When Franklin arrived in London, he rented rooms on Craven Street, off the Strand, from a landlady named Margaret Stevenson, who also became his domestic (though probably not romantic) companion. More complex was his relation with her daughter Mary, known as Polly. She was a lively and endearing 18-year-old with the sort of inquisitive intellect that Franklin loved in women. In some respects, Polly served as the London counterpart to his daughter Sally. He treated her in an avuncular, and sometimes even paternal, manner, instructing her on life and morals as well as science and education. But she was also an English version of Caty Ray, a pretty young woman of playful demeanor and lively mind. His letters to her were flirtatious at times, and he flattered her with the focused attention that he lavished on women he liked.
Franklin spent hours talking to Polly and then, when she went to live with an aunt in the country, carried on an astonishing correspondence. During his years in London, he wrote to her far more often than he wrote to his real family. Some of the letters were flirtatious. “Not a day passes in which I do not think of you,” he wrote less than a year after their first meeting. She sent him little gifts. “I have received the garters you have so kindly knit for me,” he said in one letter. “Be assured that I shall think as often of you in the wearing as you did of me in the making.”
As with Caty Ray, his relationship with Polly was an engagement of the mind as much as the heart. He wrote to her at great length and in sophisticated detail about how barometers work, colors absorb heat, electricity is conducted, waterspouts are formed, and the moon affects tidal flows. Eight of these letters were later included in a revised edition of his electricity papers. When he came up with the idea of a phonetic spelling system, he used it first in a letter to Polly.
His one concern was that Polly would take her studies too seriously. Even though he appreciated her mind, Franklin flinched when she hinted at her desire to devote herself to learning at the expense of getting married and raising a family. So he provided her with some paternal prodding. In response to her suggestion that she might “live single” the rest of her life, he lectured her about the “duty” of a woman to raise a family.
TO POLLY STEVENSON, JUNE 11, 1760
Dear Polly,
’Tis a very sensible question you ask, how the air can affect the barometer, when its opening appears covered with wood? If indeed it was so closely covered as to admit of no communication of the outward air to the surface of the mercury, the change of weight in the air could not possibly affect it. But the least crevice is sufficient for the purpose; a pinhole will do the business. And if you could look behind the frame to which your barometer is fixed, you would certainly find some small opening.
There are indeed some barometers in which the body of mercury at the lower end is contained in a close leather bag, and so the air cannot come into immediate contact with the mercury: yet the same effect is produced. For the leather being flexible, when the bag is pressed by any additional weight of air, it contracts, and the mercury is forced up into the tube; when the air becomes lighter, and its pressure less, the weight of the mercury prevails, and it descends again into the bag.
Your observation on what you have lately read concerning insects, is very just and solid. Superficial minds are apt to despise those who make that part of creation their study, as mere triflers; but certainly the world has been much obliged to them. Under the care and management of man, the labors of the little silkworm afford employment and subsistence to thousands of families, and become an immense article of commerce. The bee, too, yields us its delicious honey, and its wax useful to a multitude of purposes. Another insect, it is said, produces the cochineal, from whence we have our rich scarlet dye. The usefulness of the cantharides, or Spanish flies, in medicine, is known to all, and thousands owe their lives to that knowledge. By human industry and observation, other properties of other insects may possibly be hereafter discovered, and of equal utility. A thorough acquaintance with the nature of these little creatures, may also enable mankind to prevent the increase of such as are noxious or secure us against the mischiefs they occasion. These things doubtless your books make mention of: I can only add a particular late instance which I had from a Swedish gentleman of good credit. In the green timber intended for ship-building at the king’s yards in that country, a kind of worms were found, which every year became more numerous and more pernicious, so that the ships were greatly damaged before they came into use. The king sent Linnaeus, the great naturalist, from Stockholm, to enquire into the affair, and see if the mischief was capable of any remedy. He found on examination, that the worm was produced from a small egg deposited in the little roughnesses on the surface of the wood, by a particular kind of fly or beetle; from whence the worm, as soon as it was hatched, began to eat into the substance of the wood, and after some time came out again a fly of the parent kind, and so the species increased. The season in which this fly laid its eggs, Linnaeus knew to be about a fortnight (I think) in the month of May, and at no other time of the year. He therefore advised, that some days before that season, all the green timber should be thrown into the water, and kept under water till the season was over. Which being done by the king’s order, the flies missing their usual nests, could not increase; and the species was either destroyed or went elsewhere; and the wood was effectually preserved, for after the first year, it became too dry and hard for their purpose.
There is, however, a prudent moderation to be used in studies of this kind. The knowledge of nature may be ornamental, and it may be useful, but if to attain an eminence in that, we neglect the knowledge and practice of essential duties, we deserve reprehension. For there is no rank in natural knowledge of equal dignity and importance with that of being a good parent, a good child, a good husband, or wife, a good neighbor or friend, a good subject or citizen, that is, in short, a good Christian. Nicholas gimcrack, therefore, who neglected the care of his family, to pursue butterflies, was a just object of ridicule, and we must give him up as fair game to the satirist.
Adieu, my dear friend, and believe me ever, Yours affectionately,
B. Franklin
P.S. Your good Mother is well, and gives her Love and Blessing to you.
TO POLLY STEVENSON, SEPTEMBER 13, 1760
My dear Friend,
I have your agreeable letter from Bristol, which I take this first leisure hour to answer, having for some time been much engaged in business.
Your first question, what is the reason the water at this place, though cold at the spring, becomes warm by pumping? It will be most prudent in me to forbear attempting to answer, till, by a more circumstantial account, you assure me of the fact. I own I should expect that operation to warm, not so much the water pumped as the person pumping. The rubbing of dry solids together, has been long observed to produce heat; but the like effect has never yet, that I have heard, been produced by the mere agitation of fluids, or friction of fluids with solids. Water in a bottle shook for hours by a mill hopper, it is said, discovered no sensible addition of heat. The production of animal heat by exercise, is therefore to be accounted for in another manner, which I may hereafter endeavor to make you acquainted with.
This prudence of not attempting to give reasons before one is sure of facts, I learnt from one of your sex, who, as Selden tells us, being in company with some gentlemen that were viewing and considering something which they called a Chinese shoe, and disputing earnestly about the manner of wearing it, and how it could possibly be put on; put in her word, and said modestly, Gentlemen, are you sure it is a shoe? Should not that be settled first?
But I shall now endeavor to explain what I said to you about the tide in rivers, and to that end shall make a figure, which though not very like a river, may serve to convey my meaning…
[Editor’s note: Here Franklin proceeds to describe in great detail the effects of tides on rivers.]
I have made this letter longer than I intended, and therefore reserve for another what I have farther to say on the subject of tides and rivers. I shall now only add, that I have not been exact in the numbers, because I would avoid perplexing you with minute calculations, my design at present being chiefly to give you distinct and clear ideas of the first principles.
After writing 6 folio pages of philosophy to a young girl, is it necessary to finish such a letter with a compliment? Is not such a letter of itself a compliment? Does it not say, she has a mind thirsty after knowledge, and capable of receiving it; and that the most agreeable things one can write to her are those that tend to the improvement of her understanding? It does indeed say all this, but then it is still no compliment; it is no more than plain honest truth, which is not the character of a compliment. So if I would finish my letter in the mode, I should yet add something that means nothing, and is merely civil and polite. But being naturally awkward at every circumstance of ceremony, I shall not attempt it. I had rather conclude abruptly with what pleases me more than any compliment can please you, that I am allowed to subscribe my self