There were reflector telescopes whose objective was the surface of liquid mercury. The paraboloidal shape of the lens arises when the fluid rotates around the vertical axis. The focal length of the lens depends on the angular speed of rotation. Currently, such experiments are not carried out due to the fact that mercury is very poisonous.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.