648 
ME. AIET’S ACCOTJ^fT OE THE COXSTEHCTIOX OF 
“ The bars when under examination to be placed in a drop-box surrounded by a large 
mass of water. 
“ For ascertaining actual thermometric expansion, the drop-box of one bar is to be 
placed in ice, and that of the expanding bar in water of different temperatures, and 
these are to be compared repeatedly by the microscopes. [This arrangement was not 
precisely carried out.] A similar method will be used for ascertaining whether after 
repeatedly heating and cooling one bar, it returns to the same length. [This was not 
specially done.] 
“ Bars of iron, copper, and cast steel, have been prepared, in addition to the bars of 
gun-metal prepared under Mr. Bailt’s direction. IVIr. Sheepshaxks proposes to com- 
pare carefully bars of these metals and alloys, and also to determine then' minimum 
time of vibration, and after some time to repeat these observations. The object of this 
is to ascertain the permanency of the bars. For the \ibration obseiwations, apparatus 
for swinging in vacuo is now in preparation. [This was not effected.] All these opera- 
tions ought to precede the comparisons for restoration of the lost standard. 
“ Mr. Sheepshajvks then remarked that (for reasons akeady given) it appears impos- 
sible to restore the standard with reasonable accuracy, and he suggested therefore for 
consideration whether it might not be better to adopt the length which has been used in 
the measurement of Colonel Colby’s base for the Trigonometrical Siuvey of Ireland. 
This appears permissible, because there is sufficient latitude in the vagueness of com- 
parison of the old standard to allow it; and it appears worthy of recommendation, 
because (as Mr. Sheepshanks understands from Colonel Colby) the length adopted in 
the Irish base appears to correspond very exactly -with the length adopted in General 
Boy’s base on Hounslow Heath. Logically there is no inconsistency in this coui'se. 
because the divisions of the lO-feet iron bars used by Colonel Colby were laid do^Mi fi-om 
Teoughton’s scale, from which also the divisions of Sir Geoege Shucebuegh’s scale 
(judged by Captain Katee to be equivalent to the old Parliamentary Standard) were laid 
down. Mr. Sheepshanks proposed therefore to make a 3-foot iron bar, to compai-e it 
with the scales which were directly compared with the old Parliamentary Bar (for 
general information), and to multiply it by and then to compare it with Colonel 
Colby’s lO-feet bars ; and from this latter comparison to infer the length proper for tlie 
new National Standard. 
“ A subsequent process, but still distant, would be the preparation for comparisons 
with measures a bouts and for pendulum experiments.” 
The following are further extracts from the Minutes of the same meeting (1845, 
June 6): — 
“ Mr. Aiey stated, in reference to the question of the use of alloys or pure metal, that 
he had just heard that great difficulty had been experienced by Messrs. Maudslays in 
casting a bar of pure copper ; the cast being honey-combed and full of bubbles. 
“ On consideration of Mr. Sheepshanks’ report, it was Besolved, — 
