REPORT ON ASTRONOMY. 
135 
been produced as to the accuracy of the results which may be 
expected from using this instrument. 
In the equatorials of Dorpat and Paris, a clock-work motion 
has been given, I believe with great success, so as to keep the 
telescope steadily pointing on the same star. I have not had 
an opportunity of seeing either of these in a state of action. 
Within a few years considerable improvements have been 
made in achromatic telescopes. A telescope of nine inches 
aperture was made by Lerebours: many small telescopes of 
great excellence, and one of more than nine inches aperture 
(for Dorpat), were made by Fraunhofer : two refractors by Cau- 
choix, of eleven or twelve inches aperture, have been imported 
into this country. All these are made on the common princi¬ 
ple of the achromatic telescope. Mr. Barlow has turned his 
thoughts to the construction of telescopes in which the place 
of the flint-glass is supplied by a fluid lens (of sulphuret of car¬ 
bon) : and having succeeded with telescopes of six and eight 
inches aperture, proposes to attempt larger dimensions. I 
believe that none of these surpass in power or clearness the 
twenty-feet telescopes which Sir William Herschel and Sir John 
Herschel were in the habit of using ; but the science has un¬ 
doubtedly gained much by the diffusion of these powerful in¬ 
struments. 
In clocks I do not know of any improvement. Hardy s clock 
is found very useful with transit-instruments, for the loudness 
and sharpness of its beat; but for steadiness of rate it is pro¬ 
bably inferior to the dead-beat which was in general use at the 
beginning of the century. The execution of chronometers 
(without any novelty of principle,) has been very greatly im¬ 
proved. 
In the use of many of these instruments an improvement (as 
I consider it,) has very generally been introduced. It is now 
the rule at many observatories not to attempt mechanically to 
remove all the errors of the instrument, but to measure them 
(which can be done more accurately,) and to apply numerical 
corrections to the observations. This innovation is due prin¬ 
cipally to the Germans. 
III. At the beginning of the century the only good catalogue 
of stars was that of Dr. Maskelyne for 1790. In the last vo¬ 
lume of his observations appeared his catalogue of the right 
ascensions and declinations of thirty-six stars for 1805. These 
were by far the most accurate places that had ever been pro¬ 
duced. The amount of precession (combined for each star, 
with the proper motion of that star,) was determined by com- 
