OBSERVATORY. 
should be erected ; one at Delhi, another at 
Agra, and tlie third at Benares. 
Wanting the use of optical glasses, to 
magnify very distant, or very small objects, 
these people directed their attention to the 
increasing the size of tlieir instruments, for 
obtaining the greater accuracy and number 
of the divisions and subdivisions in their in- 
struments. Accordingly, the observatory 
contains several huge instruments of stone, 
very nicely erected and divided, consisting 
of circles, columns, gnomons, dials, qua- 
drants, &c. some of them of 20 feet radius, 
the circle divided first into 360 equal parts, 
and sometimes each of these into 30 other 
equal parts, each answering to 3', and of 
about two-tenths of an inch in extent. And 
although these wonderful instruments have 
been built upwards ot^ 200 years, the gra- 
duations and divisions on the several arcs 
appear as well cut, and as accurately divid- 
ed, as if they had been the performance of 
a modern artist. The execution, in the 
construction of these instruments, exhibits 
an extraordinary mathematical exactness in 
the fixing, bearing, fitting of the several 
parts, in the necessary and sufficient sup- 
ports to the very large stones that compose 
them, and in the joining and fastening 
them into each other by means of lead and 
iron. 
We have referred to this article from the 
Equatorial, for some account of practical 
astronomy, and the instruments used in this 
branch of science. 
By practical astronomy is implied the 
knowledge of observing the celestial bo- 
dies with respect to their position and time 
of the year, and of deducing from those 
observations certain conclusions useful in 
calculating the time when any proposed 
position of these bodies shall happen. For 
this purpose, it is necessary to have a room 
or place conveniently situated, suitably con- 
trived, and furnished with proper astro- 
nomical instruments. It should have an 
uninterrupted view from the zenith down 
to, or even below, the horizon, at least 
towards the cardinal points; and for this 
purpose, that part of the roof which lies 
in tlie direction of the meridian, in parti- 
cular, should have moveable covers, which 
may easily be moved, by which means an 
instrument may be directed to any point of 
the heavens between the horizon and the 
zenith, as well to the northward as soutli- 
ward. This place, called an observatory, 
should contain the following instruments : 
I. A Pendulum, Clock, for showing equal 
time. This should show time in hours, mi- 
nutes, and seconds ; the observer, by hear- 
ing the beats of the pendulum, may count 
them by his ear, while his eye is em- 
ployed on the motion of the celestial ob- 
ject he is observing. Just before the ob- 
ject arrives at the position described, the 
observer should look on the clock and re- 
mark the time, suppose it 9 hours, 15 mi- 
nutes, 25 seconds; tiien saying, 25, 26, 
iT, 28, &c. responsive to the beat of the 
pendulum, till he sees through the instru- 
ment the object arrived at the position 
expected ; which suppose to happen when 
be says thirty-eight, he then writes down 
9*' 15' 38" for the time of observation, 
annexing the particular day. If two per- 
sons are concerned in making the ob- 
servation, one may read the time audibly 
while the other observes through the instru- 
ment, the observer repeating the last se- 
cond read when the desired position hap- 
pens. 
II. An Achromatic Refracting Telescope, 
or a reflecting one of tw'o feet at least in 
length, for observing particular phenomena. 
See Telescope. 
III. A Mio'ometer for measuring small 
angular distances. See Micrometer. 
IV. A Quadrant, for a description of 
which, and its several uses, we refer to the 
artiele Quadrant. We may, however, 
observe, that besides Hadley’s quadrant, 
which is described there, we have the mural 
quadrant, which is reckoned one of the most 
useful and valuable of all the astronomical 
instruments, and is generally fixed to the 
side of a stone or brick wall, and the plane 
of it is erected exactly in the plane of the 
meridian. There is also a portable astro- 
nomical quadrant, which is in high estima- 
tion, on account of its being capable of 
being carried to any part of the world, and 
put up for the purposes of observation by 
almost any common workman. 
V. Astronomical or Equatorial Sector, 
This is an instrument for finding the dif- 
ference in right ascension and declination 
between two objects, the distance of 
which is too creat to be observed by the 
micrometer. Let A B (Plate Observatory, 
fig. 1.) represent an arch of a circle con- 
taining ten or twelve degrees well divided, 
having a strong plate, C D, for its radius, 
fixed to the middle of the arch at D. Let 
this radius be applied to the side of an axis, 
H F I, and be moveable about a joint 
fixed to it at F, so that the plane of the 
sector may be always parallel to the axis. 
