STANDARDS OF LINEAR MEASURE. 
371 
The above Table shows that employing the middle portion of the scale, the 
error in either position is nearly the mean of the errors in the two pre- 
ceding Tables. 
Mr. Dollond’s Scale. 
This scale is upon plate brass, 42 inches long, 1.6 inch wide, and 0.17 inch 
thick ; it contains 41 inches. The scale when placed upon the marble slab 
appeared to be in contact with it throughout its whole extent. 
The wires for elevating the ends were placed under 0 and 41 inches, and the 
wire when the middle was raised was under 20^ inches. 
With wires .05 of an inch diameter. 
From 0 to 36 inches. 
Without Wires. 
A Wire under 
Wires under 
Error when curved 
Error when curved 
Sum of 
the middle. 
the ends. 
upwards. 
downwards. 
Errors. 
div. 
div. 
div. 
div. 
div. 
div. 
32.5 
30.0 
52.0 
32.0 
30.0 
52.5 
32.0 
30.0 
56.0 
31.8 
31.2 
57.0 
30.0 
28.0 
52.6 
30.3 
28.0 
52.6 
Mean 31.4 
29.5 
53.8 
4.4 
19-9 
24.3 
2.5 Reduction to the Chord. 
33.9 
Captain Kater’s Scale. 
This scale is of cast brass, 45.2 inches long, f wide, and 0.29 inch thick. The 
wires, when the ends were elevated, ivere placed under the extremities. 
With wires 0.5 of an inch diameter. 
From 0 to 36 inches. 
Without Wires. 
A Wire under 
Wires under 
Error when curved 
Error when curved 
Sum of 
the middle. 
the ends. 
upwards. 
downwards. 
Errors. 
div. 
div. 
div. 
div. 
div. 
div. 
105.0 
97-0 
137-0 
89.0 
82.5 
128.0 
92.5 
80.5 
123.0 
91-0 
79-0 
128.0 
95.0 
80.0 
128.5 
94.0 
80.0 
131.0 
Mean 94.4 
83.2 
129.3 
13.2 
32.9 
46.1 
2.0 Reduction to the Chord. 
96.4 
