Refractor to enable it to take part in the International Photographic Survey of the Heavens.
Probably the best example of this type of mounting applied to a refractor is that made by the elder Cooke of York for Fletcher of Tarnbank; the polar axis is of cast iron and the mounting very satisfactory and convenient, but unfortunately no detailed description has been published.
Fraunhofer's chef-d'oeuvre, the great Dorpat refractor, made for Otto Struve about 1820, had a mounting of this type, and was the first equatorial of any importance to be provided with clockwork.
The largest example of his work is the refractor of 24-in.
28, 1843) describes a " heliometre-oculaire " which he made for the great Pulkowa refractor, the result of consultations between himself and the elder Struve.