Benjamin Franklin Papers

From Benjamin Franklin to James Bowdoin, 24 January 1752

To James Bowdoin

ALS: Massachusetts Historical Society2

Philada. Jan. 24. 1752


I am glad to learn by your Favour of the 21st past,3 that Mr. Kinnersley’s Lectures have been acceptable to the Gentlemen of Boston, and are like to prove serviceable to himself. I thank you for the Countenance and Encouragement you have so kindly afforded my Fellow-Citizen.

I send you enclos’d an Extract of a Letter containing the Substance of what I observ’d concerning the Communication of Magnetism to Needles by Electricity.4 The Minutes I took at the Time of the Experiments are mislaid. I am very little acquainted with the Nature of Magnetism. Dr. Gawin Knight, Inventor of the Steel Magnets, has wrote largely on that Subject;5 but I have not yet had Leisure to peruse his Writings with the Attention necessary to become Master of his Doctrine.

Your Explication of the crooked Direction of Lightning, appears to me both ingenious and solid.6 When we can account as satisfactorily for the Electrification of Clouds, I think that Branch of Natural Philosophy will be nearly compleat.

The Air undoubtedly obstructs the Motion of the Electric Fluid. Dry Air prevents the Dissipation of an Electric Atmosphere; the denser the more, as in cold Weather. I question whether such an Atmosphere can be retained by a Body in Vacuo. A common Electrical Vial requires a Non Electric Communication from the Wire to every Part of the charg’d Glass, otherwise being dry and clean, and fill’d with Air only, it charges slowly, and discharges gradually by Sparks without a Shock: But exhausted of Air, the Communication is so open and free between the inserted Wire and Surface of the Glass, that it charges as readily, and shocks as smartly as if fill’d with Water. And I doubt not, but that, in the Experiment you propose, the Spark would not only be near strait in Vacuo, but strike at a greater Distance than in the open Air, tho’ perhaps there would not be a loud Explosion. As soon as I have a little Leisure, I will make the Experiment and send you the Result.

My Supposition that the Sea might possibly be the grand Source of Lightning, arose from the common Observation of its luminous Appearance in the Night on the least Motion; an Appearance never observ’d in fresh Water. Then I knew that the Electric Fluid may be pump’d up out of the Earth by the Friction of a Glass Globe, on a non-electric Cushion; and that notwithstanding the surprizing Activity and Swiftness of that Fluid, and the non-electric Communication between all Parts of the Cushion and the Earth, yet Quantities would be snatch’d up by the revolving Surface of the Globe, thrown on the Prime Conductor, and dissipated in Air. How this was done, and why that subtile active Spirit did not immediately return again from the Globe into some part or other of the Cushion and so into the Earth, was difficult to conceive; but whether from its being oppos’d by a Current setting upwards to the Cushion, or from whatever other Cause, that it did not so return, was an evident Fact. Then I considered the separate Particles of Water as so many hard Spherules, capable of touching the Salt only in Points, and imagined a Particle of Salt could therefore no more be wet by a Particle of Water, than a Globe by a Cushion; that there might therefore be such a Friction between the originally constituent Particles of Salt and Water (as in a Sea of Globes and Cushions) that each Particle of Water on the Surface might obtain from the common Mass some Particles of the universally-diffused much finer and more subtile electric Fluid, and forming to itself an Atmosphere of those Particles, be repell’d from the then generally electrified Surface of the Sea, and fly away with them into the Air. I thought too, that possibly the great Mixture of Particles Electric per se in the Ocean Water, might in some degree impede the swift Motion and Dissipation of the Electric Fluid thro’ it to the Shores, &c. But having since found, that Salt in the Water of a Vial does not lessen the Shock; and having endeavour’d in vain to produce that luminous Appearance from a Mixture of Salt and Water agitated; and observed that even the Sea Water will not produce it after some hours standing in a Bottle, I suspect it to proceed from some Principle yet unknown to us (which I would gladly make some Experiments to discover, if I lived near the Sea) and I grow more doubtful of my former Supposition, and more ready to allow Weight to that Objection (drawn from the Activity of the Electric Fluid, and the Readiness of Water to conduct) which you have indeed stated with great Strength and Clearness.

In the meantime, before we part with this Hypothesis, let us think what to substitute in its Place. I have sometimes queried, whether the Friction of the Particles of Air,7 an Electric per se, in violent Winds, among Trees, and against the Surface of the Earth, might not, as so many glass Globes, pump up Quantities of the Electric Fluid, which the rising Vapours might receive from the Air, and retain in the Clouds they form? on which I should be glad to have your Sentiments. An ingenious Friend of mine8 supposes the Land Clouds more likely to be electrified than the Sea Clouds: I send his Letter for your Perusal, which please to return me.

I have wrote nothing lately on Electricity, nor observ’d anything new that is material, my Time being much taken up with other Affairs. Yesterday I discharged 4 Jars thro’ a fine Wire ty’d up between two Strips of Glass: The Wire was partly melted, and the rest broke into small Pieces from half an Inch to half a Quarter of an Inch. My Globe raises the Electric Fire with greater Ease in much greater Quantities by the Means of a Wire extended from the Cushion to the Iron Pin of a Pump-handle behind my House, which communicates by the Pump-spear with the Water in the Well.

By this Post I send to Dr. Perkins, who is curious in that Way, some meteorological Observations and Conjectures,9 and desire him to communicate them to you, as they may afford you some Amusement, and I know you will look over them with a candid Eye. By throwing our occasional Thoughts on Paper, we more readily discover the Defects of our Opinions, or we digest them better, and find new Arguments to support them. This I sometimes practice, but such Pieces are fit only to be seen by Friends.

I am, with great Respect, Sir, Your most humble Servant

B Franklin

P.S. I have not time now to transcribe the abovemention’d Piece for the Dr. and must defer it to a future Opportunity.

Endorsed: Mr Benja. Franklin of Phila. Letter Janry 24. 1752, on electricity.

[Note numbering follows the Franklin Papers source.]

2Letter XIV in 1769 and 1774 editions of Exper. and Obser. Read in the Royal Society, May 27, 1756.

3See above, p. 216.

4See above, p. 143.

5Gowin Knight (see above, III, 111 n) contributed several papers on magnets and magnetism to Phil. Trans., XLIII (1744–45), 161–6, 361–3; XLIV (1746–47), 656–72; XLVI (1749–50), 113–7, 505–12, which were collected and published, 1758.

6See above, pp. 217–18.

7Omitted in 1769 and 1774 editions: “of the Particles.”

8Cadwallader Colden. See Bowdoin’s comments on his views, below, p. 277.

9See above, p. 235.

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