G54 
ME. AIET’S ACCOUjS’T OF THE COXSTEECTIOX OF 
doAvn the standard on different metals and substances ; and yet the comparison of them 
might be very important hereafter, for twenty years seem to do or tell a great deal in 
relation to Standard measures.” 
After deliberation it was 
Resolved, — That at present the Committee see no reason for departing from their 
resolution of the 11th of July, 1843 — “ That the material employed for the construction 
of the Parliamentary Standard of Length be beU-metal or steel, as ]SL-. Bailt may think 
best,” — as explained by Mr. Bailt at the meeting of the 10th of November, 1843, when 
Mr. Bailt recommended an alloy of copper and tin. 
I may here appropriately give some description of the apparatus which Mr. Sheep- 
shanks employed. 
First, for the thermometers. The apparatus for the freezing-point (the usual small 
vessel for containing pounded ice or snow, admitting of drainage of supei’fluous water), 
and the apparatus for the boiling-point (a small covered saucepan, with a mercurial 
gauge, and a hole for the thermometer-stalk), require no further description. In the 
operations for breakmg the column of quicksilver, Mr. Sheepshanks never tnisted to 
subdividing the graduations of the thermometer-tube by eye. The tube was laid in a 
horizontal position ; and a microscope pointing downAvards, mounted in a frame which 
admitted of horizontal motion above the tube, was directed successBely to each end of 
the column of quicksilver ; and at each end three readings of the microscope-micrometer 
were taken, namely, one for the end of the quicksilver-column, and one for each of the 
graduations preceding and following that end of the quicksilver. A numerical computa- 
tion was then required for determining the factional part of the tube-graduation corre- 
sponding to the position of the end of the quicksilver-column. This operation, though 
very exact, occupied much time ; it might "without doubt have been facilitated by proper 
mechanical an’angements, of which howeA^er Mr. Sheepshanks never availed himself. 
Secondly, for the comparison of 3-foot bars. The apparatus estabhshed in the cellar- 
of the Royal Astronomical Society’s Apartmeiits in Somerset House aauU be understood 
from the diagrams in Plates XXVIII., XXIX. and XXX., to which the folloAving expla- 
nations apply. 
Figure 1, Plate XXVIII., is a ground-plan of the apparatus. The trough for enclosing 
the case which actually contained the bars is entirely omitted. The observer’s station (or 
what may be considered the front of the apparatus) is the loAver part of the diagram. 
A, A, &c. is a wooden enclosure, covering the back and (partially) the sides, and 
extending from the floor nearly to the ceiling of the room. 
B, B, &c. is the general platform of masonry. 
C, C are the two stone piers. 
D, D, a horizontal slab extending right and left ; resting on the top of the piers. 
EiE, EE, two solid transoms of stone, resting upon DD; they cai-ry the two microscopes. 
FF, a slab resting upon the two transoms. 
