328 
POPULAR SCIENCE REVIEW. 
dotted lines if continued in solid glass ; but by impinging on the inclined 
polished surface (which is far within the angle of total reflection) they are 
thrown on the flat segmental top ; here they would be totally reflected ahd 
beaten down again to the point, b , outside the cylinder ; but if an object- 
slide, c, be laid over the flat top with an intervening film of water, the rays 
proceed on till the focal point reaches the upper surface or is slightly 
beyond it; here total reflexion now takes place; all the light is concen- 
trated to a minute spot in the centre of the field of view of the microscope, 
and most of the rays are available for any object brought there by travers- 
ing the slides over the water top of the illuminator, which must be kept full 
without allowing any to run down the reflecting surface. It will be seen, 
in order to get the focal point in the centre of the microscope, that the lens 
centre must be excentric ; but this does not involve the slightest inconve- 
nience, as the excentricity only amounts to a little over two-tenths of an 
inch, and is so small that the same adjustment of the mirror serves during 
an entire revolution. The apparatus rotates on the focus as a centre. The 
management of this illuminator is very easy and simple ; its fitting gees 
into the ordinary sub-stage, and has an independent rotary movement of its 
own, like that of Nachet’s prism. The cylinder is brought up nearly level 
with the stage. The centre of rotation is set true by a dot on the fitting, 
seen with a H object-glass. A drop of water is then placed on the top, 
upon which the slide is laid. The required objects on the slide are found by 
a low power, and may be distinguished by their brilliant appearance, while 
those on the cover are nearly invisible. The light is thrown up by either 
the plane or concave mirror. The former is generally the best and most 
controllable. The lamp should not be placed much beyond the stage, else 
its direct rays will get underneath and mar the blackness of the field. 
Having got the best effect, say on a diatom , or insect . scale, by tilting the 
mirror, we now proceed to rotate the illuminator. During this the most 
exquisite unfolding of structure takes place, opening out as it were into 
detail the form of bosses or ribbings. On that superb test, the Podura , for 
example, when the light is thrown from the apex to the quill, the whole 
scale is dotted over with bright blue spots laying in a zigzag direction ; 
these are the most prominent parts or the club-end of the markings, which 
are. nearest in contact with the glass. Fuller details are contained in the 
paper from which these remarks are taken, which should be referred to by 
the reader. — Vide Monthly Microscopical Journal , June 1872. 
The Best Way to see the Markings on Battledore Scales is the following, 
according to Dr. Anthony (“ Monthly Microscopical Journal,” June, 1872). 
He says that scales are best seen by “ transmitted ” ordinary light, when a 
“ pin-hole” stop i s placed like a small cap on the usual wide-angled condenser, 
and by being very particular that both flame of the lamp and object are in 
focus, or very nearly so, at the same time. When scales are looked at by 
“ reflected ” light, then they are to be seen at their best by bringing up a 
little transmitted light at the same time, such light being quite subordinate, 
and only for the purpose of rendering the black shadows transparent. A 
similar effect of course can be got by using a second lamp and “bull’s-eye” 
at the other side of the microscope, or even in a minor degree by a bit of 
white card, placed in the stage beneath the object, so as to reflect light, but 
