THE NEW NATIONAL STANDAED OE LENOTH, AND ITS PEINCIPAL COPIES. 637 
div. 
Bar lying flat 
+ 37-8 
Pins at 13|^ inches and 46^ inches... 
+ 28-0 
Rollers at inches and 45|- inches 
+ 32*0 
1843. - 
Pins at 15^ inches and 44|- inches... 
+ 32-3 
Sept. 17- 
Pins at 16|- inches and 43|^ inches... 
+ 36-0 
Pins at 174 inches and 424 inches... 
+ 35'5 
Pins at 184 inches and 414 inches... 
+ 38-5 
Bar lying flat 
+ 38-0 
The bar of gun-metal No. 3 was then reduced to the length 37 inches, and lines were 
cut (e\ddently on its upper surface) at the distance 36 inches, and five experiments were 
made on 1843, Sept. 28 and 29. The following is the mean of results: — 
div 
Bar lying flat 
+ 2-41 
Wires under the centre 
+ 5-85 
Wires 2 inches from the centre ... 
+ 9-51 
Wires 4 inches from the centre ... 
+ 9-19 
Wires 6 inches from the centre ... 
+ 7*39 
Wires 8 indies from the centre ... 
+ 4-49 
Wires 10 inches from the centre ... 
+ 1-19 
Wires 12 indies from the centre ... 
— 0-75 
Wires 14 inches from the centre ... 
- 4-11 
Wires I 6 inches from the centre ... 
- 8-69 
Wires 18 inches from the centre ... 
— 11-61 
The same bar was then supported on rollers at different intervals, and eight experi- 
ments were made on 1843, October 10 and 11 ; of which the following are the means : — 
div. 
Rollers 0*75 inch on each side of centre 
0-00 
Rollers 4 inches on each side of centre 
+ 0-06 
Rollers 6 inches on each side of centre 
— 271 
Rollers 8 inches on each side of centre 
- 4-99 
Rollers 10 inches on each side of centre 
— 7-45 
Rollers 12 inches on each side of centre 
- 9-81 
Rollers 14 inches on each side of centre 
-12-93 
Rollers I 6 inches on each side of centre 
— 16-03 
Rollers 18 inches on each side of centre 
— 21-34 
On 1843, October 16, I supplied Mr. Baily with the formulse defining the intervals at 
which rollers ought to be placed beneath a bar in order that the flexure of the bar might 
not influence the measure of the distance between two lines upon the upper surface (the 
rollers being supposed to exert equal pressm’es upwards). With two rollers, the interval 
ought to be 
length of bar 
v/3 
; with four rollers, each interval = with eight rollers, 
V • , 1 length of bar ^ 
each interval = — *. 
^/l5 
Lever-frames were afterwards prepared, each with eight 
rollers. 
It has been remarked above, that Captain Kater had constructed for the Royal 
Society a standard on the principle proposed by himself, of carrying a slender scale in 
a groove cut in a stout bar ; as it appeared probable that the effect of a given degree of 
* See Mem. Astron. Soc. vol. xv. 
4 0 
MDCCCLVII. 
