Graham; that the Royal Society had had a brass rod made
pursuant to their experiments, which was made so accurately, and by
persons so skilful and exact, that it was thought not easy to obtain
a more exact one; and the committee, in fact, found it to agree with
the standards at the exchequer, as near as it was possible. They
furnish no means, to persons at a distance, of knowing what this
standard is. This, however, is supplied by the evidence of the
second pendulum, which, according to the authority before quoted, is,
at London, 39.1682 English inches, and, consequently, the second rod
there is of 58.7523 of the same inches. When we shall have found,
then, by actual trial, the second rod for 45 degrees by adding the
difference of their computed length, to wit: 287/10000 of an inch, or
rather 3/10 of a line (which in practice will endanger less error
than an attempt at so minute a fraction as the ten thousandth parts
of an inch) we shall have the second rod of London, or a true measure
of 58 3/4 English inches. Or, to shorten the operation, without
varying the result,
Let the standard rod of 45 degrees be divided into 587 1/5
equal parts, and let each of these parts be declared a line.
10 lines an inch, 5 1/2 yards a perch or pole,
12 inches a foot, 40 poles or perches a furlong,
3 feet a yard, 8 furlongs a mile,
3 feet 9 inches an ell, 3 miles a league.
Pages:
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123