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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.
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.”
* * * * * * * * * *