This counteracted the effects of the Earth's rotation and kept the object in the telescope's field of view. Lassell cast the polar axis in two main sections. This was placed between two stone supporting piers with the lower ball end of the cone resting on a hemispherical recess on the lower pier. It was fixed to the rest of the telescope at its centre of gravity by a heavy cast-iron box which was mounted on the polar axis by trunnion bearings. Lassell had already made a small 9 inch mirror and in 1843 began to make the 24 inch.
Speculum metal is an alloy of copper and tin.
With help from the foundryman James Nasmyth, Lassell made his own equipment to grind and polish the mirror. This gave a parabolic curve accurate to better than a quarter of the wavelength of light, ideal for observing the planets. The secondary mirror was a 45 angled flat made of speculum and mounted on a single arm support inside the main telescope tube. This directed the beam of light from the main mirror out through the side of the tube to the observer's eyepiece. Lassell often found it better to use a prism instead of the mirror.