404 Progress in Science. (July, 
Microscopy.—Count F. Castracane (‘Der Naturforscher”) has demon- 
strated the existence of Diatomacez during the coal period. His first objec 
of investigation was a piece of Lancashire coal, which was pulverised, and 
then exposed to a white heat. The decarbonised dust was then treated with 
nitric acid and chlorate of potash in test-tubes, and washed clean with 
distilled water, and then placed under the microscope. The Diatomacez 
found in this coal belong, with the exception of a Grammatophora, of a small 
Coscinodiscus, and of an Amphipleura, entirely to fresh-water genera and 
species, such as the following :—Fragillaria Harrisonii, Sm.; Epithemia gibba, 
Ehbg.; Nitzschia curvula, Kz.; Cymbella scolica, Sm.; Synedra vitrea, Kz. ; 
Diatoma vulgare, Bong. The presence of the marine forms which were 
present among the very numerous fresh-water diatoms, only in one single 
specimen, appears to prove that, at one time, even sea-water found its way 
among the vegetation from which the coal originated. Besides this Lanca- 
shire coal, Count Castracane investigated coal of the carboniferous era from 
other localities, e.g. a piece of the so-called Cannel coal from Scotland, from 
Newcastle, and from the mines of St. Etienne. In every one of the pieces 
the presence of Diatomacez in greater or less numbers was proved. The 
species varied in the three different specimens of coal, but, as in the case of 
the Lancashire coal, not even a single new form was discovered, but all 
closely agreed with the existing fresh-water Diatomacez, from which they 
could not be distinguished by the most practised eye; all the signs by which 
the species of Diatomacee are generally distinguished are, in the Diatomaceze 
of the coal period, identical with those of existing species; so that these 
organisms, in the indeterminably long period from the coal epoch to the 
present time, have undergone no perceptible modification. 
Mr. Wenham communicates to the Royal Microscopical Society (March 3, 
1875) an easy method of obtaining oblique vision of surface structure under 
the highest powers of the microscope. As the closeness of the high powers 
to the covering-glass will not permit the slides to be tilted to an extent to 
cause any appreciable difference in the appearance of an objed, the following 
arrangement is to be adopted :—a is a slip of glass about ;4;ths of an inch 
wide, ground and polished off to an angle. Objects to be mounted, such as 
diatoms or lepidopterous scales, are scraped up with the knife edge, so as to 
be distributed thereon along the sloping plane. ‘Those situated near the edge 
may be viewed with the highest powers, as the glass is of course thinner here 
than any cover. The thickness of the remainder of the prismatic slip is of no 
consequence, and it may be of the same gauge as an ordinary thin slide. The 
slip is tacked on to a 3 x1 slide with a dot of balsam or cement. Another 
similar slip b is then pressed endwise against it, so as to lay the objects flat 
between the two inclines. The lower prism is necessary, for without it a 
deal of offensive colour enters the objeét-glass from the decomposition of the 
transmitted light. This is recomposed or neutralised by the under prism, 
which also greatly increases the obliquity of the illuminating ray by refracting 
this to the same angle as that of vision, from the deflection of the axial ray 
of the object-glass. The degree of inclination of the facets of the prisms 
should be less than 40°, for on holding before a flame a slide having this 
angle, and tilting it slightly, the width of the junction of the prisms appears 
as a dark band impervious to light—the effect of total refleion. About 35° 
is therefore more suitable for objets mounted dry. If balsam is run in 
between the inclines, of course total reflection is eliminated and refra@tion 
nearly so, and we then see the object at an angle the same as the incline ; 
therefore for objects in balsam 45° would be preferable. In using slides with 
