Benjamin Franklin letter
to Peter Collinson - July 28, 1747

This Benjamin Franklin letter is from a series of letters he wrote about his studies in electricity to his friend Peter Collinson in London. Collinson was a member of the Royal Society, a group that promoted the study of the sciences. Collinson put five of Franklin's letters together in a book called "Experiments and Observations on Electricity Made at Philadelphia in America". This book was so popular that it became the most reprinted book of the 18th century and made Franklin a household name throughout Europe.

In later versions of the book, various others of Franklin's letters were added with even more detail. In this particular letter, Franklin explains several experiments which show how electricity passes into and out of various objects, including in which he draws an electric spark from the gold gilded pages of a book. You can read the other letters in the series by going to our Benjamin Franklin and Electricity letters page.

Benjamin Franklin letter about Electricity
to Peter Collinson

(This letter refers to several drawings that Franklin sent to Collinson, the drawings can be seen here)

Philada. July 28. 1747


The inclosed is a Copy of my last, which went by the Governour's Vessel: since which we have received, by Mesnard and Ouchterlony, Hill's Theophrastus, Pemberton's Dispensatory, Wilson's Electricity and some other Pamphlets. The Proprietor's handsome Present of a complete Electrical Apparatus &c. is also come to Hand in good Order, and is put up in the Library; but little has been done with it yet, the Weather having been excessively hot and moist ever since it arrived. The Directors have ordered his very kind Letter to be answered with the Thanks of the Company. I suppose it will be done by this Ship, if her unexpected sudden Departure does not prevent.

The necessary Trouble of copying long Letters which perhaps, when they come to your Hands, may contain Nothing new or worth your Reading, so quick is the Progress made with you in Electricity, half discourages me from writing anymore on that Subject. Yet I can not forbear adding a few Observations on Mr. Muschenbroek's wonderful Bottle. vizt.

1. The Non-electric, contained in the Bottle, differs, when electrised from a Non-electric electrised out of the Bottle in this; That the Electrical Fire of the latter is accumulated on it's Surface, and forms an Electrical Atmosphere round it, of considerable Extent; but the Electrical Fire is crouded into the Substance of the former; the Glass confining it.

2. At the same Time that the Wire and Top of the Bottle &c. is electrised positively or plus, the Bottom of the Bottle is electrised negatively or minus in exact Proportion. i.e. Whatever Quantity of Electrical Fire is thrown in at [the] Top, an equal Quantity goes out of the Bottom. To understand this, Suppose the common Quantity of Electricity in each Part of the Bottle, before the Operation begins, is equal to 20, and at every Stroke of the Tube, suppose a Quantity equal to 1 is thrown in; then after the first Stroke, the Quantity contained in the Wire and upper Part of the Bottle will be 21, in the Bottom. 19. After the second, the upper Part will have 22, the lower 18, and so on, till after 20 Strokes, the upper Part will have a Quantity of Electrical Fire equal to 40, the lower none: and then the Operation ends; for no more can be thrown into the upper Part, when no more can be driven out of the lower Part. If you attempt to throw more in, it is spued back thro' the Wire, or flies out in loud Cracks thro' the Sides of the Bottle.

3. The Equilibrium can not be restored in the Bottle by inward Communication, or Contact of the Parts; but it must be done by a Communication form'd without the Bottle, between the Top and Bottom, by some Non-electric touching both at the same Time. In which Case, if the Contact be large especially, it is restored with a Violence and Quickness inexpressible; or touching each alternately, in which Case the Equilibrium is restored by Degrees.

4. As no more Electrical Fire can be thrown into the Top of the Bottle, when all is driven out of the Bottom. So in a Bottle not yet electrised, none can be thrown into the Top, when none can get out of the Bottom; which happens either when the Bottom is too thick, or when the Bottle is placed on an Electric-per-se. Again, when the Bottle is electrised, but little of the Electrical Fire can be drawn out from the Top, by touching the Wire, unless an equal Quantity can at the same Time get in at the Bottom. Thus place an Electris'd Bottle on clean Glass or dry Wax, and you will not, by touching the Wire, get out the Fire from the Top. Place it on a Non-electric, and touch the Wire, you will get it out in a short Time; but soonest, when you form a direct Communication, as above.

