Benjamin Franklin Papers

From Benjamin Franklin to Jared Eliot, 3 May 1753

To Jared Eliot

ALS: Yale University Library; also draft: American Philosophical Society9

Philada. May 3. 1753.

Dear Sir,

I received your Essay last Post, and my Presses being at present engag’d in some publick Work that will not admit of Delay, I have engag’d Mr. Parker to print it out of hand at New York. You may expect to see it done in two or three Weeks. The Pacquet was not seal’d, and I observ’d that the Tables showing the Culture of sundry Fields were not with the rest of Mr. Jackson’s Papers. Perhaps you did not design them for the Press.1

I wish the Barbary Barley may grow. I have some of it, and have sow’d it; but it seem’d to me to have been cut too green. I have formerly heard it reckon’d the finest Barley in the World, and that it makes a great Part of the Food of the Inhabitants.2

I think I have never been more hurried in Business than at present; yet I will steal a few Minutes, to make an Observation or two on Mr. Todd’s Ingenious Letter to you.3

1. The Supposing a mutual Attraction between the Particles of Water and Air, does not seem to me to be introducing4 a new Law of Nature; such Attractions taking Place in many other known Instances.

2. Water is specifically 850 Times heavier than Air. To render a Bubble of Water then specifically lighter than Air, it seems to me that it must take up more than 850 times the Space it did before it form’d the Bubble; and within the Bubble should be either a Vacuum or Air rarified more than 850 times. If a Vacuum, would not the Bubble be immediately crush’d by the Weight of the Atmosphere? And no Heat we know of will rarify the Air any thing near so much; much less the common Heat of the Sun, or that of Friction by the Dashing on the Surface of the Water. Besides, Water agitated ever so violently produces no Heat, as has been found by accurate Experiments.

3. A hollow Sphere of Lead, has a Firmness and Consistency in it, that a hollow Sphere of fluid unfrozen Water cannot be suppos’d to have. The Lead may support the Pressure of the Water ’tis immerg’d in, but the Bubble could not support the Pressure of the Air if empty within.

4. Was ever a visible Bubble seen to rise in Air? I have made many when a Boy with Soap Suds and a Tobacco Pipe; but they all descended when loose from the Pipe, tho’ slowly, the Air impeding their Motion. They may indeed be forc’d up by a Wind from below, but do not rise of themselves, tho’ filled with warm Breath.

5. The Objection relating to our Breathing moist Air, seems weighty, and must be farther consider’d. The Air that has been breath’d has doubtless acquir’d an Addition of the perspirable Matter, which Nature intends to free the Body from, and which would be pernicious if retain’d, or return’d into the Blood. Such Air then may become unfit for Respiration, as well for that Reason, as on Account of its Moisture. Yet I should be glad to learn by some accurate Experiment whether a Draft of Air two or three times inspired and exspired, (perhaps in a Bladder) has or has not acquired more Moisture than our common Air in the dampest Weather.

As to the Precipitation of Water in the Air we breathe, perhaps it is not always a Mark of that Air’s being overloaded. In the Region of the Clouds, indeed, the Air must be overloaded (its Coldness considered) if it lets fall its Water in Drops, which we call Rain; but those Drops may fall thro’ a dryer Air near the Earth; and accordingly we find, that the Hygroscope sometimes shows a less Degree of Moisture during a Shower, than at other times when it does not rain at all. The dewy Dampness that settles on the Insides of our Walls and on our Wainscots, seems more certainly to denote an Air overloaded with Moisture, and yet this is no sure Sign. For after a long-continu’d cold Season, if the Air grow suddenly warm, the Walls, &c. continuing their Coldness longer, will for some time condense the Moisture of such Air, ’till they grow equally warm; and then they condense no more, altho’ the Air is not become dryer. And on the other Hand after a warm Spell, if the Air grow cold, tho’ moister than before, the Dew is not so apt to gather on the warm Walls. A Tankard of cold Water, will, in a hot and dry Summer’s Day, collect a Dew on its Outside. Tankard of hot Water will collect none in the moistest Weather.

6. ’Tis, I think, a Mistake, that the Trade Winds blow only in the Afternoon. They blow all Day, and all Night; and all the Year round, except in some particular Places. The Southerly Sea Breezes on your Coast indeed blow chiefly in the Afternoon. In the very long Run from the West Side of America to Guam among the Philippine Islands, Ships seldom have occasion to hand their Sails,5 and yet they make it in about 60 Days, which could not be if the Wind blew only in the Afternoon.

7. That really is, which the Gentleman justly supposes ought to be on my Hypothesis. In Sailing southward, when you first enter the Trade Wind, you find it N.E. or thereabouts, and it gradually grows more East as you approach the Line. The same Observation is made of its changing from S. East to East gradually, as you come from the Southern Latitudes to the Equator.

I have not yet had Time to transcribe my Paper on the Increase of Mankind, but hope to do it shortly, and shall be glad of your and Mr. Todd’s Sentiments on it. My Respects to that Gentleman; and be assured that I am, very affectionately, Dear Sir, Your most humble Servant

B Franklin

Mr. Elliot

[Note numbering follows the Franklin Papers source.]

9Except for the first three and the last paragraphs, this letter was read in the Royal Society, Nov. 4, 1756, and printed in 1769 Exper. and Obser., pp. 251–4.

1Eliot’s fourth Essay, containing an account of recent agricultural improvements in Norfolk by Richard Jackson, did not appear until late in the year because James Parker, like BF, was “employed in the Service of the Government.” Essays, 1934 edit., p. 76. With some revisions Jackson’s letter appeared in Gent. Mag., XXII (1752), 453–5, 501–4. The tables Eliot omitted are printed on p. 501.

2See above, p. 412.

3See above, p. 451, where Jonathan Todd discussed BF’s Physical and Meteorological Observations, 1751, above, pp. 235–43.

4In 1769 and 1774 editions of Exper. and Obser.: “is not introducing.”

5The 1769 and 1774 editions of Exper. and Obser. add: “so equal and steady is the gale.”

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