Benjamin Franklin Papers

From Benjamin Franklin to Mary Stevenson, 10 August 1761

To Mary Stevenson

ALS: Yale University Library7

Cravenstreet, Aug. 10. 61

Dear Polley,

I received yesterday my Papers.8 I had sent for them before to Mr. Stanley’s, but Peter found no one at home. It has however been of no Damage to me, except being so long without the Pleasure of reading your agreable little Letter that accompanied them.

We are to set out this Week for Holland, where we may possibly spend a Month, but purpose to be at home again before the Coronation.9 I could not go without taking Leave of you by a Line at least, when I am so many Letters in your Debt.

In yours of May 19.1 which I have before me, you speak of the Ease with which Salt Water may be made fresh by Distillation, supposing it to be, as I had said, that in Evaporation the Air would take up Water but not the Salt that was mix’d with it. It is true that distill’d Sea Water will not be salt, but there are other disagreable Qualities that rise with the Water in Distillation; which indeed Several besides Dr. Hales2 have endeavoured by sundry Means to prevent; but as yet their Methods have not been brought much into Use. I have his Pieces on the Subject, which I will leave with your Mother for your Perusal, as you may possibly make her happy a Day or two with your Company before our Return.

I have a singular Opinion on this Subject, which I will venture to communicate to you, tho’ I doubt you will rank it among my Whims. It is certain that the Skin has imbibing as well as discharging Pores;3 witness the Effects of a Blister Plaister, etc. I have read that a Man hired by a Physician to stand by way of Experiment in the open Air naked during a moist Night, weighed near 3 Pounds heavier in the Morning. I have often observ’d myself, that however thirsty I may have been before going into the Water to swim, I am never long so in the Water. These imbibing Pores, however, are very fine, perhaps fine enough in filtring to separate Salt from Water; for tho’ I have been soak’d by swimming, when a Boy, several Hours in the Day for several Days successively in Saltwater, I never found my Blood and Juices salted by that means, so as to make me thirsty or feel a salt Taste in my Mouth: And it is remarkable that the Flesh of Sea Fish, tho’ bred in Salt Water, is not salt. Hence I imagine, that if People at Sea, distress’d by Thirst when their fresh Water is unfortunately spent, would make Bathing-Tubs of their empty Water Casks, and filling them with Sea Water, sit in them an Hour or two each Day, they might be greatly reliev’d. Perhaps keeping their Clothes constantly wet might have an almost equal Effect; and this without Danger of catching Cold. Men do not catch Cold by wet Clothes at Sea. Damp but not wet Linnen may possibly give Colds; but no one catches Cold by Bathing, and no Clothes can be wetter than Water itself. Why damp Clothes should then occasion Colds, is a curious Question, the Discussion of which I reserve for a future Letter, or some future Conversation.4

Adieu, my dear little Philosopher. Present my respectful Compliments to the good Ladies your Aunts, and to Miss Pitt; and believe me ever Your affectionate Friend and humble Servant

B Franklin

P.S. I begin to see a Rival in Dr. Hawkesworth.5 But, what is uncommon with Rivals, the more he likes you, and you him, the more, if possible, I shall esteem you both.

[Note numbering follows the Franklin Papers source.]

7Printed as Letter LII in Exper. and Obser., 1769 edit., pp. 458–60, but with the omission of the first paragraph and the postscript. Sparks, Bigelow, and Smyth all reprinted the text with these omissions.

8For these papers and Polly’s covering letter, see above, pp. 333–4.

9On BF and WF’s trip to the Netherlands, see below, pp. 364–8.

1Above, pp. 318–20.

2For Dr. Steven Hales’s treatises on the distillation of sea water, see footnote to the letter cited immediately above.

3In his treatise on “The Animal Oeconomy,” written in 1733 and 1734 and sent to BF in 1745, Cadwallader Colden proposed that the skin “may perspire and absorb at the same time” through “absorbent Vessels intermix’d with the perspiratory Ducts on the external and internal Superficies of the Body.” BF found this theory an improvement on Hales’s hypothesis, advanced in his Vegetable Staticks (1727), that the body was alternately in “imbibing” and “perspirable” states and made “a little Machine to try an Experiment” to test it. See above, III, 33–5, 47. Thus BF’s opinion on the actions of the pores was by no means as “singular” as he implied.

4By 1773 BF had concluded that neither dampness nor wetness caused colds, that their causes were “totally independent of wet and even of cold.” BF to Barbeu Dubourg, March 10, 1773, Dubourg, ed., Oeuvres de M. Franklin (2 vols., Paris, 1773), II, 311.

5In her letter of July 30, 1761, Polly had commented that Hawkesworth was a “dangerous Man” because of his persuasiveness. Writing to BF, Nov. 8, 1769, Hawkesworth reported: “I have just received a Line from the Virgin Mary, and I dine with her at Kensington on Fryday; I hope there will be no Jealousy in Heaven for my wife will be of the Party.” Haverford Coll. Lib.

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