204 MEMORANDA. 
On the Improvement of the Compound Microscope.—As I have 
bestowed much time, labour, and thought, in the endeavour 
to improve the construction of the compound microscope, I 
avail myself of the pages of your Journal to communicate 
the results to yourself and your numerous readers, 
Ist. It is imperative that the eye-piece be formed of two 
lenses of equal foci, and that they be placed a focal length 
apart. 
Roti These glasses must have as long a focus as can be 
used without interfering with manipulation. 
8rd. The field-glass and objective must be placed at their 
combined focal distances apart. ° 
Ath. The cavity of the eye-piece may be filled with a fiuid 
refractor, so as to represent a solid cylinder of glass cut from 
a sphere. 
The glasses T am using have a focal length of ten inches, and 
the upper focus of the eye-glass is eight and a half inches 
in length, so that my tube measures something within thirty 
inches. The mist, darkness, and dirty London fog, met with so 
generally, are principally owing to the eye-lens having a short 
focal length; if, however, a glass be tried of greater focal 
length than the field-glass, the image will appear very light 
and clear, but with an unnatural glaze. Although a large 
amount of power is lost by equalising the lenses, this is fully 
made up by their long foci, necessitating increased distance 
from the objective. The length of the foci, of course, increases 
very materially the amount of light, which is gained further 
by placing the eye-piece and objective proportionally nearer 
together than is customary—the definition is at the same 
time improved. The introduction of a refractive medium 
between the upper lenses has the effect of magnifying the 
field and image about half a diameter, without shortening the 
foci of the instrument materially. With a simple trd- 
inch lens for object-glass, I have the power of a 1+th-inch 
without the refracting medium, the light of a l-inch; at 
least, an enlarged field definition, equalling, if not excelling, 
that of a simple microscope, and without perceptible change 
of colour—in fact, a most faithful magnified view of the 
object. 
Instruments may be made of length suitable to the stature 
of the observer.—F rep. Curtis, Maryport. 
16th June, 1863. 
Infusoria in Moving Sand.—Mr. James Blake writes as 
follows from St, Francisco, California ;—‘‘ I haye enclosed 
