Opaque Objects with High Poivers. Bg G. W. Moorehouse. 31 
of an inch.” Evidently this means dry-working objectives. A 
few gentlemen have used it with immersion objectives. When an 
immersion lens is used, the whole aperture of the objective is avail- 
able, both as a condenser and an objective, for the light passes 
through the glass cover to the object without reflexion from the 
upper surface of the cover, as would be the case with all rays 
striking the cover at an angle of total reflexion, if a dry front was 
used. 
I have used this illuminator with excellent results with Tx th 
and -g^th immersion objectives, with lamp as described above. Im- 
proved effects may sometimes be produced by introducing the hand 
or a diaphragm between the lamp and reflector, cutting off a 
portion of the light, and such tests as Pleurosigma Spencerii and 
Navicula rhomboicles may be well resolved. 
The object should be mounted dry, and in close contact with 
the covering glass, so that the extreme oblique rays will pass to it, 
and not be reflected from the lower surface of the cover. The 
usual care must be taken in correcting the objective for thickness 
of cover. 
I append selected memoranda of observations to show the 
utility of this mode of using the microscope, and venture to pre- 
sume that no one will deny the general trustworthiness of illumi- 
nation by reflected light, or the fact that errors of interpretation 
are less likely to creep in with it than with ordinary transmitted 
light. Objects are seen in their natural colours, and the views 
obtained of such specimens as the scales of insects are indeed 
beautiful. This is also true of numerous other objects. 
The scales of Macrotoma major, Lepisma saccharina, Deegeria 
domestica, and Lepidocyrtus curvicollis, I have been able to see 
better, and the true character of the markings more satisfactorily 
indicated, than by any other method of illumination. It may not 
be out of place to state the fact that no semblance of the so-called 
beading is to be seen on any of them. The Macrotoma and 
Lepisma, like the scales of the gnat, show only the longitudinal, 
or, as the case may be, radiating ribs, with the transverse and often 
irregular and waved corrugations or wrinkles. The smaller scales 
of any of the insects named show almost as easily and distinctly as 
the larger, the resolution is so much superior to that ordinarily 
employed. With the Tolies immersion, 3 Vth powers of x2500 and 
x4000 were employed ; and with Tolies’ four-system x Vth, x500, 
xlOOO, x2000, and x4000, the last two by using ^-incb and £-incli 
solid eye-pie > The objects were well defined, with enough light, 
even with the highest powers used. 
The Deegeria scales are covered with short or interrupted ribs, 
or long spines, adhering to the surface of the scale ; a structure 
intermediate between the true ribs of the Ma-iotoma and the short 
VOL. XVIII. D 
