134 
SECOND REPORT— 1832 . 
In Reichenbach’s circle, the connexion is by three weak joints, 
where a failure of any one will spoil the instrument: and one of 
these is particularly liable to be strained, on account of the 
friction which must in time take place between the two circles. 
I ought not to omit that the Germans consider it a great advan¬ 
tage that the circle is cast in one piece.—It will easily be seen, 
that the use of this circle requires reversion: this cannot be 
done readily (as in the Dublin and Palermo circles), and there¬ 
fore it is only done occasionally. 
I have particularly described this instrument, because it is 
little known in this country, and because it will give a very 
good idea of the peculiarities of the German school of instru¬ 
ment-making. Its distinguishing features are these : 
Telescopes are always supported at the middle, not at the 
ends. 
Every part is, if possible, supported by counterpoises. 
To these principles, every thing is sacrificed. For instance, 
in an equatorial the polar axis is to be supported in the middle 
by a counterpoise : this not only makes the instrument weak, 
(as the axis must be single,) but also introduces some incon¬ 
venience into the use of it. The telescope is on one side of 
the axis: on the other side is a counterpoise. Each end of 
the telescope has a counterpoise. A telescope thus mounted 
must, I should think, be very liable to tremor. If a person who 
is no mechanic, and who has not used one of these instruments, 
may presume to give an opinion, I should say, that the Germans 
have made no improvement in instruments except in the excel¬ 
lence of the workmanship. 
The French repeating circle has lost much of the credit 
which it once enjoyed. Reichenbach’s repeating circles have 
been much used, but in most instances by rejecting the princi¬ 
ple of repetition; which converts them, in fact, into altitude- 
and-azimuth instruments. Of Reichenbach’s universal-instru¬ 
ment, and several others invented here and on the Continent, I 
shall say nothing, because they do not seem likely to produce 
any influence on Astronomy. 
Among those, however, which have been made as auxiliaries 
to the principal instruments, I must not omit to mention Capt. 
Kater’s vertical collimator. The object of this instrument 
(whose construction is too well known to require description 
here,) is to supply a mark which shall be visible like a star, re¬ 
volving in a very small circle round the zenith. By observing 
this in its north and south distances from the zenith, the read¬ 
ing of a circle corresponding to an observation of the zenith 
may be found, and thus the zenith distance of any heavenly 
body may be immediately obtained. Strong testimony has 
