n6' Sir George Shuckburgh's Account 
as this will seldom happen, from the same reasons as have al- 
ready been mentioned, I prefer taking a memorandum of this 
quantity also, and allowing for it ; by which means I see its 
alteration, from time to time, compared with the weather, 
know better what I am about, than if I attempted to correct 
it, and save a great loss of time. From hence it must be 
seen that nothing is depended on, but that the instrument 
keeps its place during the four or five minutes that the ob- 
server is occupied in making the observation. 
(31.) The instrument is now prepared for an observation 
over the meridian, and also of the polar distance ; at which 
moment, if the weather should be cloudy, the observation in- 
complete, or unsatisfactory, it may be repeated as many 
times afterwards as is thought proper, taking notice of the 
distance from the meridian, shewn in the equatorial micro- 
scopes, and making allowance, in the reduction, for the mo- 
tion of the sun, or planet, during the interval ; for I esteem 
an observation made within 10 or 15 0 of the meridian, nearly 
equivalent to a meridian observation. But, if an observation 
should be made out of the meridian, the altitude and angle of 
the horary and vertical circles must be taken, by the refrac- 
tion apparatus ; and with these arguments, the refraction and 
parallax, in north polar distance, and in right ascension, may 
be found by inspection, in the tables that follow this account, 
and consequently every observation readily reduced to the 
meridian. 
(32.) 1 shall close this long history with an account of the 
probable accuracy of the observations made with this instru- 
ment, viz. of the amount of the probable errors, derived from 
an experience of more than twelve months. And first, with 
