H. Sxry.—An Astronomical Telescope on a New Construction. 123 
eye-piece through an aperture left in the plane reflector. This is perforated to 
allow of a small telescope or finder to be used, or the finder can be placed at 
the side of the mirror as in Fig. 4. Let both plane mirror and finder bave 
a vertical motion on a horizontal axis common to both, then since “the angle 
between the first and last direction of a ray of light suffering two reflections in 
the same plane, is twice the angle of the reflecting surfaces to each other,” 
and because the first direction of the ray is the same as the finder, and the 
last direction is towards the zenith, it follows that the angular motion of the 
finder must be twice that of the plane reflector ; this is easily accomplished, 
and in such a manner that by merely turning the finder on to an object the 
reflector shall move through its proper angle. 
Bry Let AA (Fig. 4) represent a plat- 
form fixed above the speculum, H is a 
rod working an endless screw which 
turns a horizontal racked wheel, B, 
rotating on rollers running in grooves 
between the platform and the wheel, 
This wheel carries the pillars II, con- 
sequently the mirror, C, and the finder, 
D, move in azimuth with equal veloc- 
ities. The mirror is firmly braced on 
to the tube, TT, which carries with 
it the wheel, E, and E turns another 
broad wheel, F, which turns with the 
same speed as E, for that part of it 
which receives motion from E is equal 
to E. The other part of F has such a 
diameter as will give a motion to the 
S wheel, G, of double the velocity of E. 
Fig. 4. The ratios of the diameters of these 
wheels are E=6, small part of F=6, large part of F=8, and small wheel 
G=4. The dotted line represents a strong rod or axis, which also goes 
through the tube T. To this axis the wheel, G, and the finder, D, are firmly 
keyed. The finder is attached to, and moved in altitude by another racked 
wheel, also turned by an endless screw, K ; then, whatever angular motion in 
altitude is imparted to the finder, the mirror shall receive one-half thereof. 
The eye piece is fixed near E, and is supported by connection with the pillars 
so as to be independent of any vertical motion of the mirror. 
Such an arrangement gives the same degree of illumination as is given by 
the Newtonian telescope, there are two reflections, with this difference, that 
the light from the object is first received on the plane mirror instead of on 
