There is an objection to the form of instrument given above,—the telescope cannot be pointed to any position near the pole, since the stand comes in the way. This is obviated in the various methods of mounting, which we shall now pass under review.
The German Mounting.
This is the form now almost universally adopted for refractors and reflectors under 20 inches aperture.
The polar axis has attached to it at right angles a socket through which the declination axis passes, and this axis carries the telescope at one end and a counterweight at the other. The polar axis lies wholly below the declination axis, and both are supported by a central pillar entirely of iron, or partly of stone and partly of iron.
By the courtesy of Messrs. Cooke and Sons, Mr. Howard Grubb, and Mr. Browning, we are enabled to give examples of the various forms of this mounting now in use in this country for instruments of less than 20 inches aperture.
In Fig. [138], we have the type form of Equatorial Refractor introduced some 30 years ago by the late Mr. Thomas Cooke. The telescope is represented parallel to the polar axis, which is inclosed in the casing supported by the central pillar, and carries one large right ascension circle above and another smaller one below, the former being read by microscopes attached to the casing.
The socket or tube carrying the declination axis is connected with the top of the polar axis. To this the declination circle is fixed, while an inner axis fixed to the telescope carries the verniers.
Fig. 138.—Cooke’s form for Refractors.
