Mecifurement of a Bafe on Hounflow-Heath. 405 
of the true length, the fpace in that poiition, comprehended 
between the two lines on the inlaid ivory pieces, mu ft be 
exactly three inches. For the purpofe of this adjuftment, the 
extent of. three inches was therefore taken from the brafs fcale 
! and cut upon the fide of a detached piece of ivory ; which 
being readily applied to the aforefaid intermediate fpace, the 
j fame was gradually reduced, . by grinding the lips equally, till . 
I. it exactly correfponded.with that taken from the fcale. 
The three. rods are numbered by a cypher on the furface of 
; the metalat each endy 1 .2 ; 3.4; 5.6; and that being the order 
in which they were to be applied in adlual meafurement, fo it - 
I was likewife the order in which, they were adjufted ; that is to 
; fay, the. rod 1.2 was adjufted with 3.4, and with 5.6; and 
! the rod. 3. 4. was, in like manner, adjufted with 1.2 and 5.6. 
One of thefe. deal rods, when finifhed* was found- to weigh , 
! twenty- four pounds. They were intended to be contained in 
1 two chefts,. one large and the other fmalleiv The large cheft, 
1 which is about 2| feet deep, may be called a double one, becaufe . 
j it has two lids that lift quite off, which, in turning upfide 
down, become alternately top and bottom, having between 
! them, Tut 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 laft is 
rendered practicable by-. having one of the tide braces of each * 
fixed only with fcrews, fo as to be removed and replaced at ; 
pleafure. Thus, one of the rods being laid in its place, the 
other is put over it in an inverted pofition ; ;and both having the 
proper faftenings to keep, . them bn 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 is 