So wonderfully are these two States of Electricity, the plus and minus combined and ballanced in this miraculous Bottle! situated and related to each other in a Manner that I can by no Means comprehend! If it were possible that a Bottle should in one Part contain a Quantity of Air strongly comprest, and in another Part a perfect Vacuum; We know the Equilibrium would be instantly restored within. But 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 can not be restored between them but by a Communication without! Tho' the Plenum presses violently to expand, and the hungry Vacuum seems to attract as violently in Order to be filled.

5. The Shock to the Nerves (or Convulsion rather) is occasioned by the sudden Passing of the Fire thro' the Body in its Way from the Top to the Bottom of the Bottle. The Fire takes the shortest Course, as Mr. Watson justly observes; but he was mistaken in supposing, that for a person to be shock'd a Communication with the Floor is necessary (see Sequel p. 67, 68, 69). He that holds the Bottle with one Hand, and touches the Wire with the other, will be shockt as much, tho' his Shoes be dry, or even standing on Wax, as otherwise. And on the Touch of the Wire (or of the Gun Barrel, which is the same Thing) the Fire does not proceed from the touching Finger to the Wire, as he supposes, but from the Wire to the Finger, and passes thro' the Body to the other Hand, and so into the Bottom of the Bottle. We are all obliged to that Gentleman for Publishing his ingenious Observations. It is likely he has seen these little Mistakes himself before this Time; and therefore it is hardly necessary to shew him what I write: If you should, I hope, he will excuse the Freedom I have taken; it being only in a private Letter; There is also some apparent Contradiction between his No. XLVII and LXII in the Sequel which I need not further point out.

Experiments confirming the above

Exper. I. Place an electrised Vial on Wax. A small Cork Ball suspended by a dry Silk Thread held in your Hand, and brought near to the Wire, will first be attracted and then repell'd. When in this State of Repellency, sink your Hand, that the Ball may be brought towards the Bottom of the Bottle, it will there be instantly and strongly attracted, 'till it has parted with it's Fire. If the Bottle had an Electrical Atmosphere as well as the Wire, an Electrified Cork would be repell'd from one as well as from the other.

Exper. II [fig. 1]. From a bent Wire [(a)] sticking in the Table, let a small Linen Thread [(b)] hang down within half an Inch of the Electrised Vial [(c)]. Touch the Wire of the Vial repeatedly with your Finger; and at every touch you will see the Thread instantly attracted by the Bottle. This is best done with a Vinegar Cruet, or some such belly'd Bottle. As soon as you draw any Fire out from the upper Part, by touching the Wire, the lower Part of the Bottle draws an equal Quantity in by the Thread.

Exper. III [fig. 2]. Fix a Wire in the Lead, with which the Bottom of the Bottle is armed [(d)], so as that bending upwards, it's Ring End may be level with the Top, or Ring End of the Wire in the Cork [(e)], and at 3 or 4 Inches Distance. Then electrise the Bottle, and place it on Wax. If a Cork suspended by a Silk Thread [(f)] hang between these two Wires, it will play incessantly from one to the other, 'till the Bottle is no longer electrised. That is, it fetches and carries Fire from the Top to the Bottom of the Bottle till the Equilibrium is restored.

Exper. IV [fig. 3]. Place in electricised Vial upon Wax. Take a Wire [(g)] bent in the Form of a C, the Ends at such a Distance when bent, as that the upper may touch the Wire of the Bottle, when the lower touches the bottom; stick the outer Part to a Piece of Sealing Wax [(h)] which will serve as a Handle. Then apply the lower End to the Bottom of the Bottle, and gradually bring the upper End near the Wire in the Cork: the Consequence is; Spark follows Spark till the Equilibrium is restored. Touch the Top first, and on approaching the Bottom with the other End, you have a constant Stream of Fire from the Wire entering the Bottle. Touch Top and Bottom together, and the Equilibrium will soon be restored but silently and imperceptibly, the Contact being small; the crooked Wire forming the Communication.

