The Newtonian Arrangement
For direct photography or visual observations at the focus of the 72-inch mirror, the reflected cone of star light from the mirror B, Fig. 5, is intercepted by a plane mirror also silvered on the front surface, 19·5 inches diameter and 3·25 inches thick placed at 45°. This form of reflecting telescope was first used by Newton, hence the name. The focus is then formed, as shown, at the side of the tube, and if a plate is placed there and accurately guided by small eyepieces with cross wires, photographs of any desired small region in the sky can be obtained, Fig. 4 being made in this position, or visual observations may be made. The oculars can easily be reached from the observing platform for any position of the telescope.