Dr Brewster on a New Reflecting Microscope. $27 
burgh Encyclopaedia (vol. xiv. p. 224.), is the Cassegrainian tele- 
scope in an inverted form. In like manner, the microscope 
which I intend now to describe, is an inverted form of the re- 
flecting telescope, described in vol. vii. p. 823. of this Jour- 
nal. 
This microscope is represented in Plate VII. fig. 16., where 
ABCD is a tube supported horizontally, upon a stand ST, 
with a draw tube E containing an eye glass. An ellipsoidal 
speculum AB, having its two foci at F,yj is placed at the other 
end of the tube, and an achromatic prism GH, constructed in 
the manner described in this Journal, vol. vii. p. 826., is placed 
between the mirror AB and its nearest focus E. An arm KL, 
projecting from the stand ST, carries at its end K an inclined 
ring, for holding the object sliders, and the object, such as m n, 
may be illuminated either in front, if it is opaque, or by a mir- 
ror below, if it is transparent. 
When the distance of the object mn from the prism GH is 
equal to the distance of the prism from F, the refraction, by the 
prism, of the rays proceeding from the object a b , will make them 
fall upon the speculum AB, as if they had proceeded from F, 
and a magnified image of it will be formed in the other focus 
which will be again magnified by the lens or lenses placed at E. 
The advantages of this microscope may be estimated in ex- 
actly the same manner as has been already done, when we de- 
scribed the analogous combination in the form of a telescope. 
The prevention of the loss of light by reflection from the se- 
cond speculum is the chief advantage of this construction, and 
has been already fully explained. 
When reflecting microscopes are constructed on a very large 
scale, as recommended in a former article (see this Journal , 
vol. vi. p. 105 ), the small speculum, or the glass prism, may 
be entirely dispensed with, and the whole effect may be pro- 
duced by oblique vision, as in the large telescopes of Sir Wil- 
liam Herschel. 
Edinburgh, | 
Mar. 4. 1828. j 
