116 BecKj on a Live-Trap and Parabolic Reflector. 
The facility with which all the parts of this apparatus can 
be taken to pieces and perfectly cleaned is also a feature of 
some importance. 
For general purposes I should propose the following assort- 
ment of the difiPerent parts of this piece of apparatus : — Two 
spring clamping pieces, one with steel and the other with 
silver springs ; three glass plates, about 2^ 4, and 6-lOOths 
of an inch thick, each provided with holes of the re- 
spective diameters of 8, 12, and 16-lOOths of an inch ; three 
black brass plates exactly similar to the glass ones; a few 
thin covers, about 16 by 4-lOths of an inch; (two extra 
ones (Fig. II, c, d) provided with black and ground-glass discs, 
may sometimes prove useful, but the size of these, together 
with that of the holes, may be, of course, varied to suit any 
requirement ;) and the small glass trough, which, together with 
the foregoing, can be completely packed in a small box. 
It will be seen at once that any kind of illumination can 
be employed with the live-trap, and also that the object may 
be examined equally well from either side of the plate, but 
the brass plates, which I have only casually mentioned, pre- 
clude, of course, any Lieberkuhn illumination ; and although 
they are not so easily broken and have some other qualities 
superior to those of glass, I should not have recommended 
them at all but for their answering perfectly well under a 
new kind of illumination^ to which I venture to draw your 
attention. 
In the last number of the Quarterly Journal of Micro- 
scopical Science^ there is a short notice, by Mr. Bridgman, of 
Norwich, showing the advantage that can be gained in the 
illumination of many opaque objects by covering over a portion 
of the reflecting surface of the Lieberkuhn. This plan I have 
adopted for some considerable time ; but I was led to do so 
for an additional reason to that given by Mr. Bridgman, and 
not only, as he says, to obtain any proportion of oblique light in 
one particular direction, but to make sure that I was revers- 
ing the direction of the illumination. The eye habitually 
connects the appearance of an object, and especially that of 
the light and shade, with the direction of the source of light ; 
and as the microscope reverses the picture, the eye may be 
totally deceived in a matter of slight elevations or depres- 
sions, as is well known to many, and as I have lately shown 
to most of you in a simple way, by mounting a photograph 
of a glass tumbler in reversed positions. 
With the binocular body one can almost instantly detect 
any erroneous appearance due to the illumination, but even 
with the use of both eyes it is a most essential thing to re- 
