i^6 Gen. Roy’s Account of 
or of Heel, are diftinguifhed from each other. And here it is 
neceffary to obferve, that the plates muftvnot only be fre- 
quently confulted, but alfo attentively confidered, and repeat- 
edly compared with each other, in the courfe of this de- 
icription. 
Art. II. General view of the in/lrument . 
It is a brafs circle, three feet in diameter, and may be called 
a great theodolet, rendered extremely perfect ; having this ad- 
vantage in particular, which common theodelets have not, that 
its tranfit telefcope can be nicely adjufted by inverfion on its 
fupports ; that is to fay, it can be turned upfide down, in the 
fame manner that tranfit- inftruments are, in fixed obfervatories. 
The circle is attached by ten conical tubes, as fo many radii) 
to a large vertical, conical hollow axis of twenty- four inches 
in height, which may be called the exterior axis. Within the 
bafe of this hollow axis, a collar of call fteel is ftrongly 
driven ; and on its top there is inferred a thick bell-metal 
plate, with Hoping cheeks, which, by means of five fcrews* 
can be raifed or deprefled a little. 
The inftrument refts on three feet, which are firmly united 
to each other at the place where they branch off, by a ftrong 
circular plate of bell-metal, upon which rifes another vertical 
hollow cone, of lefs fize than the former, being included 
within it, and is therefore called the interior axis. On its top 
is inferred a caft-fteel pivot, with Hoping cheeks, paffing 
through the bell-metal plate on the top of the exterior axis, 
the cheeks of the one being nicely ground to fit the cheeks of 
the other. The bell-metal bafe of this interior axis is in like 
manner ground to fit the caft-fteel collar in the bafe of that 
which is without it. Thus the circle being lifted up by two 
men 
