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LXIII. On a Method of fixing a Transit Instrument exactly 
in the Meridian. By F. Baty, Esq. F.R.S. @ L.S.* 
Tu E transit instrument is so essential a part of the apparatus 
of the practical astronomer, that every attempt to facilitate the 
use of it will doubtless be received with indulgence. When 
this instrument has been brought early in the plane of the me- 
ridian (which may be done by any of the methods pointed out 
in the several works on practical astronomy), it may be adjusted 
accurately by either of the following modes: 1°. by observation 
of the pole-star, at the time of its upper or lower culmination : 
2°. by observing any of the circumpolar stars at the time of their 
upper and lower culmination; and 3°. by observing the culrni- 
nation of any two stars differing from each other considerably in 
declination. The two former methods (independently of their 
requiring a building peculiarly constructed so as to command an 
uninterrupted view of the meridian, from the northern to the 
southern horizon) are liable to some objections, to which it is 
not my intention at present to advert: but the latter method 
may be practised in every situation in which a transit instrument 
may be placed, and as the results are extremely correct, I shall 
confine my remarks to this mode only of adjusting the instru- 
ment. Moreover, there are many persons, fond of practical 
astronomy, who have not the convenience, or who do not wish 
to incur the expense, of constructing a building of the kind above 
mentioned ; and who are therefore compelled to fix their transit 
instruments on the sill of one of their windows, or in some other 
similar situation: many, again, who are travelling, with a view 
to improve the connected sciences of astronomy and geography, 
are obliged to fix their transit instruments in the most convenient 
and safe situation, where their prospect may be confined toa 
_ southern aspect :—to all such persons the method here alluded 
to, is the only one which can be adopted. Portable transit in- 
struments, adapted to such purposes, are now made with great 
neatuess and accuracy, and of various sizes; and are a valuable 
addition to every ceconomical observatory, and to every person 
travelling for the purposes above mentioned. When placed on 
the inner sill of a window, they have a range of above 70° in al- 
titude ; and when placed on the outer sill, they may be pointed 
even to the zenith. 
I shall therefore suppose that an instrument of this sort has 
been brought nearly in the plane of the meridian, by any of the 
known methods for that purpose: after which it may be accu- 
rately adjusted by determining its deviation from the meridian 
* From the Memoirs of the Astronomical Society of London. 
Vol, 59, No. 288, April 1822, 1g by 
