The best form for mirror reflective telescope is parabolic, i.e., it is the form, which itself takes the liquid surface in a rotating vessel. Designers telescopes spend a lot of busy work to give the mirror a similar form. The manufacture of mirrors for the telescope lasts several years. American physicist wood bypass these difficulties by arranging a liquid mirror: rotating mercury in a wide vessel, he received a perfect parabolic surface, which could play the role of a mirror, because mercury is well reflected rays of light. The telescope wood was installed in a shallow pit.
The lack of a telescope, however, that the slightest push wrinkles liquid surface mirrors and distorts the image, and also that the horizontal mirror gives the opportunity to consider only those lights that are in the Zenith.