and second
wires (See Phil. Trans. 1827). If an erroneous impression has gone
abroad on this subject, it is doing a service to science to insure its
correction, by drawing attention to it.

Should these observations be confirmed by other observers, it would seem
to follow that the use of a chronometer renders a transit more exact,
and therefore that it ought to be used in observatories.

Among the instruments employed by Captain Sabine, was a repeating circle
of six inches diameter, made by order of the Board of Longitude, for the
express purpose of ascertaining how far repeating instruments might be
diminished in size:--a most important subject, on which the Board seem
to have entertained a very commendable degree of anxiety.

The following extract from the "Pendulum Experiments" is important:

"The repeating circle was made by the direction, and at the expense of
the Board of Longitude, for the purpose of exemplifying the principle
of repetition when applied to a circle of so small a diameter as six
inches, carrying a telescope of seven inches focal length, and one inch
aperture; and of practically ascertaining the degree of accuracy which
might be retained, whilst the portability of the instrument should be
increased, by a reduction in the size to half the amount which had been
previously regarded by the most eminent artists as the extreme limit
of diminution to which repeating circles, designed for astronomical
purposes, ought to be carried.

"The practical value of the six-inch repeating circle may be estimated,
by comparing the differences of the partial results from the mean at
each station, with the correspondence of any similar collection of
observations made with a circle, on the original construction, and of
large dimensions; such, for instance, as the latitudes of the stations
of the French are, recorded in the Base du Systeme Metrique: when, if
due allowance be made for the extensive experience and great skill of
the distinguished persons who conducted the French observations, the
comparison will scarcely appear to the disadvantage of the smaller
circle, even if extended generally through all the stations of the
present volume; but if it be particularly directed to Maranham and
Spitzbergen,--at which stations the partial results were more numerous
than elsewhere, and obtained with especial regard to every circumstance
by which their accuracy might be affected, the performance of the
six-inch circle wil