COMPENDIOUS ASTROSCOPY.

In an open place, clear on all sides, a mast is fixed into the ground, erected perpendicularly. Ours, which we used first, had a height of fifty feet; sufficient, indeed, for telescopes of 70 feet and more, although not for every ascent of the stars above the horizon. For it ought to be extended not much below the entire length of the telescope. Before it is erected, one side of this is planed smooth with an adze, and two rules are attached there, parallel to each other and an inch and a half apart, thus forming a channel, slightly wider on the inside, which reaches from the top of the mast to almost the bottom, leaving only three feet empty. Furthermore, at the very top of the mast, a small disk is placed, movable around an axis, and a rope is drawn through it, double the length of the mast, and half the thickness of a little finger. And so that one may ascend by it if by chance it is necessary, triangular wooden pieces are fixed at equal intervals, upon which the feet of the climber may rest. Thus the prepared mast is finally erected, with the part that is to be covered by the earth smeared with pitch and surrounded by sand, so that it is less corrupted by rot. The use of the mast is to lift the major lens to a height as far as necessary; which is done in this way.

A small two-foot board is cut on one side so that it can move very freely within the channel we mentioned. In its middle, a wooden arm is attached, extending one foot from the mast, to the end of which another piece, a foot and a half long, is joined at right angles, also at its own midpoint. Both extend parallel to the horizon. The lens is placed upon this transverse arm in the way we will describe, and everything is pulled upward by attaching the ends of the small board to the rope demonstrated before; which, ascending from the bottom of the mast to the top, and passing over the small disk, descends again from there, and, before it reaches the ground, is tied into the other end of itself. This rope has a lead weight attached to it, equal in weight to the movable arm with the lens placed upon it, and it remains in that place. Thus, it is very easily raised to the required height, and, when the rope is released, it remains suspended there of its own accord. The shape of the lead weight ends on both sides in the point of a cone, so that it does not catch on the triangular pieces which we said were fixed through the mast.

Moreover, this major lens of the telescope is positioned and adjusted in this way.