176 Captain Kater's description of 
little distance from this aperture, the telescope is to be 
securely fastened to the wall in the direction of the zenith. 
This may perhaps be conveniently done by two irons driven 
into the wall, terminating in rings, into which the telescope 
may be passed and clamped. A box of sufficient size to 
contain the floating collimator being prepared with a circular 
aperture in the bottom of it, a very little less than that in 
the shelf, a piece of tube made of sheet iron, varnished brass, 
or even tinned plate, well painted or varnished, of a size 
to fit very tightly * into the aperture of the box, must be 
passed into it and secured so as to project above the bottom 
on the inside an inch or two, and on the outside two or three 
inches more than the. thickness of the shelf. The part of the 
tube outside the box must be passed through the hole in the 
shelf, and the box may then be readily turned about the 
axis of the tube as a centre. The side of the box being placed 
nearly in the direction of the meridian, its position must be 
determined by a pin driven perpendicularly into the shelf, so 
as to come in contact with a pin projecting from one corner 
of the box near the bottom, and in the direction of one of its 
sides. The box is then to be turned half round in azimuth, 
and a pin is to be fixed in the opposite end of the box in con- 
contact with that in the shelf. By this contrivance, the box 
may be turned at pleasure half round the azimuth. 
The float should be of cast iron, with a hole in the middle 
an inch larger in diameter than the tube. It is to be fur- 
nished with pins, and the box with corresponding grooves 
to steady it, as before described. An arm of plate iron is to 
be fixed to the float, its edge being at right angles to the 
surface. This arm is to project over the aperture, and to ter- 
minate in a small tube at the centre, to receive a telescope not 
