A description of the method of setting upon the required star, when, for example, photographing the spectra of the stars, will help to make the operation of the telescope more clearly understood. It is easily possible to pull the telescope around by hand to the required star identified by eye among the constellations. Although the moving parts of the telescope weigh nearly 45 tons, so perfect are the ball bearings in which it turns that a weight of 3 pounds at the upper end of the tube is sufficient to set it in motion. However the settings can be much more quickly and certainly made by turning the telescope to the right ascension and declination of the star by the electrical motions. A programme of the stars to be observed with their right ascensions and declinations is prepared beforehand. The observing assistant stands beside the small switchboard on the south pier and rapidly moves the telescope east or west and north or south until the indexes on the graduated circles point to the tabulated positions, while the dome can be turned to the required position at the same time by means of the third operating switch. By pressing two buttons the telescope is then firmly clamped and the driving clock starts the telescope automatically following the star. In the meantime the observer has inserted the plate holder in the spectrograph and drawn the slide and by means of the aluminium switchboard brings the star, which is generally near the centre, exactly to the centre of the finder, when it will be visible on the slit of the spectrograph through a guiding eyepiece and can quickly be brought central and the exposure commenced. The time required from the end of one exposure to the beginning of the next, unless the stars are far apart in the sky, does not generally exceed two minutes, a shorter time than usually required for even quite small telescopes. This rapid operation is due to special care in design and construction and markedly increases the efficiency and capacity of the instrument. Special Features of the Mounting