Part 103

DAVID RITTENHOUSE, Vice-President.

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Footnote A40:

See page 320 of the foregoing Memoirs.

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Some Remarks of Mr. Rittenhouse, on the famous Problem of Archimedes.

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Footnote A41:

See page 154 of the foregoing Memoirs.

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To the Printers of the Pennsylvania Gazette.

Philadelphia, Oct. 8th. 1767.

Gentlemen,

In your paper, No. 2017, an ingenious gentleman who signs himself T. T. has favoured the public with remarks upon that celebrated saying of the famous Syracusean geometrician: “Give me a place to stand on, and I will move the Earth.” When these remarks appeared, I was engaged in matters that would not allow me to pay that attention to them, which they deserved. The justice, however, due to Archimedes, and the respect I bear for that truly great man’s memory, oblige me now (though late) to offer my sentiments upon this interesting subject.

I readily agree with your sensible correspondent, as to the conclusion he has drawn from the principles whereon he seems to have founded his calculation, without being at the trouble to examine his numbers. All that I propose is, to place this grand mechanical problem in another light, wherein it will appear more feasible.

If a ball of earth, weighing 200 pounds, were left at liberty near the surface of this globe, it would descend, by its own gravity, about 15 feet in one second of time, and about 20 miles in 80 seconds: And if, as this gentleman supposes, there are about 2000 trillions of such balls in the whole Earth,—the Earth, by their mutual attractions, in 80 seconds of time; will move toward the ball 1/1736,000,000,000,000 of an inch; and if the same force were to act continually for 105 years, it would move about one inch. Therefore, the force wherewith a man acts, when he lifts a weight of 200 pounds, if applied without intermission for the space of 105 years, is sufficient, without any machinery, to move the Earth one inch in that time; and it must, from the velocity received by that force alone, continue for ever after to move at the rate of one inch in about 50 years.

A MECHANIC.

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Footnote A42:

Mr. T. T. proceeding on a different supposition, has computed twenty-seven billions of years necessary for that purpose.

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Letter from Mr. Rittenhouse, to the Rev. Mr. Barton.

Norriton, July 20th. 1768.

Dear Brother,

In Hall and Sellers’ paper of last Thursday, we have some curious remarks on an Essay for finding the Longitude, lately published in the Pennsylvania Chronicle, and which I had before seen in the London papers.

The first remark is no doubt just, and is perhaps the only one made, which Mr. Wood’s essay gave just occasion for; how he could commit such a mistake, is not easy to conceive. But the remarker immediately charges him with another: for he tells us, that he (Mr. Wood I suppose) says, that Mr. Harrison’s Machines were finished about Christmas 1765; whereas his father (whether Wood’s father or Harrison’s, is not clear,) made three, which the remarker saw in motion about 18 years since. He then proceeds to assure us, (by the spirit of prophecy I presume, at least I cannot conceive how he could come by this piece of knowledge in a natural way,) that neither the father or his son will ever be able to finish their machines.