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POPULAR SCIENCE REVIEW. 
the tympan, and the apron has moved from beneath, and gone forward to 
discharge the nonmagnetic portion of the ore at the foot of the machine, the 
tympan is momentarily withdrawn a short distance from the poles, and the 
adhering magnetic ore falls in the open space, between two aprons, into a 
receptacle placed below. This process of loading and unloading the magnets, 
can be repeated sixty times in each minute. 
MICROSCOPY. 
The Beading of Diatomacece is well described by Mr. Henry J. Slack, Secre- 
tary to the Microscopical Society, in the “Monthly Microscopical Journal.” 
Mr. Slack says that the uniformity of plan in the silicious deposits of diatoms 
is to a great extent shown, and to p still further extent suggested, by examin- 
ing one of M oiler’s admirable “ type slides,” with a good immersion £th or 
higher power. The gradations from large beads distinctly separated, to 
smaller beads closely approximating, are readily and instructively exhibited, 
so that it is easy to trace a series, beginning with large forms that present 
no difficulty of resolution, and concluding with the most delicate that tax 
the utmost power of the optical apparatus. When beading appears minute 
under high magnification, and each bead seems in contact with its neighbour, 
the outline of a section made by a plane passing through the bead rows 
perpendicular to the uppermost point of their circumference, would exhibit 
a delicate wavy line, the depressions of which would be extremely small, as 
they would correspond with the radii of the little spheres, while the width 
of the curves would correspond with their diameters. All that can be done 
under these circumstances, by the best adj ustments, and the most careful 
unilateral illumination, is to exhibit minute, and often very faint, alterna- 
tions of light and shade, indicating rather than demonstratively showing the 
character of the structure. When the best has been done with any 
objective, it becomes evident that a slight increase of the difficulty, from 
greater minuteness of the structure^, would render it invisible, and make the 
surface look plane. 
Tolies' Binocular Bye-piece. — Professor Smith has written to the “ Monthly 
Microscopical Journal,” explaining that he is not the inventor of this instru- 
ment. He exhibited it here, and hence the mistake arose. It is really Mr. 
Tolies’ invention. Mr. Smith says that Dr. Carpenter has made a mistake 
as to the inventor of it. 
An Erecting Mirror , which is made to surmount the eye-piece, has been 
devised by Mr. C. Richards. It consists of a glass reflector, platinised on 
the front surface, thus getting rid of the second image, always seen when an 
ordinary silvered surface is employed. The dissecting needles or knives are 
not reversed by it, as might have been expected ; for after having adjusted 
the focus, by simply turning the mirror on its axis one quarter from the 
right hand, the needle held in the right hand is immediately brought into a 
proper position. The definition or perfection of the image is in no way 
impaired, and therefore it will be found useful in drawing as well as dissect- 
ing. — Monthly Microscopical Journal, November. 