Exper. V [fig. 4]. Let a Ring of thin Lead or Paper surround the Bottle [(i)], even at some Distance from or above the Bottom: From that Ring let a Wire proceed up till it touch the Wire of the Cork [(k)]. A Bottle, so fixt, can not by any Means be electrised; the Equilibrium is never destroyed. For while the Communication between the upper and lower Parts of the Bottle is continu'd by the outside Wire what is driven out at Bottom is constantly supplied from the Top. Hence a Bottle can not be electrised that is foul or moist on the Outside.

Exper. VI. Place a Man on a Cake of Wax and present him the Wire of the Electrified Vial to touch, you standing on the Floor, and holding it in your Hand. As often as he touches [it] he will be electrified plus, and any one standing on the Floor may draw a Spark from him. The Fire in this Experiment passes out of the Wire into him; and at the same Time out of your Hand into the Bottom of the Bottle.

Exper. VII. Give him the electrified Vial to hold, and do you touch the Wire. As often as you touch it, he will be electrified minus, and may draw a Spark from any one standing on the Floor. The Fire now Passes from the Wire to you, and from him into the Bottom of the Bottle.

Exper. VIII. Lay two Books on two Glasses back towards back, 2 or 3 Inches distant, set the electrified Vial on one, and then touch the Wire; that Book will be electrified minus; the Electrical Fire being drawn out of it by the Bottom of the Bottle. Take off the Bottle, and holding it in your Hand, touch the other Book with the Wire; that Book will be electrified plus; the Fire passing into it from the Wire, and the Bottle at the same Time supplied from your Hand. A suspended small Cork Ball will play between these Books, 'till the Equilibrium is restored.

Exper. IX. When a Body is electrised plus it will repel an electrified Feather or small Cork Ball. When minus (or when in [the] common State) it will attract them; but stronger when minus than when in the Common State, the Difference being greater.

Exper. X. Tho' as in Expert. VI. a Man standing on Wax may be electrised a Number of Times by repeatedly touching the Wire of an electrised Bottle held in the Hand of one standing on the Floor, he receiving the Fire from the Wire each Time; yet holding it in his own Hand, and touching the Wire, tho' he draws a Strong Spark, and is violently shockt, no Electricity remains in him; the Fire only passing thro' him from the upper to the lower Part of the Bottle. Observe, before the Shock, to let some one on the Floor touch him, to restore the Equilibrium in his Body; for in taking hold of the Bottom of the Bottle, he sometimes becomes a little electrised minus, which will continue after the Shock, as would also any plus Electricity he might have given him before the Shock. For, restoring an Equilibrium in the Bottle, does not at all effect the Electricity in the Man thro' whom the Fire passes: that Electricity is neither increased nor diminished.

Exper. XI. The Passing of the Electrical Fire from the upper to the lower Part of the Bottle to restore the Equilibrium, is rendered strongly visible by the following pretty Experiment. Take a Book, whose Cover is filletted with Gold; bend a Wire of 8 or 10 Inches long in this Form, slip it on the End of the Cover of the Book, over the Gold line, so as that the Shoulder of it may press on one End of the Gold Line, the Ring up, but leaning towards the other End of the Book. Lay the Book on [a] Glass or Wax; and on the other End of the Gold Line set the Bottle electrised. Then bend the springing Wire, by pressing it with a Stick of Wax, 'till it's Ring approaches the Ring of the Bottle Wire: instantly there is a strong Spark and Stroke, and the whole Line of Gold, which completes the Communication between the Top and bottom of the Bottle, will appear a vivid Flame, like the sharpest Lightning. The closer the Contact between the Shoulder of the Wire and the Gold at one End of the Line, and between the bottom of the Bottle and the Gold at the other End, the better the Experiment succeeds. The Room should be darkned. If you would have the whole Filleting round the Cover appear in Fire at once, let the Bottle and Wire touch the Gold in the diagonally opposite Corners.

The rest of this Letter on private Affairs.

To Peter Collinson Esqr. F. R. S. London

Red stars

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