402 Major-General Roy’s Account of the 
ham’s property, would correfpond with thofe above-mentioned, 
which he had been dire&ed by the Royal Sociey, with fo much, 
care and pains, to provide; yet, that nothing of this fort 
might remain doubtful, it was judged right, in fettling the 
abfolute length of the bafe, which I meafured near London 
in 1783, as has been mentioned in the introduction to this 
Paper, that the two fcales Ihould be actually compared. Hav- 
ing accordingly obtained an order from the Prefident, for ad- 
million into the Society’s Apartments, I went there in the 
afternoon of the 13th of Auguft, and laid both fcales taken 
out of their cafes on the table of the meeting-room, with 
thermometers along-lide of them, that they might acquire 
the fame temperature. On the' forenoon of the 15th of Au- 
guft: the companion was made, with the afliftance of Mr. 
Ramsden, who for that purpofe carried along with him his 
curious beam-compaifes, whofe micrometer-fcrew ftiews very 
perceptibly a motion of _^ T ^th part of an inch. Thus the 
extent of three feet, being carefully taken from the Society’s 
ftandard, and applied to my fcale, it was found to reach exactly 
to 36 inches, the temperature being 65°. In ]ike manner, the 
^ 
beam-compaftes being applied to the length of the Exchequer 
yard, the extent was now found by the micrometer to over- 
reach that yard by T -^JL^th, or nearly parts of an 
inch. 
Having thus fhewn that my fcale is accurately of the fame 
length with the Society’s ftandard, it remains to point out the 
•ufe that was made of it, for afcertaining the lengths of the 
deal rods, intended for the operation on Hounllow- Heath. In 
the firft place, Mr. Ramsden prepared a beam-compafs, fuf- 
ficient to take in twenty feet, trufled in all refpeds like the 
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