Seven-feet Transit Instrument. 43 1 
unlike the common balance. The weight is a circular thick 
plate, or short cylinder, and is hooked on to the end of the 
lever ; it is made hollow, with an opening upon it's superior 
edge, allowing small shot to be introduced at pleasure, ac- 
cording as it is wished that the instrumental portion of the 
pivot, as also the instrumental Y piece, should be more or 
less relieved. A reference to fig. 5, Plate XVI. will render all 
this perfectly intelligible. 
Fig. 7, Plate XVII. is a perspective view of the eye end of 
the telescope, in which many of the parts above described 
are differently, and some of them better seen. In it a micro- 
meter is shown, which moves a plate contiguous to that in 
which the five transit wires are inserted ; one wire is con- 
tained in the moveable plate, and is intended to facilitate the 
observations of Polaris, and other juxta polar stars. 
In fig. 6, Plate XVII. on the eastern side of the telescope, 
is seen projecting from it a finger screw ; this gives motion to 
an apparatus within the tube of the telescope, for regulating 
the quantity of light projected from the illuminator upon the 
transit wires of the instrument. 
The instrument was placed upon its piers on the 6th of 
June, 1820, and on the day following a series of experiments 
was begun, to find, if possible, any defects which might 
invalidate the accuracy of observations hereafter to be made 
with it ; the permanency of the side plates, and of the Y pieces 
contained in them, was incessantly scrutinized ; observations 
by reflection and by direct vision were compared ; continual 
reversions of the instrument were made ; constant examina- 
tion of the horizontality of the axis, after every alteration of 
instrumental position, was never omitted ; and the state of its 
