43^ Major-General Roy's Accowit of the 



the twenty- feventh ftation, or firil: of the third fedlon of the 

 bafe, where the tripod was placed as ulual ; and there it re- 

 iTiained untouched, on account of bad weather, till Monday- 

 the 2d of Auguft. ' 



Confidering how much time and labour had been beftowed in 

 obtaining what we certainly had twQvy reafon to conclude were 

 the befl deal rods that ever were made, it was no fmall difap- 

 pointment now to find, that they were fo liable to lengthen 

 and fhorten by the humid and dry ftates 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 flate, and then to have them carefully painted or 

 varniflied, before they fliould be farther ufed. 



The unfavourablenefs of the feafon, and delays in obtaining 

 the inflruments, had already been the caufes of protrafting the 

 operations on Hounflow-Heath greatly beyond what was at 

 firft expe£led ; and the failure of the deal rods gave no imme- 

 diate profped: of their being fpeedily brought to a conclufion. 

 On revolving in my own mind the different alternatives w& 

 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 fteel. The cumberfomenefs 

 of its weight appeared indeed obje(9:'ionable ; but that incon- 

 venience was either to be fubmitt-ed to, or one of another kind, 

 namely, the reduction of the length, which was always, if 

 poffible, to be avoided. 



S At 



