Meafuremeni of a Bafe on Hounflow- Heath. 405 



of. the true length, the fpace in that pofition, comprehended 

 between the two lines on the inlaid ivory pieces, muft be 

 exadly three inches. For the pnrpofe of this adjuftment, the 

 extent o.f three inches was therefore taken from the brais fcale 

 and cut upon the fide of a detached piece of ivory ; which 

 being readily applied to the aforefaid intermediite fpace, the 

 fame was. gradually reduced, by grinding the lips equally, till 

 it exactly correfponded with that taken from the fcale. 



The three rods are numbered, by a cypher on the furface of 

 the metal at each end,. 1.2 ; 3.4; 5.6 ; and that being the order . 

 in which they were to be applied in aclual meafurement, fo it . 

 was likewife the order in which they w^ere adjufted ; that is to 

 fay, the. rod r.z was adjufted with ^^.4, and with 5.6; and 

 the rod 3.4 was, in like manner, adjufted witli 1.2 and 5.6. 



One of thefe deal rods, when finiflied, was found to weigh 

 twenty-four pounds. They were intended to be contained in 

 two chefts, one large and the other fmaller.. The large cheft, 

 which is about 2i feet deep, may be called a double one, becaufe 

 it has two lids that lift quite off, which, in turning upfide 

 down, become alternately top and bottom, having between 

 them, but much: nearer to the one than the other,, a bottom 

 that is common to both. The fhallow fide holds the ftandard 

 rod; and the other, two of the meafuring rods; which lail: is 

 rendered pra6licable by^ having one of the fide braces of each 

 fixed only with fcrews, fo as to be removed and replaced at 

 pleafure. Thus one of the rods rbeing laid in its place, the 

 other is put over it in an inverted pofition; and both having the 

 proper faftenings to keep them in their pofitions, the lid is"'- 

 then put on, and fixed by fcrews. The chelt being now turned 

 upfide down, and the other lid removed, the ftandard i.> 



thereby 



