434- ’ Major-General Roy’s’ Account of the 
TLxpanfion of the Deal Rods . i 
It has been an opinion generally enough, although, as we. 
have feen, erroneoufly received, that very ftraight- fibred deal 
was not at all, or but little, affedted longitudinally by the hu- 
midity of the air. That we might not be led affray by truff- 
ing to fallacies of this fort, the ftandard rod had been provided ; 
which being always clofely (hut up in its cheff, except during 
the fhort interim of comparifon, could feel but a fmall propor- 
tion of the effedts which the meafuring rods buffered, thefe 
being conftantly expofed to the open air throughout the day, as 
well as to the moifture of the night* when lying under the 
oil-cloth canopy. The ffandard rod, it is true, could not be 
accurately compared with the brafs fcale : for although when 
conffrudted, brafs pins, forty inches afunder, had been driven 
into its ftera, for the purpofe of fuch comparifon, yet thefe 
had afterwards been difplaced, or at leaf the points upon them 
defaced, by the planing over of the upper furface. This cir- 
eumftance, which was unattended to when the operations 
commenced, is now of no confequence ; becaufe, from an ex- 
periment hereafter to be mentioned, the lengthening of the ffan- 
dard may be pretty nearly afcertained. But ff nee there are fome 
contradidtory circumftances, boon to be mentioned, in the ope- 
ration with the deal rods, which would have made a repetition 
of it .abfolutely neceffary, if we had not now obtained thofe of 
a different kind, fo very unexceptionable in their nature and 
mode of application, as, in the prefent cafe, to admit of no 
competition between the two rebuffs, and to render it improper 
on our part ever to have farther recourfe to the firff s fo there 
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