Peter Collinson as follows:--

As frequent mention is made in public papers from Europe of the
success of the Philadelphia experiment for drawing the electric
fire from clouds by means of pointed rods of iron erected on
high buildings, etc., it may be agreeable to the curious to be
informed that the same experiment has succeeded in
Philadelphia, though made in a different and more easy manner,
which is as follows:--

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
hand, is to be tied a silk ribbon, and, where the silk and twine
join, a 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 there 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.

Having, in September, 1752, erected the iron rod and bells in his own house, as previously mentioned, Franklin succeeded, in April, 1753, in charging a Leyden jar from the rod, and found its charge was negative. On June 6, however, he obtained a positive charge from a cloud. The results of his observations led him to the conclusion "_That the clouds of a thunder-gust are most commonly in a negative state of electricity, but sometimes in a positive state._"

In order to illustrate a theory respecting the electrification of clouds, Franklin placed a silver can on a wine-glass. Inside the can was placed a considerable length of chain, which could be drawn out by means of a silk thread. He electrified the can from a Leyden jar until it would receive no more electricity. Then raising the silk thread, he gradually drew the chain out of the can, and found that the greater the length of chain drawn out the greater was the charge which the jar would give to the system, and as the chain was raised, spark after spark passed from the jar to the silver can, thus showing that the capacity of the system was increased by increasing the amount of chain exposed.

In 1755 Franklin observed the effects of induction; for, having attached to his prime conductor a tassel made of damp threads and electrified the conductor, he found that the threads repelled each other and stood out. Bringing an excited glass tube near the other end of the conductor, the threads were found to diverge more, "because the atmosphere of the prime conductor is pressed by the atmosphere of the excited tube, and driven towards the end where the threads are, by which each thread acquires more atmosphere." When the excited tube was brought near the threads, they closed a little, "because the atmosphere of the glass tube repels their atmospheres, and drives part of them back on the prime conductor." A number of other experiments illustrating electrical induction were also carried out.

In writing to Dr. Living, of Charlestown, under date March 18, 1755, Franklin gave the following extracts of the minutes of his experiments as explaining the train of thought which led him to attempt to obtain electricity from the clouds:--

"_November 7, 1749._ Electrical fluid agrees with lightning in these particulars: 1. Giving light. 2. Colour of the light. 3. Crooked direction. 4. Swift motion. 5. Being conducted by metals. 6. Crack or noise in exploding. 7. Subsisting in water or ice. 8. Rending bodies it passes through. 9. Destroying animals. 10. Melting metals. 11. Firing inflammable substances. 12. Sulphureous smell. The electric fluid is attracted by points. We do not know whether this property is in lightning. But since they agree in all the particulars wherein we can already compare them, is it not probable they agree likewise in this? Let the experiment be made."

Another experiment very important in its bearing on the theory of electricity was described by Franklin in the same letter to Dr. Living. It was afterwards repeated in a much more complete form by Cavendish, who deduced from it the great law that electrical repulsion varies inversely as the square of the distance between the charges. The same experiment was repeated in other forms by Faraday, who had no means of knowing what Cavendish had done. Franklin writes:--

I electrified a silver fruit-can on an electric stand, and then
lowered into it a cork ball of about an inch in diameter,
hanging by a silk string, till the cork touched the bottom of
the can. The cork was not attracted to the inside of the can, as
it would have been to the outside, and though it touched the
bottom, yet, when drawn out, it was not found to be electrified
by that touch, as it would have been by touching the outside.
The fact is singular. You require the reason? I do not know it.
Perhaps you may discover it, and then you will be so good as to
communicate it to me. I find a frank acknowledgment of one's
ignorance is not only the easiest way to get rid of a
difficulty, but the likeliest way to obtain information, and
therefore I practise it. I think it is an honest policy.

A note appended to this letter runs as follows:--

Mr. F. has since thought that, possibly, the mutual repulsion of
the inner opposite sides of the electrized can may prevent the
accumulating an electric atmosphere upon them, and occasion it
to stand chiefly on the outside. But recommends it to the
further examination of the curious.

The explanation in this note is the correct one, and from the fact that in the case of a completely closed hollow conductor the charge is not only _chiefly_ but _wholly_ on the outside, the law of inverse squares above referred to follows as a mathematical consequence.

