E 44 1 
bigger, it cannot for the mod part be made life of in 
Steeples and other Places, of confiderable Height, 
where 'tis requifite to obferve * but alfo if it be lefs 
than two Feet, it will not give the Value of the Angles 
with fufficient Exa&nefs. 
As to the other Inftrument for obferving the Arches 
of the Heavens, its Radius ought not to be lefs than 
from twelve to fifteen Feet : but 'tis not neceffary that 
it fhould contain a large Portion of a Circle. Tis 
only requifite to have this Portion fomewhat larger 
than the Arch of the Heavens intended to be mea- 
jfured. Thus, as the Meridians, which may be traced 
in RuJJia , can be extended but between 22 and 23 
Degrees, as already mention'd, it will fuffice, that the 
Inftrument employ'd therein be a Portion of a Circle 
of 30 Degrees. 
M. Ricart, for his firft Operation, got an Arch of 
a Circle made of 18 Degrees and of 10 Feet Radius, 
with which he thought himfelf fure within two or 
three Seconds : And no other Inftrument was made 
ufe of in the chief Obfervations for the Meridian of 
Raris . The Aftronomers who are gone to America , 
carried with them an Inftrument of twelve Feet Ra- 
dius, and of a Portion of a Circle of 30 Degrees. 
But thofe come to Sweden , contented themfelves with 
a Portion of a Circle of five | Degrees, and nine Feet 
Radius: But this Inftrument, made by Mr. George 
Graham , a very able Englifh Mechanician, is by its 
Gonftruftion fo exaft, that the Aftronomers who have 
ufed it, think themfelves fure to two Seconds. The 
one we want for the Obfervations in RuJJia ought to 
be made by the fame Artift, and of the fame Con- 
fou&iom 
