OBSERVATORY. 
or place, and performs most of the useful 
problems in the science. The following is a 
description of one lately invented by Mr. 
Ramsden, from whom it has received the 
name of the Universal Equatorial. The 
principal parts of this instrument (fig. .g.) 
are, 1. The azimuth or horizontal circle, A, 
which represents the horizon of the place, 
and moves on an axis, B, called the vertical 
axis. 2. The equatorial or hour circle, C, 
representing the equator, placed at right 
angles to the polar axis, D, or the axis of the 
earth, upon which it moves. 3. The semi- 
circle of decluiation, E, on which the te- 
lescope is placed, and moving on the axis of 
declination, or the axis of motion of the line 
of collimation, F. 4. The telescope, which 
is an achromatic refractor with a triple ob- 
ject glass, whose focal distance is 17 inches, 
and aperture 2.45 inches, and furaished 
with six different eye- tubes ; so that its mag- 
nifying powers extend from 44 to 168. The 
telescope in this equatorial may be brought 
parallel to the polar axis, as in the figure, so 
as to point to the pole star in any part of its 
diurnal revolution ; and thus it has been ob- 
served near noon, when the sun has shone 
very bright 5. The apparatus for correct- 
ing the error in altitude occasioned by re- 
fraction, which is applied to the eye-end of 
tlie telescope, and consists of a slide, G, 
moving ill a groove or dove->tail, and carrying 
the several eye-tubes of the telescope, on 
which slide there is an index corresponding 
to five small divisions engraved on the dove- 
tail ; a very small circle, called tlie refrac- 
tion circle H, moveable by a finger screw 
at the extremity of the eye-end of the te- 
lescope; which circle is divided into half 
minutes, one entire revolution of it being 
equal to 3' 18", and by its motion raises the 
c^ntie of the cross hairs on a circle of alti- 
tude ; and likewise a quadrant, I, of It inch 
radius, with divisions on each side, one ex- 
pressing the degree of altitude of the object 
viewed, and the other expressing the mi- 
nutes and seconds of error occasioned bv 
refraction, corresponding to that degree of 
altitude ; to this quadrant is joined a small 
round level, K, which is adjusted partly by 
the pinion that turns the whole of this appa- 
ratus, and partly by the index of the 
quadrant ; for which purpose the refraction 
circle is set to the same minute, &c. which 
the index points to on the limb of the quad- 
rant ; and if the minute, &c. given by the 
quadrant exceed the 3' 18" contained in one 
entire revolution of the refraction circle, 
this must be set to the excess above one or 
more of its entire revolutions ; then the 
centre of the cross hairs will appear to be 
raised on a circle of altitude to the addi- 
tional height which the error of refraction 
will occasion at that altitude. This instru- 
ment stands on three feet, L, distant from 
each other 14.4 inches ; and, when all the 
parts are horizonlal, is about 29 inches 
high ; the weight of the equatorial and ap- 
paratus is only b9lb. avoirdupoise, which are 
contained in a mahogany case. 
The principal adjustment in this instru- 
ment is that of making the line of colli- 
matioii to describe a portion of an hour- 
circle in the heavens ; in order to which, 
the azimuth circle must be truly level, the 
line of collimation, or some corresponding 
line, represented by the small brass rod M, 
parallel to it, must be perpendicular to the 
axis of its own proper motion ; and this last 
axis must be perpendicular to the polar 
axis ; on the brass rod, M, there is occa- 
sionally placed a hanging-level, N, the use of 
which will appear in the following adjust- 
ments : the azimuth circle may be made level 
by turning the instrument till one of the le- 
vels is parallel to an imaginary line joining 
two of the feet screws; then adjust tliat 
level with these two feet screws ; turn the 
circle half round, i. e. 180“ ; and if the 
bubble be not then right, correct half the 
error by the screw belonging to the level, 
and the half error by the two foot screws ; 
repeat this till the bubble comes right ; 
then turn the circle 90“ from the two for- 
mer positions, and set the bubble right, if it 
be wrong, by the foot screw at the end of 
the level; when this is done, adjust the other 
level by its own screw, and the azimuth 
circle will be truly level. The hanging 
level must then be fixed to the brass rod 
by two hooks of equal length, and made 
truly parallel to it ; for this purpose make 
the polar axis perpendicular or nearly per- 
pendicular to the horizon ; then adjust the 
level by the pinion of the declination semi- 
circle; reverse the level, and if it be wrong, 
correct half the error by a small steel screw 
tliat lies under one end of the level, and the 
other half-error by the pinion of tlie declina- 
tion semi-circle; repeat this till the bubble 
be right in both positions. In order to 
make the brass rod on which the level is 
suspended at right angles to the axis of mo- 
tion of the telescope or line of collimation, 
make the polar axis liorizontal, or nearly 
so ; set the declination semi circle to 0“, 
turn the hour circle till the bubble comes 
right ; tlien turn the declination circle tq 