On writing to M. Dalibard, of Paris, on June 29, 1755, Franklin complained that, though he always (except once) assigned to lightning-rods the alternative duty of either _preventing_ a stroke or of _conducting_ the lightning with safety to the ground, yet in Europe attention was paid only to the _prevention_ of the stroke, which was only a _part_ of the duty assigned to the conductors. This is followed by the description of the effect of a stroke upon a church-steeple at Newbury, in New England. The spire was split all to pieces, so that nothing remained above the bell. The lightning then passed down a wire to the clock, then down the pendulum, without injury to the building. "From the end of the pendulum, down quite to the ground, the building was exceedingly rent and damaged, and some stones in the foundation-wall torn out and thrown to the distance of twenty or thirty feet." The pendulum-rod was uninjured, but the fine wire leading from the bell to the clock was vaporized except for about two inches at each end.

Mr. James Alexander, of New York, having proposed to Franklin that the velocity of the electric discharge might be measured by discharging a jar through a long circuit of river-water, Franklin, in his reply, explained that such an experiment, if successful, would not determine the actual velocity of electricity in the conductor. He compared the electricity in conductors to an incompressible fluid, so that when a little additional fluid is injected at one end of a conductor, an equal amount must be extruded at the other end--his view apparently being identical with that of Maxwell, who held that all electric displacements must take place _in closed circuits_.

"Suppose a tube of any length open at both ends.... If the tube be filled with water, and I inject an additional inch of water at one end, I force out an equal quantity at the other in the very same instant.

"And the water forced out at one end of the tube is not the very same water that was forced in at the other end at the same time; it was only one motion at the same time.

"The long wire, made use of in the experiment to discover the velocity of the electric fluid, is itself filled with what we call its natural quantity of that fluid, before the hook of the Leyden bottle is applied at one end of it.

"The outside of the bottle being at the time of such application in contact with the other end of the wire, the whole quantity of electric fluid contained in the wire is, probably, put in motion at once.

"For at the instant the hook, connected with the inside of the bottle, _gives out_, the coating or outside of the bottle _draws in_, a portion of that fluid....

"So that this experiment only shows the extreme facility with which the electric fluid moves in metal; it can never determine the velocity.

"And, therefore, the proposed experiment (though well imagined and very ingenious) of sending the spark round through a vast length of space, by the waters of Susquehannah, or Potowmack, and Ohio, would not afford the satisfaction desired, though we could be sure that the motion of the electric fluid would be in that tract, and not underground in the wet earth by the shortest way."

In his investigations of the source of electricity in thunder-clouds, Franklin tried an experiment which has been frequently repeated with various modifications. Having insulated a large brass plate which had been previously heated, he sprinkled water upon it, in order, if possible, to obtain electricity by the evaporation of the water, but no trace of electrification could be detected.

During his visit to England, Franklin wrote many letters to Mr. Kinnersley and others on philosophical questions, but they consisted mainly of accounts of the work done by other experimenters in England, his public business occupying too much of his attention to allow him to conduct investigations for himself. In one of his letters, speaking of Lord Charles Cavendish, he says:--

It were to be wished that this noble philosopher would
communicate more of his experiments to the world, as he makes
many, and with great accuracy.

When the controversy between the relative merits of points and knobs for the terminals of lightning-conductors arose, Franklin wrote to Mr. Kinnersley:--

Here are some electricians that recommend knobs instead of
points on the upper end of the rods, from a supposition that the
points invite the stroke. It is true that points draw
electricity at greater distances in the gradual silent way; but
knobs will draw at the greatest distance a stroke. There is an
experiment which will settle this. Take a crooked wire of the
thickness of a quill, and of such a length as that, one end of
it being applied to the lower part of a charged bottle, the
upper may be brought near the ball on the top of the wire that
is in the bottle. Let one end of this wire be furnished with a
knob, and the other may be gradually tapered to a fine point.
When the point is presented to discharge the bottle, it must be
brought much nearer before it will receive the stroke than the
knob requires to be. Points, besides, tend to repel the
fragments of an electrical cloud; knobs draw them nearer. An
experiment, which I believe I have shown you, of cotton fleece
hanging from an electrized body, shows this clearly when a point
or a knob is presented under it.

