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.
A machine, says the remarker, to measure the mean motion, will be far preferable to any other method yet proposed; and immediately afterwards he confesses, he cannot conceive that a true meridian can be found at sea, to several minutes. Now this “uncertain error” must certainly affect any other machine for that purpose, as well as Wood’s Sand-Glass, and exceed the error occasioned by turning the glass somewhat quicker at one time than another. Besides, it would not be easy to shew, why a machine to measure the Earth’s mean motion on its axis, with respect to the Sun, will be preferable to one that will measure the Earth’s true motion on its axis, with respect to the fixed Stars.
I would not be thought to recommend Wood’s project. He himself takes notice of two disadvantages attending it, viz. the wearing of the orifice through which the sand passes, and the sand itself becoming polished in time, so as to run more freely; to which if we add, that perhaps it may be greatly affected by heat and cold, there seems to be but little probability of its usefulness. Nor do I see how it can even have the merit of being new: for the scheme itself, with all the remarker’s objections that have any weight in them, must readily occur to every person that thinks at all on the subject. I shall only observe, that it appears doubtful to me, whether the remarker does not equally deserve the censure he so freely bestows on Mr. Woods—“His works are full of errors, and his writings of contradictions.”
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I remain your affectionate brother.
David Rittenhouse.
Dr. Rittenhouse’s Chronometer.
The construction of this Time-piece is thus described by Mr. Henry Voight, chief coiner in the Mint, heretofore an eminent clock and watch maker in Philadelphia; an artist of great ingenuity, and well known for the excellence of his workmanship. The description is given in Mr. Voight’s own words.