ON THE EQUATORIAL TELESCOPE. 3 
having its great speculum ] 8 inches, focal length ; a kind of 
telescope by far too unwieldy for circles of the above dimen- 
sions. An engraving, with a brief description of Short’s e<]ua- 
torial, may be seen in Martin’s System of the Newtonian Philo- 
sophy, vol. 3, p. 399, and in the same vol. p. 89, a representa- 
tion and description of the heliostata. 
The late ingenious Mr. Ilamsden, in the construcion of the R.i,„s,ion i 
instrument which he called the Universal Equatorial, seems to 
have considerably simplified Short’s equatorial, and at the same 
time to have rendered it more accurate for astronomical observa- 
tion. This instrument at once serves all the purposes of an 
equatorial, and also for observing particular phenomena in the 
heavens ; having .a telescope furnished with magnifying powers 
extending from *14 to U)8. A figure of this instrument may 
be seen in theKncyclopredia Rritannica, vol. '1, Art. Astronomj'. 
Still, however, this excellent instrument was too expensive to 
be brought into general use; and to this circumstance, perhaps, 
is to be attributed the re.ason, why the equatorial is not as 
generally known as the theodolite, or tlie astronomical 
telescope. 
The most simple instrument I have seen, comprising all the Simplest ai 
apparatus essentially requisite for equatorial movements, is that 
represented in plate 20 of Adams’s Astronomical Essays, 1st 
edition ; but the substitution of plain sights instead of a 
telescope, detracts considerably from its accuracy and general 
use, and prevents its possessor from making many of those 
observations which can only be made by means of an equ.atorial. 
The instrument referred loin the “Celestial Day Observations,” 
published in your Journal for October last, is an improvement 
on that described by Adams, by the addition of an achromatic 
telescope^ and other adjustments; and as the circles are divided 
into 3 minutes of a degree, and 30 seconds of time, it is still 
more accurate than even Short’s equatorial. This instrument, 
however, in its original state, as it came from the maker’s, was 
not fitted for making observations similar to those recorded in 
the article referred to ; as the telescope, though it had an 
C c 2 excellent 
