178 Sir George Shuckburgh Evelyn's Endeavours 
0,3 inch thick ; bearing a scale of 90 inches, or equal parts, 
each subdivided into 10, with a vernier at the commencement, 
being a scale of 100 divisions to 101 tenths. This has been 
called Mr. Bird's own scale, viz. made for his own use; and 
was the instrument with which he is said to have laid off the 
divisions of his 8-feet mural quadrants. It is probable that 
Mr. Bird made many more of these scales, now in the hands 
of private persons, (one of which, indeed, I saw at the Presi- 
dent De Saron's, many years ago, at Paris,) but those have 
not come to my knowledge. 
(§. 48.) In comparing General Roy's (Bird's) scale with 
Mr. Troughton's, I found 42 inches of the former were 
= 42,000 10 inches on Troughton's; (the thermometer 5 1°,7;) 
3 6 inches were consequently = 36,00008. 
And 12 inches on the 1st foot were equal 
to the 12 inches from 12 to 24 on 
Troughton's scale 
The 2d foot - 
The 3d foot - 
The last foot - 
> — ,0003 
-f ,0006 
— ,0004 
-|- ,0006 
Inches. 
: n>9997 
12,0006 
1 1 , 999 6 
12,0006 
The mean foot, therefore, in General Roy's scale, 1 
taken from four different feet, compared with I 
Troughton's, between the 12th and 24th inch, f 12,00012 
is as 12 to - - - - J 
That is, General Roy's scale is longest on 1 foot by 
so much, and longer on 3 feet by - ,00036 
And the greatest probable error from the inequality 
in the divisions is about - - ,0005 
And the mean probable error about - - >0003 
(§. 49.) Mr. Aubert's scale, compared with Mr. Trough- 
ton's, was as follows : 38 inches were equal to 57,9982 inches 
