MICROSCOPY. 571 
is found, slightly above their surface, and in the focus of each is 
seen the image of an object, as for instance a fly on the point of a 
pen, held between the stage and the mirror. By a little ingenuity 
a good view can be obtained of a blind-tassel, the profile of a 
person standing before the window, or even of a landscape out- 
side; though these distant and difficult objects show better by 
using a } inch objective and a one inch lens as achromatic con- 
denser. A swinging tassel, or a profile cut in brown paper and 
fastened against the glass, or a person’s hand with the fingers in 
motion, or a watch face with the second hand in motion, are 
among the curious or grotesque objects that may be seen multi- 
plied hundreds of times in the beetle’s eye. When lamplight is 
used, it must be rendered parallel by the bull’s-eye, and for really 
good effects the concave mirror and one inch achromatic condenser 
must also be used. ; 
BocurLars ror Hrem Powers.— Mr. Wenham, finding the 
various non-stereoscopic binoculars unsatisfactory, and finding it 
inconvenient to make and mount a reflecting prism which should 
come sufficiently near the lenses to be efficient with the highest 
powers, has revived the achromatic refracting prism suggested by 
him to the Microscopical Society on June 13, 1860, by which the 
rays from each lateral half of the objective are bent towards the 
axis of the tube, crossed, and sent to the opposite eye of the ob- 
Server. The prism, representing really two prisms cemented back 
to back, is made so small and mounted in so thin a tube that it 
can be slid down into the mounting of the objective close to the 
posterior lens. 
Structure or Evropiscus anp Istamra. — Mr. Henry J. Slack 
has communicated to the Royal Microscopical Society some im- 
portant researches on this subject, tending to confirm his previous 
impression that in all diatoms the silicious deposition takes place 
in spherules of varying dimensions and arrangement. He entirely 
discards such terms as ‘‘areole,” “cellules,” etc., believing that 
Such apparent structures are merely, and always, unresolved groups 
of variously aggregated spherules. This structure he has demon- 
strated, and has repeatedly confirmed on Pinnulariz, but with the 
old means of investigation he failed on Isthmia and Eupodiscus. 
ith Mr. Wenham’s new “Reflex Illuminator,” however, these 
easily fall under the same law, the circular valve of Hupodiscus 
