378 
PROFESSOR 0. REYNOLDS AND MR. W. H. MOORBY 
Whitworth standard 
Laboratory standard 
Laboratory standard 
9-inch gauge. 
gauge, No. 1. 
gauge, No. 2. 
Readings on di- j 
0-0011 
0-00105 
0-00095 
vided wheel of > 
0-00112 
0-0010 
0-0009 
machine J 
0-00114 
0-00097 
0-00098 
Mean readings . 
0-00112 
0-001007 
0-000943 
True lengths . 
9 inches 
9 inches — 0-000113 
9 inches — 0-000177 
These three 9-inch standards, together with the 3-inch Whitworth, therefore gave 
a length wdien placed end to end of 
30 inches — 0‘00029 inch. 
The next operation was to construct a single steel standard with a length of 
approximately 30 inches. This bar being made, and the measuring machine not 
beino’ long enough to accommodate 30 inches, tlie measurements were made between 
the centres of a large lathe in the laboratory. Two centres were made with polished 
flat ends. The one w’as put in the fixed headstock, while the second was carried by 
the movable sleeve of the loose headstock which had previously been securely bolted 
to the lathe bed in a convenient position. A temporary wooden trough was made to 
carry our four short standards, and correctly line them between the two centres. The 
reciprocating centre in the loose headstock was then graduall}^ screwed up till the 
gravity piece of the measuring machine just floated between the end of the adjacent 
standard and the centre. A mark on the hand-wheel actuating the centre was then 
fixed by means of a pointer. The four standards were then removed, and the 30-inch 
bar substituted for them, and the operation of bringing up the centre repeated. The 
circumferential distance then separating the pointer from the mark on the hand-wheel 
was then carefully measured. 
A series of five of these observations were made, and the following readings 
taken, viz :— 
(1) — OT inch (3) -j- 0'09 inch (5) + 0‘03 inch 
(2) — 0'05 inch (4) fl- 0'02 inch. 
Mean = — 0‘002 inch. 
The hand-wheel had a diameter of 9^ inches, and was fixed to a screw of T-inch 
pitch. 
The 30-inch bar was therefore short of the length of the four steel standards by 
0-0000138 inch. 