The following quotation from Franklin's paper on the method of securing buildings and persons from the effects of lightning is worthy of attention, for of late years a good deal of money has been wasted in providing insulators for lightning-rods. A few years ago the vicar and churchwardens of a Lincolnshire parish were strongly urged to go to the expense of insulating the conductor throughout the whole height of the very lofty tower and spire of their parish church. Happily they were wise enough to send the lightning-rod man about his business. But this is not the only case which has come under the writer's notice, showing that there is still a widespread impression that lightning-conductors should be carefully insulated. Franklin says:--

"The rod may be fastened to the wall, chimney, etc., with staples of iron. The lightning will not leave the rod (a good conductor) to pass into the wall (a bad conductor) through these staples. It would rather, if any were in the wall, pass out of it into the rod, to get more readily by that conductor into the earth."[2]

[Footnote 2: See p. 141.]

The conditions to be secured in a lightning-conductor are, firstly, a sharp point projecting above the highest part of the building, and gilded to prevent corrosion; secondly, metallic continuity from the point to the lower end of the conductor; and, thirdly, a good earth-contact. The last can frequently be secured by soldering the conductor to iron water-pipes underground. Where these are not available, a copper plate, two or three feet square, imbedded in clay or other damp earth, will serve the purpose. The method of securing a building which is erected on granite or other foundation affording no good earth-connection, will be referred to in a subsequent biographical sketch.

The controversy of points _versus_ knobs was again revived in London when Franklin was in Paris, and the War of Independence had begun. Franklin was consulted on the subject, the question having arisen in connection with the conductor at the palace. His reply was characteristic.

"As to my writing anything on the subject, which you seem to desire, I think it not necessary, especially as I have nothing to add to what I have already said upon it in a paper read to the committee who ordered the conductors at Purfleet, which paper is printed in the last French edition of my writings.

"I have never entered into any controversy in defence of my philosophical opinions. I leave them to take their chance in the world. If they are _right_, truth and experience will support them; if _wrong_, they ought to be refuted and rejected. Disputes are apt to sour one's temper and disturb one's quiet. I have no private interest in the reception of my inventions by the world, having never made, nor proposed to make, the least profit by any of them. The king's changing his _pointed_ conductors for _blunt_ ones is, therefore, a matter of small importance to me. If I had a wish about it, it would be that he had rejected them altogether as ineffectual. For it is only since he thought himself and family safe from the thunder of Heaven, that he dared to use his own thunder in destroying his innocent subjects."

The paper referred to was read before "the committee appointed to consider the erecting conductors to secure the magazines at Purfleet," on August 27, 1772. It described a variety of experiments clearly demonstrating the effect of points in discharging a conductor. This was a committee of the Royal Society, to whom the question had been referred on account of Dr. Wilson's recommendation of a blunt conductor. The committee decided in favour of Franklin's view, and when, in 1777, the question was again raised and again referred to a committee of the Royal Society, the decision of the former committee was confirmed, "conceiving that the experiments and reasons made and alleged to the contrary by Mr. Wilson are inconclusive."

Though Franklin's scientific reputation rests mainly on his electrical researches, he did not leave other branches of science untouched. Besides his work on atmospheric electricity, he devoted a great deal of thought to meteorology, especially to the vortical motion of waterspouts. The Gulf-stream received a share of his attention. His improvements in fireplaces have already been noticed; the cure of smoky chimneys was the subject of a long paper addressed to Dr. Ingenhousz, and of some other letters. One of his experiments on the absorption of radiant energy has been deservedly remembered.

"My experiment was this: I took a number of little square pieces of broad-cloth from a tailor's pattern-card, of various colours. There were black, deep blue, lighter blue, green, purple, red, yellow, white, and other colours or shades of colours. I laid them all out upon the snow in a bright, sun-shiny morning. In a few hours (I cannot now be exact as to the time) the black, being warmed most by the sun, was sunk so low as to be below the stroke of the sun's rays; the dark blue almost as low, the lighter blue not quite so much as the dark, the other colours less as they were lighter; and the quite white remained on the surface of the snow, not having entered it at all.

"What signifies philosophy that does not apply to some use? May we not learn from hence that black clothes are not so fit to wear in a hot, sunny climate or season, as white ones?"

Franklin knew much about electricity, but his knowledge of human nature was deeper still. This appears in all his transactions. His political economy was, perhaps, not always sound, but his judgment of men was seldom at fault.

"Finally, there seem to be but three ways for a nation to acquire wealth. The first is by _war_, as the Romans did, in plundering their conquered neighbour: this is _robbery_. The second by _commerce_, which is generally _cheating_. The third by _agriculture_, the only _honest way_, wherein man receives a real increase of the seed thrown into the ground, in a kind of continual miracle wrought by the hand of God in his favour, as a reward for his innocent life and his virtuous industry."

