C 5 ] 
Adronomer, to fet out at firft with the Examination 
of the Correftnefs of his Indruments ; and to be af- 
fured that they are Sufficiently exaft for the Ufe he 
intends to make of them : or at lead he fhould know, 
within what Limits their Errors are confined. 
This Prafticc has, in an eminent manner, been 
lately recommended by your Lordfhip’s noble Exam- 
ple ; who having, out of a lingular Regard for the 
Science of Adronomy, erefted an Obfervatory, and 
furnifhed it with as complete an Apparatus of Indru- 
ments, as our bed Artids could contrive ; would not 
fully rely on their Exaftnefs, till their Diviftons had un- 
dergone the drifted Re-examination: whereby they 
are probably now render’d as perfeft in their kind, as 
any extant, or as human Skill can at prefent produce. 
The Lovers of this Science in general, cannot but 
acknowledge their Obligations to your Lordfhip on 
this Account ; but I find myfelf more particularly 
bound to do it; lince, by means of your Lordfhip’s 
mod accurate Observations, I have been enabled to 
fettle fome principal Elements ; which I could not 
at prefent otherwife have done, for want of an In- 
drument at the Royal Obfervatory, proper for that 
Purpofe : For the large mural Quadrant , which is 
there fixed to obferve Objefts lying Southward of 
the Zenith, however perfect an Indrumcnt it may 
be in it felf, is not alone fufficient to determine, 
with proper Exaftnefs, cither the Latitude of the 
Obfervatory, or the Quantity of Refraftion corre- 
fponding to different Altitudes : For it being too 
heavy to be conveniently removed ; and the Room 
wherein it is placed, being too fmall to admit of its 
being 
