145 
Mr Waddell on a New Optical Instrument. 
picture will be seen more distinctly than with the natural eye, 
and greatly magnified ; and the size of the objects, and extent 
of the field of view, will be regulated by the distance of the in- 
strument from the picture. And when the instrument is used 
as a Compound Microscope, the magnifiers necessary are screw- 
ed into the end of the horizontal tube described at Fig. 1., the 
outer end of which is left perfectly smooth, in order to receive 
another short sliding-tube, fitted as a stage, with spiral screws, 
for admitting sliders of any thickness, with transparent objects. 
When opaque objects are to be examined by this microscope, 
they are placed on a stage, properly illuminated ; and the in- 
strument being placed on the spherical hollow stand, first de- 
scribed, at or about the focal distance of the glasses of the in- 
strument from the object to be viewed, distinct vision may be 
quickly obtained, without any adjustment of the tubes of the 
instrument, by merely moving the flat stand on which it is 
placed gently to or from the object to be viewed. It will be 
seen from the construction of this instrument, that its greatest 
magnifying power as a piicroscope, must be when all the tubes 
are fully drawn out, but that the power may be increased or di- 
minished to a certain degree at pleasure, by shoving out or in 
the said tubes, without any change being made on the glasses 
of the instrument. 
It may be objected to this instrument, that a considerable 
portion of light must be lost by the refractions and reflections 
necessary to produce the effects described. I have not, how- 
ever, found in practice that any material disadvantage arises 
therefrom, as I think the largeness of the apertures made use of 
admits a sufficiency of light tp obviate this defect ; and I have 
not been able to discover, particularly in microscopic researches, 
that the instrument possesses any disadvantages in regard to dis- 
tinctness of vision. 
As this instrument, with the spherical ball of brass and me- 
tallic reflector within the same, is so heavy as to make it not 
sufficiently portable for carrying abroad, to assist in taking yiews 
from nature, I have devised a mode to remedy this, by render- 
ing the vertical tube or tubes of the instrument described under 
Fig. 1 . fit for the purpose. When this tube is unscrewed from 
the upper part of the brass bail, it will be seen, that one of the 
VOL. V. NO. 9. JULY 1821. X 
