NEWTONIAN CONSTANT OF GRAVITATION. 28 
The interval 1:00 to 5°00 was compared with the difference between an 11-inch and 
a 7-inch Whitworth standard bar. Assuming the difference to be 4 inches, this 
interval was found to be 3°99970 inches. In the same manner the interval between 
zero (really 0°4) and 6:00 was found by comparison with the difference between a 
12-inch and 6-inch Whitworth standard bar to be 5°95996 inches. 
The distance from 6°00 to each of the divisions up to. 6°05 was measured in the 
Whitworth machine, and also by means of the micrometer screw of the optical 
compass. The value of the screw was found in terms of the middle inch of the scale, 
which had been measured most carefully upon the Whitworth machine. The screw 
measures were found short by ‘145 per cent. Allowing for this the distances were 
found to be :— 

Corresponding totals 
Between | By serew corrected.| Total from 6:00. measured in 
Whitworth machine. 


6-00 and 601 010145 010145 OLOLS 
601 ., 6-02 “010105 020250 02019 
| 6-02 ., 6:03 009815 030065 03002 
6-03 ., 6:04 009915 039980 03995 
| 6-04. 



» 6:05 010095 050075 05012 

Adding the measures of the intervals -04 to 6°00, and 6:00 to 6:04, the sum is 
5°99994 or 5°99991 according to the value taken for the smaller interval. Mr. CHANEY 
allowed me to measure the distance from ‘04 to 6°04, at the Standards Office, by com- 
parison with the intervals 24 to 30 and 30 to 36 in the standard yard measure. The 
two measures did not differ by an amount that could be detected and the result was 
found to be 5°99995 at the temperature 59°7 F. There was no question, therefore, 
that the 6-inch distance was known correctly to one part in 100,000. 
The distances from 2°50 to 2°55 and from 3°45 to 3°50 were measured by the micro- 
meter screw of the optical compass, and their sum was found to be (employing the 
corrected value of the screw) ‘100125, so that the distance between the divisions 2°55 
and 3°45, which are those actually used in all the measures of the horizontal distances 
between the fibres, is 89967. There can be little doubt that this is correct to one part 
in 10,000 and, as a small error in the working length of the beam produces an error of 
about the same magnitude in the result, the value of G is not likely to be affected 
seriously by uncertainty in the value of this inch. I did not attempt to determine 
this inch at the Standards Office, as I found that, owing to the coarseness of the lines 
on the standard bars and the imperfect optical means, so small a distance could not be 
measured with a high degree of proportionate accuracy. Should the rest of the ex- 
periment ever be carried out with such perfection that a possible doubt of one in 10,000 
on this measure becomes of importance (and I see no reason why it should not), then 
I should have to rely upon a measurement made at the International Bureau at 
