. The Encyclopaedia Britannica; ... A dictionary of arts, sciences and general literature . by employing a driving arc gets the telescope much closer to thopolar axis with an increased radius for driving, and he makes thepolar axis a very largo hollow steel or cast-iron cylinder in whichtorsion is insensible. Both Grubb and thoRepsolds seem to think that for the tube ofthe telescope all necessary rigidity canhe attained with cylindrical tubes ofriveted steel, the thickness of thesuccessive sheets of which dimin-ish from the centre-piece out-wards without makingthe extremities cone-shaped. In t
. The Encyclopaedia Britannica; ... A dictionary of arts, sciences and general literature . by employing a driving arc gets the telescope much closer to thopolar axis with an increased radius for driving, and he makes thepolar axis a very largo hollow steel or cast-iron cylinder in whichtorsion is insensible. Both Grubb and thoRepsolds seem to think that for the tube ofthe telescope all necessary rigidity canhe attained with cylindrical tubes ofriveted steel, the thickness of thesuccessive sheets of which dimin-ish from the centre-piece out-wards without makingthe extremities cone-shaped. In these verylarge tele-scopestho. Fia. 23.—Grubbs mounting for the Lick object-glass,arrangements for giving access to the eye end and for followin itsdiurnal motion have hitherto proved a source of difficulty. Thetravelling stages of the new Pulkowa telescope are the most man-ageable and practical that have yet been contrived, but even theyleave much to be desired. For energetic work the standing posi-tion is best, provided that the eye-piece is situated at the preciseheight above the stage whicl; ia most convenient for the observer,and that the altitude of the observed object is not greater than60°. For altitudes above 60° a small chair with a back, the topof which is stuSed for tho head to rest upon, is the bcrt seat,provided that .the observers eye can be kept at the height ofthe eye-piece. Accordingly Grubb has suggested the followingplan for the observatory at Mount Hamilton, California, whichis to cover the Lick telescope. The whole floor, 70 feet in dia-meter, is to be raised or lowered by water-power unde
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