594 PROF. J. J. THOMSON AND MR. O. F. C. SEARLE ON THE RATIO OF THE 
the time of compai’ison we shall simply have to correct the metre to 16° C. The 
temperature of the room never differed from 16° by more than 2°, so that no 
appreciable error can be introduced on tins account. 
External Diameter of Inner Cylinder. 
The sliding calipers of the laboratory were used to measure this. The bar of the 
calipers rested on the flat top of the cylinder, so that the calipers could be moved 
backwards and forwards along the top. The jaws are supposed to be at right angles 
to the bar along which the sliding one moves, but this was found not to be exactly 
the case. To obviate this difficulty a small piece of brass was fastened to the end of 
one jaw, so that the contacts were made at the ends of both jaws. The calipers were 
then placed under the microscope and two definite marks read off. The standard 
metre was then placed beneath the microscopes and treated in the same way. The 
distance between the marks when the jaws of the calipers were in contact was 
determined by the micrometer screw alone. 
The readings of the screws are given in terms of ^ inch. 
Maximum Diameter of top end of Cylinder. 
Calipers. 
23 8 cm. 
Left-hand screw. 
Right-hand scj-ew. 
Left-haiid screw. 
Right-hand screw. 
1 
1-1765 
-6643 
1-2308 
-5970 
2 
l-l;'30 
-6420 
1-1939 
-6280 
.S 
1-8100 
-5642 
1-7980 
-5648 
4 
1-8676 
-5134 
1-8793 
-4965 
The numbers in (4) are the mean of three readings. 
These measurements gave as the distance between the marks— 
23‘8 cm. 
— •00260 in. 
(1) 
. . . --00262 „ 
(‘^) 
7 ? * • 
. . . --00220 „ 
(3) 
9 ) • • 
. . . —-00104 ,, 
(^) 
23-8 cm . . 
. . . —-00211 in. 
= 23-7946 cm. 
Distance between the marks with jaws of calipers closed. Read with left-hand 
screw- 
