Riding the wave

Bamberg's Transit Telescope

The instrument consists of a telescope that can rotate around a horizontal axle, the latter being not at mid length of the telescope, and also having the eyepiece not aligned with the objective: the light through the lens is reflected, at the axle and along it, towards one end where the eyepiece is located.

This type of frame (called a broken telescope) is convenient because the viewer's eye is always at the same level, regardless of the height of the star observed; it also makes it more compact, because it allows to shorten the support axle, while allowing the movement of the telescope along the whole celestial meridian.

This arrangement had been invented by Baron Zach, who in 1811 had proposed it to Reichenbach for implementation. The first model was sent to Zach in 1815, when he was in Naples; after a while, Barnabas Oriani also bought a similar device.

The axle is formed by two truncated cones, and rests on two vertical frames shaped like a "A", that are integral with the rectangular base.

The latter is supported, by three pins, on a triangular base. Two pins, those along the short side of the triangle, end on two plates that, by means of set screws, can slide along a groove on the base: the whole support can thus be rotated horizontally around the third pivot, so as to properly orient the axle.

The triangular base has three legs with leveling screws that allow to level it horizontal. The levelness of the instrument is verified by means of small spirit levels; two, at right angles to each other, are on the triangular base, another one is on one of the "A" frames. To accurately check the levelness of the axle, there is a long spirit level, hanging under the axle by two support hooks.

Another spirit level is fastened perpendicularly to the axle, by means of a collar, and its weight is balanced by a counterweight, symmetrically placed with respect to the axis.

The reversal of the instrument is very simple. By moving a lever, two vertical supports rise the axle of the instrument, lifting it from its supports: they can then rotate around a vertical axis, until each end is over the opposite stand, where the instrument is lowered by releasing the lever.

The eyepiece is at one end of the horizontal axle. At the same position there is also a ring for pointing the telescope; it is divided into intervals of 20 primes (figure indications every 10 degrees) and a vernier allows to read a minimum interval of 1 prime. The sliding end of the vernier has, on the opposite side, a spirit level with a mirror. The eyepiece is fitted with an impersonal micrometer.

(Text taken from The instrumentation in the history of the Astronomical Observatory of Brera , Milan University, 1989)
Bamberg's Telescope

A Bamberg's telescope, with an engraving on the the base saying "Carl Bamberg - Friedenau - Berlin No. 7904", is located at the Hydrographic Institute of the Navy and was placed in the observatory of the Institute.
By Paola Presciuttini