When Franklin reached London in 1757 he took up his abode with Mrs. Margaret Stevenson, in Craven Street, Strand. For Mrs. Stevenson and her daughter Mary, then a young lady of eighteen, he acquired a sincere affection, which continued throughout their lives. Miss Stevenson spent much of her time with an aunt in the country, and some of Franklin's letters to her respecting the conduct of her "higher education" are among the most interesting of his writings. Miss Stevenson treated him as a father, and consulted him on every question of importance in her life. When she was a widow and Franklin eighty years of age, he urged upon her to come to Philadelphia, for the sake of the better prospects which the new country offered her boys. In coming to England, Franklin brought with him his son William, who entered the Middle Temple, but he left behind his only daughter, Sarah, in charge of her mother. To his wife and daughter he frequently sent presents from London, and his letters to Mrs. Franklin give a pretty full account of all his doings while in England. During his visit he received the honorary degrees of D.C.L. from the University of Oxford, and LL.D. from that of Edinburgh. At Cambridge he was sumptuously entertained. In August, 1762, he started again for America, and reached Philadelphia on November 1, after an absence of five years. His son William had shortly before been appointed Governor of New Jersey. From this time William Franklin became very much the servant of the proprietaries and of the English Government, but no offer of patronage produced any effect on the father.

Franklin's stay in America was of short duration, but while there he was mainly instrumental in quelling an insurrection in Pennsylvania. He made a tour of inspection through the northern colonies in the summer of 1763, to regulate the post-offices. The disorder just referred to in the province caused the governor, as well as the Assembly, to determine on the formation of a militia. A committee, of which Franklin was a member, drew up the necessary bill. The governor claimed the sole power of appointing officers, and required that trials should be by court-martial, some offences being punishable with death. The Assembly refused to agree to these considerations. The ill feeling was increased by the governor insisting on taxing all proprietary lands at the same rate as uncultivated land belonging to other persons, whether the proprietary lands were cultivated or not. The Assembly, before adjourning, expressed an opinion that peace and happiness would not be secured until the government was lodged directly in the Crown. When the Assembly again met, petitions to the king came in from more than three thousand inhabitants. In the mean while the British Ministry had proposed the Stamp Act, which was similar in principle to the English Stamp Act, which requires that all agreements, receipts, bills of exchange, marriage and birth certificates, and all other legal documents should be provided with an inland revenue stamp of a particular value, in order that they might be valid. As soon as the Assembly was convened, it determined to send Franklin to England, to take charge of a petition for a change of government. The merchants subscribed L1100 towards his expenses in a few hours, and in twelve days he was on his journey, being accompanied to the ship, a distance of sixteen miles, by a cavalcade of three hundred of his friends, and in thirty days he reached London. Arrived in London, he at once took up his abode in his old lodgings with Mrs. Stevenson. He was a master of satire, equalled only by Swift, and during the quarrels which preceded the War of Independence, as well as during the war, he made good use of his powers in this respect. Articles appeared in some of the English papers tending to raise an alarm respecting the competition of the colonies with English manufacturers. Franklin's contribution to the discussion was a caricature of the English press writers.

"It is objected by superficial readers, who yet pretend to some knowledge of those countries, that such establishments [manufactories for woollen goods, etc.] are not only improbable, but impossible, for that their sheep have but little wool, not in the whole sufficient for a pair of stockings a year to each inhabitant; that, from the universal dearness of labour among them, the working of iron and other materials, except in a few coarse instances, is impracticable to any advantage.

"Dear sir, do not let us suffer ourselves to be amused with such groundless objections. The very tails of the American sheep are so laden with wool that each has a little car or waggon on four little wheels to support and keep it from trailing on the ground. Would they caulk their ships, would they even litter their horses with wool, if it were not both plenty and cheap? And what signifies the dearness of labour, when an English shilling passes for five and twenty? Their engaging three hundred silk throwsters here in one week for New York was treated as a fable, because, forsooth, they have 'no silk there to throw!' Those who make this objection perhaps do not know that, at the same time, the agents for the King of Spain were at Quebec, to contract for one thousand pieces of cannon to be made there for the fortification of Mexico, and at New York engaging the usual supply of woollen floor-carpets for their West India houses. Other agents from the Emperor of China were at Boston, treating about an exchange of raw silk for wool, to be carried in Chinese junks through the Straits of Magellan.

