s 
to ascertain a Standard of Weight and Measure. 181 
the mean probable error = ,00016; and that it is 4 to 1 the 
error doth not exceed ■— inch. 
This accuracy is about three times as great as that of Mr. 
Bird's scales, and about equal to that of the divisions of my 
equatorial instrument, made by Mr. Ramsden, in 1791. See 
Phil. T rans. for 1793. 
(§. 52.) I now proceed to the examination of the standard 
rod of Henry VII. which is an octangular brass bar, of about ~ 
an inch in diameter, with one of the sides rudely divided, into 
halves, thirds, quarters, eighths, and sixteenths ; and the first 
foot into inches. Each end is sealed with a crowned old Eng- 
lish H, (If) , and from hence is concluded to be of the 
time of King Henry VII. viz. about 1490, but is now become 
wholly obsolete, since the introduction of the standard of Queen 
Elizabeth ; but such as it is, I have thought proper to examine 
it, and find as follows : 
Inches. 
On this rod, or the 1st foot, is 
equal to 11,973 ouTroughton's. 
the 2d foot is 
the 3d foot is 
11,948 
12,047 
Error, or difference 
The mean foot is 
1 b 9 8 9 
Dmerence. 
— ,011 
on 3 teet. 
~ >°33 
4- yard, or 1 8 inches 
= 1 7>94 6 
— >°54 
— ,108 
~ yard, or 24 inches 
= 2 3 > 9 2 1 
— ,079 
— ,118 
J yard, or 27 inches - 
- = 26,937 
— ,063 
00 
0 
rs 
1 
■J- yard, or 3 1\ inches 
= 3R443 
-.05 7 
~ >°65 
y|- yard, or 33J inches 
= 33 ’ 66 S 
00 
0 
1 
— ,091 
Entire yard, or 36 inches 
- = 35>9 66 
— ,034 
~ ,°34 
And the mean yard - 
= 35,924) 
Mean 
1 
s# 
0 
-vT 
O 
And, by so much, Mr. Troughton's measure is longest. 
