Benjamin Franklin Papers

From Benjamin Franklin to Thomas Clap, 8 November 1753

To Thomas Clap

ALS: Yale University Library

Philada. Nov. 8. 1753

Dear Sir,

The first Intimation I find of the New Airpump, is in a Piece of Mr. Watson’s, read to the Royal Society, Feb. 20. 1752 where describing some Experiments he made in Vacuo, he says, “The more compleat the Vacuum, caeteris paribus, the more considerable were the Effects; and here I should not do Justice to real Merit, were I silent in regard to Mr. Smeaton. This Gentleman, with a Genius truly mechanical, which enables him to give to such Philosophical Instruments as he executes, a degree of Perfection scarce to be found elsewhere; this Gentleman, I say, has constructed an Air pump, by which we are impower’d to make Boyle’s Vacuum, much more perfect than heretofore. By a well-conducted Experiment, which admits of no doubt as to its Truth, I have seen by this Pump the Air rarified to 1000 Times its natural State; whereas commonly we seldom arrive at above 150. As the promotion of the mechanic Arts is a considerable Object of our excellent Institution, if this Gentleman could be prevail’d upon to communicate to the Royal Society that particular Construction of his Air pump, which enables it to execute so much more than those commonly in Use, it would not fail to be an acceptable Present.”3 So far Mr. Watson. [In the] April following, was read a Letter from Mr. Smeaton in which he describes his Improvements, and [gives a] Draft of his Pump; the whole too long to transcribe4 but it appears to me that the Machine being rather simplify’d than made more complex, can scarce cost more than one of the old Sort, tho’ the Price is not mention’d. By only turning a Cock it is at pleasure made a Condensing Engine. An Advantage the others have not.

I have seen nothing of your Searchers. Mr. Parker has receiv’d Bower,5 but writes me, that he is at a Loss how to send it, and desires you would order somebody to call for it.

I shall send the Dollars for Mr. Mix6 per next Post: For I fancy you will not now buy this Apparatus here, but chuse the new Airpump from England.7

My Respects to all Friends, concludes, from Dear Sir, Your obliged humble Servant

B Franklin

Mr. Eliot

I tho’t it best to send this to You that so You might better Describe it to Mr. Collingson. I desire You would send it to me again.

T. C.

Addressed: [torn] Clap  [torn] the College at  Newhaven  [torn]

Addressed [by Clap]: the Rev  Mr Jared [Eliot]  of  Killingworth

[Note numbering follows the Franklin Papers source.]

3William Watson, “An Account of the Phaenomena of Electricity in vacuo, with some Observations thereupon,” Phil. Trans. XLVII (1751–52), 363–76. The quoted material is on p. 364.

4John Smeaton, “A Letter to Mr. John Ellicott, F.R.S. concerning some Improvements made by himself in the Air-Pump,” ibid., pp. 415–28.

5On Archibald Bower’s History of the Popes, see above, IV, 213n.

6On Samuel Mix, see below, note 8.

7“Sundry Gentlemen” contributed £18 to buy an air pump for Yale College. Jared Eliot ordered it through Peter Collinson. There was a delay in shipping it, for which Collinson apologized (to Eliot, Dec. 15, 1755, MS, Yale Univ. Lib.), regretting the “Check to the Improvement of Natural Knowledge,” and wrote “a Thundring Letter” to the maker. The instrument arrived in May 1756. It was described in 1786 as “tolerably good,” but Benjamin Silliman thought in 1792 that it “would, with difficulty, kill a mouse, when placed upon its plate under a receiver, so imperfect was its exhaustion.” Henry M. Fuller, “The Philosophical Apparatus of Yale College,” Papers in Honor of Andrew Keogh (New Haven, 1938), pp. 163–80.

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