636 
ME. AIET’S ACCOUNT OE THE CONSTEUCTION OE 
as stated by Mr. Simms, who superintended the construction, and by Messrs. Maudslats, 
who performed the actual casting. The construction of bars with well-holes for the 
defining marks has also been adopted in all the subsequent instances ; but the bars have 
been reduced to the length of 37 inches by Mr. Bailt, and 38 inches by Mr. Sheep- 
shanks. 
After the first experiments applying to the fitness of metals, Mr. Bailt proceeded 
with experiments in verification of some made by Captam EL^tee on the influence of 
small inequalities of the surface supporting a bar. The experiments were made at his 
own house. No. 37, Tavistock Place. The bar of metal No. 3 was notched to half its 
depth at each end, and at each end there was cut a line for microscopic observation on 
the upper surface (the inteiwal of the two lines being 38 inches), and a line for micro- 
scopic observation on the surface at mid-depth (the interval of the two being 39 inches). 
The bar was laid upon a very even bar (whose section is T) in the compaiing-apparatus 
of the Royal Astronomical Society, and the microscopes were adjusted sometimes to one 
pair of lines, sometimes to the other. At the commencement of this and of other series 
of experiments, it is noted that the microscopes were made parallel. The value of one 
division of the micrometer =0-00005 inch. A wire, or pah- of wires, described as “No. 2 
brass wire in my Cavendish experiment,” was placed in difierent positions under the 
bar. [Only one brass wire is mentioned in the ‘ Account of the Cavendish Experiment.’ 
page 29 ; its thickness was 0-0134 inch.] Sometimes the bar was placed on rollers. The 
folloAving are variations in the measure of the intervals of the lines, under difierent cu-- 
cumstances. Each number is the mean of several experiments. 
1843. 
Sept. 14. 
r 
Lines on upper surface ■<{ 
L 
Bar Iving flat 
Wires under the ends 
Wires under the middle 
div. 
0-00 
-14-35 
-t- 6-05 i 
Lines on surface at mid-depth... < 
Bar lying flat 
Wires under the ends 
Wires under the middle 
0-00 
+ 2*50 ' 
— 2-50 : 
Sept. 15. 
Hollers 8 inches from centre ... 
Rollers 10 inches from centre ... 
Rollers 12 inches from centre ... 
-f 24-68 
-f21-92 
+ 17-94 
L 
Rollers 6 inches from centre ... 
Rollers 10 inches from centre ... 
Rollers 14 inches from centre ... 
+ 25-12 
+ 19-76 
+ 12-80 
Sept. 16, 
Lines on upper surface <; 
Bar lying flat 
Wires 8 inches from centre 
Wires 10 inches from centre 
Wires 12 inciies from centre 
Wires 14 inches from centre 
Wires 16 inches from centre 
0-00 
+ 6-65 
+ 5*30 
+ 3-17 : 
- 0-17 
— 5*45 
The following experiment is on the middle 3 feet of Mr. Bailt’s tubular 5-foot scale. 
No. 5. The lines on the upper surface. [It would seem that it took a faulty bearing 
Avhen laid flat on the bar.] Single readings. 
