Benjamin Franklin Papers

From Benjamin Franklin to Cadwallader Colden, 23 April 1752

To Cadwallader Colden

ALS: New-York Historical Society; also draft: American Philosophical Society1

Philada. April 23. 1752


In considering your Favour of the 16th. past,2 I recollected my having wrote you Answers to some Queries concerning the Difference between Electrics per se, and Non Electrics, and the Effects of Air in Electrical Experiments, which I apprehend you may not have received. The Date I have forgot.3

We have been us’d to call those Bodies Electrics per se, which would not conduct the Electric Fluid: We once imagin’d that only such Bodies contain’d that Fluid; afterwards, that they contain’d none of it:4 But farther Experiments shew’d our Mistakes. It is to be found in all Matter we know of: And the Distinction of Electrics per se, and Non Electrics, should now be dropt as improper; and that of Conductors and Nonconductors assum’d in its Place, as I mention’d in those Answers.

I do not remember any Experiments by which it appear’d that high rectified Spirit will not conduct; perhaps you have made such. This I know, that Wax, Rosin, Brimstone, and even Glass, commonly reputed Electrics per se, will, when in a Fluid State, conduct pretty well; Glass will do it when only red hot. So that my former Position, that only Metals and Water were Conductors, and other Bodies more or less such as they partook of Metall or Moisture, was too general.

Your Conception of the Electric Fluid, that it is incomparably more subtil than Air, is undoubtedly just. It pervades dense Matter with the greatest Ease: But it does not seem to mix or incorporate willingly with mere Air, as it does with other Matter. It will not quit common Matter to join with Air. Air obstructs in some degree its Motion. An Electric Atmosphere cannot be communicated at so great a Distance thro’ intervening Air, by far, as thro’ a Vacuum. Who knows then, but there may be, as the Antients thought, a Region of this Fire,5 above our Atmosphere, prevented by our Air and its own too great Distance for Attraction, from joining our Earth? Perhaps where the Atmosphere is rarest, this Fluid may be densest; and nearer the Earth, where the Atmosphere grows denser, this Fluid may be rarer, yet some of it be low enough to attach itself to our highest Clouds, and thence they becoming electrified may be attracted by and descend towards the Earth, and discharge their Watry Contents together with that Etherial Fire. Perhaps the Aurorae Boreales are Currents of this Fluid in its own Region above our Atmosphere, becoming from their Motion visible. There is no End to Conjectures. As yet we are but Novices in this Branch of Natural Knowledge.

You mention several Differences of Salts in your Electrical Experiments. Were they all equally dry? Salt is apt to acquire Moisture from a moist Air, and some Sorts more than others. When perfectly dry’d, by lying before a Fire, or on a Stove, none that I have try’d will conduct, any better than so much Glass.

New Flannel, if dry and warm, will draw the Electric Fluid from Non Electrics, as well as that which has been worn.

I wish you had the Convenience of trying the Experiments you seem to have such Expectations from, upon various kinds of Spirits, Salts, Earths, &c. Frequently, in a Variety of Experiments, tho’ we miss what we expected to find, yet something valuable turns out, something surprizing, and instructing tho’ unthought of.

I am glad your Piece on the Principles of Action in Matter, with the Explanations, is likely soon to appear.6 I hope it may be printed correctly. Tracts on uncommon Subjects, when the Author is at a Distance, frequently suffer much in the Press, thro’ the Ignorance of the Workmen. I think my Letters were almost as fairly wrote as Print itself, yet they were publish’d with several Errata that render particular Parts quite unintelligible.7

I thank you for communicating the Illustration of the Theorem concerning Light. It is very curious. But I must own that I am much in the Dark about Light. I am not satisfy’d with the Doctrine that supposes Particles of Matter call’d 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 24 pounder discharg’d from a Cannon? Must not the Sun diminish exceedingly by such a Waste of Matter, and the Planets instead of drawing nearer to him, as some have feared, recede to greater Distances thro’ the lessened Attraction? Yet these Particles with this amazing Motion, will not drive before them or remove the least and lightest Dust they meet with: And the Sun, for aught we know, continues of his ancient Dimensions, and his Attendants move in their ancient Orbits.

May not all the Phaenomena of Light be more conveniently solved, by supposing Universal Space filled with a subtle elastic Fluid, which when at rest is not visible, but whose Vibrations affect that fine Sense 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 strait 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 farther; yet this is Light without Fuel, and I am persuaded no Part of the Electric 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 Vibration of the above-suppos’d8 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 7 different Sounds in Music, analagous to the 7 Colours, yet the Medium, Air, is the same.

If the Sun is not wasted by Expence of Light, I can easily conceive that he shall otherwise always retain the same Quantity of Matter, tho’ we should suppose him made of Sulphur constantly flaming. The Action of Fire only separates the Particles of Matter, it does not annihilate them. Water by Heat rais’d in Vapour, returns to the Earth in Rain. And if we could collect all the Particles of burning Matter that go off in Smoke, perhaps they might, with the Ashes, weigh as much as the Body before it was fired; and if we could put them into the same Position with regard to each other, the Mass would be the same as before, and might be burnt over again. The Chymists have analys’d Sulphur, and find it compos’d in certain Proportions, of Oil, Salt, and Earth: And having by the Analysis discover’d those Proportions, they can of those Ingredients make Sulphur. So we have only to suppose, that the Parts of the Sun’s Sulphur, separated by Fire, rise into his Atmosphere, there, being freed from the immediate Action of the Fire, they collect into cloudy Masses, and growing by Degrees too heavy to be longer supported, they descend to the Sun, and are burnt over again. Hence the Spots appearing on his Face, which are observ’d to diminish daily in Size, their consuming Edges being of particular Brightness.

’Tis well we are not, as poor Galileo was, subject to the Inquisition for Philosophical Heresy. My Whispers against the orthodox Doctrine in private Letters, would be dangerous; your Writing and Printing would be highly criminal. As it is, you must expect some Censure, but one Heretic will surely excuse another.

I am heartily glad to hear more Instances of the Success of the Poke Weed, in the Cure of that horrible Evil to the human Body, a Cancer. You will deserve highly of Mankind for the Communication.9 But I find in Boston they are at a Loss to know the right Plant, some asserting it is what they call Mechoacan, others other Things.1 In one of their late Papers,2 it is publickly requested that a perfect Description may be given of the Plant, its Places of Growth, &c. I have mislaid the Paper, or would send it to you. I tho’t you had describ’d it pretty fully.

With great Respect and Esteem, I am, Dear Sir, Your obliged humble Servant

B Franklin

[Note numbering follows the Franklin Papers source.]

1Letter XXIII in 1769 and 1774 editions of Exper. and Obser. It was read in the Royal Society, Nov. 11, 1756.

2See above, p. 278.

3See above, p. 201.

4Added in printed editions: “and only educed it from other bodies.”

5BF continued to speculate on the “Sphere of Fire.” See his “Loose Thoughts on a Universal Fluid,” June 25, 1784.

6See above, pp. 279–80.

7This paragraph omitted from printed editions.

8In printed editions: “above-suppos’d” replaced by “above-mentioned.”

9See above, p. 280.

1Mechoacan: bindweed. Precisely what the New Englanders had in mind is not clear, as the term covered several species. Kalm (Travels, I, 104) gave instances of the therapeutic use of pokeweed (Phytolacca americana).

2Not identified.

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