A Combination Telescope and Dome

By a curious coincidence this form of telescope mounting was completed in its essentials on the day in which the writer first heard of Sir Howard Grubb's "aquatic" mounting for a reflector.' The two mountings have features in common, of which the most important is an attempt to procure rigidity of support and steadiness of movement. Complaints of unsteadiness while using the microm eter are common against the ordinary form of mounting. This instability is due to irregularities of the clock movement and lack of rigidity in the mounting. A slight wind beco mes a most annoying visitor and an accidental touch sets the tube vibrating in a most aggravating manner. The first idea in the development of the spheri~al telescope (a provisional name adopted here for convenience) was that much movement could be eliminated by applying the motive power near the eye-end of the tube. Still further stability would be insured if the tube were held at each end instead of at the middle. The final step was to place the tube inside a sphere mounted like an ordinary globe. The following pages will present various mechanical difficulties of the plan and suggest solutions. As a matter of convenience the dimensions recommended will be such as might apply to a sphere I oo feet in diameter and a lens of seventy-two inches.J The sphere floats on water which is confined in a circular cistern of sufficient diameter and depth. At the bottom are several supports upon which it can rest whil e in process of construction or repair. Its normal position would be less than one · foot above these. The sphere itself should be made of thin st eel, well braced. It is not necessary that it should have a perfectly ' In New York World (about) November I I, I894· For origi nal article see J{n1wl-edge for May, I894· 40I