•'435 ’Major-General Roy’s Account of the 
the twenty- feventh ftation, or firft of the third feCtion of the 
bale, where the tripod was placed as uiual ; and there it re- 
mained untouched, on account of bad weather, till Monday 
the id of Augufh 
Confidering how much time and labour had been beftoWedin 
obtaining what we certainly had every reafon to conclude were 
the heft deal rods that ever were made, it was no fmall difap- 
pointment now to find, that they were fo liable to lengthen 
and Shorten by the humid and dry Bates of the atmofphere, as 
to leave us no hopes of being able, by their means, to deter- 
mine the length of the bafe to that degree of precifion we had 
all along aimed at. But fince more than one-half of it was 
already meafured, it was judged proper to proceed with them in 
their prefent Bate, and then to have them carefully painted or 
varnifhed, before they fhould be farther ufed. 
The unfavourablenefs of the feafon, and delays in obtaining 
the inBruments, had already been the caufes of protracting the 
operations on Hounflow- Heath greatly beyond what was at 
firft expedted ; and the failure of the deal rods gave no imme- 
diate profpeCt of their being fpeedily brought to a conclufion* 
On revolving in my own mind the different alternatives we 
might ultimately be obliged to have recourfe to, metal rods of 
fome kind or other, whofe expanfion could always be deter- 
mined by experiment, feemed to promife a refult that might 
be fafely relied on. Caft iron was what I had thoughts of 
propofing, knowing from an experiment which I had made 
myfelf, that it expanded lefs than Beel. The cumberfomenefs 
of its weight appeared indeed objectionable ; but that incon- 
venience was either to be fubmitted to, or one of another kind, 
namely, the reduction of the length, which was always, if 
pofiible, to be avoided, 
5 
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At 
