be fo adapted that their two Edges, which are next to the 
Gmmon, may be perpetually in the fame Plane with their 
correfpondent edge of the Gmmon . On the Scile-Ruler he 
puts TeieJ copied Sights^ with Crolf-hairs in their due place. 
This Inftrament is reprefented by a large Scheme annexed 
to the end of the Book . How every part of this Inftrument 
mull be framed, and the Stile-Nut and Ruler- Joynt com- 
pofed, is at large defcribed in the ^th. Chapter. As for Te- 
lefcopick Sights^ and their true adjufting j he tells Chap. 5. 
how to put in the Menfumtor^ or to place the interfedion 
of the Crofs-Hairs, fb that they may ftand neither too high 
nor too low, nor too much to the right or kft Hand, which 
elfe would produce Errors in the Azimuths and Altitudes : 
alfo for making the Line of Sight ox CoUimation parallel to the 
fides of the Ruler, he applyech two Pins, which willierve in 
tlie fame manner for finding the Declination of the Magnet, 
whereas the Ways propofed by Mr. HmttviliedsASturmiuSj 
fcem to b^ defedive. The way of letting the Dial to his 
true Pofitibn, is explained in the 6/^. Chap, where he tells 
that two things are requifite, firft that the plain of the Dial 
be in an exad Horizontal Pofture, by accurate Levels , and 
fecondly, that the Meridian, or 12 a Clock-Line, be exaftly 
towards South and North ; for that being 12 minutes of a 
Degree ill placed, will make a Dial err a minute of Time, 
in the Latitude of 5 3 Degrees : and for this Reafon he fhew- 
eth Chap. 7. how to find the Meridian Line by his Infl:ru- 
ment, in taking feveral equal Altitudes of the Sun in the fore 
and afternoon, and having drawn the Azimuths thereto, the 
Bifeftion of the included Angles, will fhew the true Meri- 
dian Line, which alio may be found after the fame manner 
at night by the Scars. But coming finally in the %th. Chap, 
to the manner of obferving the Time^, after the Dial is juftly 
levelled and ftated ; he fhews it to be done by looking at the 
Sun through the Teiefcopick or Stile Ruler, and bringing 
the Menfurator upon the Slios C enter; and then the Hori- 
zontal Ruler lhall cut the hour, minute, and part of a mi- 
D d nute 
