That of 38 degrees as being the middle
latitude of the United States, might seem the most convenient, were
we to consider ourselves alone; but connected with other nations by
commerce and science, it is better to fix on that parallel which bids
fairest to be adopted by them also. The 45th, as being the middle
term between the equator and pole, has been heretofore proposed in
Europe, and the proposition has been lately renewed there under
circumstances which may very possibly give it some effect. This
parallel is distinguished with us also as forming our principal
northern boundary. Let the completion of the 45th degree, then, give
the standard for our union, with the hope that it may become a line
of union with the rest of the world.
The difference between the second rod for 45 degrees of
latitude, and that for 31 degrees, our other extreme, is to be
examined.
The second _pendulum_ for 45 degrees of latitude, according to
Sir Isaac Newton's computation, must be of (2) 39.14912 inches
English measure; and a _rod_, to vibrate in the same time, must be of
the same length between the centres of suspension and oscillation;
and, consequently, its whole length 58.7 (or, more exactly, 58.72368)
inches. This is longer than the rod which shall vibrate seconds in
the 31 degrees of latitude, by about 1/679 part of its whole length;
a difference so minute, that it might be neglected, as insensible,
for the common purposes of life, but, in cases requiring perfect
exactness, the second rod, found by trial of its vibrations in any
part of the United States, may be corrected by computation for the
(3) latitude of the place, and so brought exactly to the standard of
45 degrees.
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