"And yet all this is as certainly true as the account said to be from Quebec in all the papers of last week, that the inhabitants of Canada are making preparations for a cod and whale fishery this summer in the upper Lakes. Ignorant people may object that the upper Lakes are fresh, and that cod and whales are salt-water fish; but let them know, sir, that cod, like other fish when attacked by their enemies, fly into any water where they can be safest; that whales, when they have a mind to eat cod, pursue them wherever they fly; and that the grand leap of the whale in the chase up the Falls of Niagara is esteemed, by all who have seen it, as one of the finest spectacles in nature."

One of Franklin's chief objects in coming to England was to prevent the passing of Mr. Grenville's bill, previously referred to as the Stamp Act. The colonists urged that they had always been liberal in their votes, whenever money was required by the Crown, and that taxation and representation must, in accordance with the British constitution, go hand-in-hand, so that the English Parliament had no right to raise taxes in America, so long as the colonists were unrepresented in Parliament. "Had Mr. Grenville, instead of that act, applied to the king in Council for such requisitional letters [_i.e._ requests to the Assemblies for voluntary grants], to be circulated by the Secretary of State, I am sure he would have obtained more money from the colonies by their voluntary grants than he himself expected from the sale of stamps. But he chose compulsion rather than persuasion, and would not receive from their good will what he thought he could obtain without it." The Stamp Act was passed, stamps were printed, distributors were appointed, but the colonists would have nothing to do with the stamps. The distributors were compelled to resign their commissions, and the captains of vessels were forbidden to land the stamped paper. The cost of printing and distributing amounted to L12,000; the whole return was about L1500, from Canada and the West Indies.

The passing of the Stamp Act was soon followed by a change of Ministry, when the question again came before Parliament. Franklin submitted to a long examination before a Committee of the whole House. The feeling prevalent in America respecting the Stamp Act may be inferred from some of his answers.

"31. _Q._ Do you think the people of America would submit to pay the stamp duty if it was moderated?

"_A._ No, never, unless compelled by force of arms.

"36. _Q._ What was the temper of America towards Great Britain before the year 1763?[3]

[Footnote 3: The date of the Sugar Act.]

"_A._ The best in the world. They submitted willingly to the government of the Crown, and paid, in their courts, obedience to the Acts of Parliament. Numerous as the people are in the several old provinces, they cost you nothing in forts, citadels, garrisons, or armies to keep them in subjection. They were governed by this country at the expense only of a little pen, ink, and paper; they were led by a thread. They had not only a respect, but an affection, for Great Britain--for its laws, its customs and manners, and even a fondness for its fashions, that greatly increased the commerce. Natives of Britain were always treated with particular regard; to be an _Old-Englandman_ was, of itself, a character of some respect, and gave a kind of rank among us.

"37. _Q._ And what is their temper now?

"_A._ Oh, very much altered.

"50. _Q._ Was it an opinion in America before 1763 that the Parliament had no right to lay taxes and duties there?

"_A._ I never heard any objection to the right of laying duties to regulate commerce; but a right to lay internal taxes was never supposed to be in Parliament, as we are not represented there.

"59. _Q._ You say the colonies have always submitted to external taxes, and object to the right of Parliament only in laying internal taxes; now, can you show that there is any kind of difference between the two taxes to the colony on which they may be laid?

"_A._ I think the difference is very great. An _external_ tax is a duty laid on commodities imported; that duty is added to the first cost and other charges on the commodity, and, when it is offered to sale, makes a part of the price. If the people do not like it at that price, they refuse it; they are not obliged to pay it. But an _internal_ tax is forced upon the people without their consent, if not laid by their own representatives. The Stamp Act says we shall have no commerce, make no exchange of property with each other, neither purchase, nor grant, nor recover debts; we shall neither marry nor make our wills, unless we pay such and such sums; and thus it is intended to extort our money from us, or ruin us by the consequences of refusing to pay it.

"61. _Q._ Don't you think cloth from England absolutely necessary to them?

"_A._ No, by no means absolutely necessary; with industry and good management they may very well supply themselves with all they want.

"62. _Q._ Will it not take a long time to establish that manufacture among them? and must they not in the mean while suffer greatly?

"_A._ I think not. They have made a surprising progress already. And I am of opinion that, before their old clothes are worn out, they will have new ones of their own making.