The Mount Wilson Observatory in California, the first tower telescope worldwide, was the model for the facility designed by Freundlich. In tower telescopes a coelostat (a system with two deflecting mirrors, pronounced "seelostat") at the top of a vertical construction directs light down to an objective. The actual lens system is rigidly integrated into the construction. The mirrors at the top are movable and only these small lightweight instrument components are needed to track the sun. Because of the vertical arrangement, air turbulence near the ground has virtually no effect.