G. Calver, while introducing the list of prices below, has the
greatest confidence in calling the attention of the practical
astronomer and the amateur to the very moderate prices charged,
considering the principle and style of the mounting, and the firm
and well-fitted arrangements in all the parts.
The principle of the mounting is that which is the most convenient
to use, and with the greatest degree of steadiness with the easiest
movements. Fig. 1 is the _best mounting ever applied to the
Reflecting Telescope_.
He is also able to state that, with his processes and special
facilities for working large specula, and substantially mounting
them, he is prepared to construct automatic equatorials of large
sizes, and with any special arrangements that may be required.
Fig. 1 is a very excellent mounting, and admirably suited for large
instruments, especially when clock-power is applied; and as now
manufactured by G. CALVER, is the most complete and reliable, its
details of construction being such as to give the greatest freedom
of motion and steadiness. For large sizes the top of polar axis
works on friction rollers; and, as a superior German stand, its
arrangements and means of astronomical as well as optical
adjustments, are such as to make it an instrument of precision.
To ensure these qualities many well considered
arrangements—entailing careful and expensive workmanship—must be
provided; details that do not easily admit of description in an
ordinary catalogue, or can be shown in an engraving, but are duly
appreciated by the observer, who will find their value by practice.
The cradle bar is compound with fine screw movement for perfecting
collimation, but to make this adjustment perfect, the telescope tube
must be centred in a powerful lathe, and the cradle and solid metal
rings in which the tube revolves (see illustration) has to be turned
and fitted with true flanges or working bearings; the mechanical and
optical centres will then coincide.
The hour circle, to be truly divided, must be truly made, and is a
solid wheel of good substance, working on a secondary axis, and
rotated by mechanical means, truly concentric, with a very strong
polar axis.
The declination circle has fine tangent screw movement, with double
action for setting the readings by milled-headed screw, and also
long driving rod from the eye-piece to set and adjust the object in
centre of field. There is slow hand motion, by a separate wheel in
right ascension.
The clock-power is connected and disconnected instantly, by touching
with the finger a small lever, conveniently placed at a small door
in the clock case. The clock will go at exactly the same rate,
whether it is driving the telescope or not, and the latter begins to
move at the proper speed the instant the lever is moved, and the
connection of the telescope and clock made, which is instantly
effected by another lever.
£ s. d.
14, 15, to 16 inch Speculum mounted as (Fig. 1), with
rotating hour circle reading to 5 seconds and decimation
to 1 minute (the diameter of the circles never less than
that of the Speculum, and often larger)
8 powers, from 50 to 700, with first-rate and very powerful
driving clock, first-class instrument,
and complete from £250 to 350 0 0
17, 18, to 20 inch Speculum, with 10 powers, from 50 to 800,
including Kellners, Huyghenians, and Achromatics,
from £360 to 500 0 0