646 
ME. AIET’S ACCOrXT OE THE COXSTEUCTIOX OE 
worthy, but the injurious effects of then’ supports, and an uncertainty in the temperature 
referred to one thermometer, introduced great irregularities in their comparisons and 
doubts in the reductions of them. The Royal Society’s Scale had been carefully con- 
structed in reference to one apprehended cause of eiTor ; but it seemed likely that a 
construction so complicated might introduce other eiTors of equal magnitude ; and it 
appeared certain that the form already partially introduced (a stiff bar supported at 
many points by free roller-motion) would be far less liable to error. Finally, there ran 
through the whole of these comparisons one specific cause of uncertainty ; nobody knew 
the authority for any one of the thermometers used, no one doubted that they might 
be very sensibly in error, and two thermometers inclosed in the same box and intended 
to be used with the two Ordnance Bars actually differed an entme degree. 
It was plain therefore that, either in the scientific or in the legal sense, the restoration 
of the Standard was indeterminate. The formation of a New Standard must be an 
operation de novo ; the length must be confined within certain limits (wide in the scien- 
tific, narrow in the commercial sense), but within these it might have any definite value ; 
and when that definite value was fixed, it must in no way be again referred to the old 
standards or scales, whether original or intermediary. The principal object now was. 
to ensure constancy and definiteness to the new Standard and its copies, and means 
of reducing without sensible error the comparisons which might be made with them. 
As far as depended on the Standard itself, it was hoped that the constmction adopted 
gave sufficient security. As regarded the means of making comparisons, a far ffi-mer 
apparatus than had hitherto been used was requisite. As regarded the effects of tempe- 
rature, it was necessary to create an entirely new system of thermometers, founded upon 
the natural constants, to be determined by appropriate physical experiments ; and to 
use them in new determinations of thermometric expansion. 
Such is the state in which the problem was left to Mr. Baily’s successor. 
Section IV. — Proceedings of the Committee and of Mr. Sheepshanks to 1847, June ; con- 
struction of new Thermometers, and erection of Comparing Ajjparatus ; description 
of the Apparatus, and of Mr. Sheepshanks’ method of comparing. 
The Committee at their meeting of 1844, November 30, received uith pleasure and 
thankfully accepted Mr. Sheepshanks’ offer to continue the work commenced by 
Mr. Baily. Intimation of this arrangement being given to the Lords Commissioners of 
the Treasury, a request to the same effect was addressed by them Lordships to Mr. Sheep- 
shanks and assented to by Mr. Sheepshanks ; Mr. Sheepshanks, like Mr. Baily, dec lining 
to accept pecuniary remuneration. I had received from Mr. Baily’s representativ es the 
four bars on which the restoration of the standard was to be founded, as also the MS. 
books of comparisons, and I placed them in Mr. Sheepshanks’ hands. 
At the Meeting of 1845, June 6, Mr. Sheepshanks communicated a Report to the 
following effect : — 
“ The object proposed appears to be the restoration of the length of the lost Parlia- 
