420 JV/r. Pigott’s Determination of 
puted, Shewing the moon’s parallax and motion for fuch devia-> 
tion, which deviation may eafily be found by the well known 
method of obferving ftars whofe difference of declination is 
considerable. 
As travellers very feldom meet with Situations to obferve 
ftars near the pole, or find a proper objeft for determining the 
error of the line of collimation, I Shall recommend the fol- 
lowing idea, which, I believe, has never yet been noticed, and 
hope it will anfwer the purpofe. Having computed the apparent 
R.A. of four, fix, or more ftars, which have nearly the fame 
parallel ©f declination, obferve half of them with the inftru- 
tnent inverted, and the other half when in its right pofition ; if 
the difference of R.A.’s between each let by obfervation agree 
with the computation, there is no error; but if they difagree, 
half that difagreement is the error of the line of collimation. 
The fame obfervations may alfo ferve to determine whether the 
diftance of the correfponding wires are equal. In cafe of 
neceflity, each limb of the fun might be obferved in the fame 
manner, though probably with lefs precifion. By a Single trial 
X made above two years ago, the refult was much more exadt 
than I expedled. Mayer’s Catalogue of Stars will prove of 
great ufe to thofe that adopt the above method. 
In fuch a number of obfervations, it is not furprifing that a 
few Should be erroneous ; I have rejected only three. 
A meridian tranfit of the moon’s limb, Auguft 1 8, 
1782 ; $ Sagitarii was the only Star obferved at York ; it t u 
gives for difference of meridians, . . . 3 55 
Perhaps the ftar has a proper motion, or a miftake 
of one fecond might have been made in marking 
the clock. 
An immerfion of Jupiter’s firft fatellite, June 22, 
3783, which make the difference of meridians, . 3 
1 1 he 
