SCIENTIFIC SUMMARY. 
217 
dense flint glass lens. Tlie three lenses are united by a transparent cement 
which has a refractive index corresponding very nearly with the glass. This 
prevents light being lost by reflexion from the surface of the deep curves. 
The new lens is manufactured by the inventor, Mr. J. Browning, the opti- 
cian, of 111 Minories, E.C. 
Diatomacece - to be Obtained from Coal. — The li Monthly Microscopical 
Journal” says that the following method of' obtaining the diatomacese 
from coal for the microscope is described by Count Castracane : — “ The 
course to pursue is decided by the flinty nature of the diatom valves, 
and in order to separate them from the mixture of calcareous or organic 
matter with which they are found united, it is usual to put the whole into a 
glass test-tube with hydrochloric acid, adding chlorate cf potash from time to 
time, keeping all slowly dissolving by heat, in order to isolate the silex, 
destroying the remainder. But in unburnt coal it is too difficult to dislodge 
the carbon, and the acids have little effect upon it. I must, however, refer 
to the calyination I effected by grinding up the substance, and then, collect- 
ing it in a china vessel, placed upon a stove in a glass tube, subjecting the 
whole to the action of the heat, while, at the same time, a slight current of 
oxygen crossing the tube combined with the carbon in creating acid. Ex- 
perience has taught me, however, the necessity of conducting this operation 
at a lower temperature, in order to prevent the alkaline or earthy bases and 
metallic oxides, which may be amongst the ashes, from forming vitreous 
silicates by melting and mixing with the valves of the Diatomaceee. It is 
also well to leave the glass tube, in which the fusing is going on, uncovered, 
in order to watch its progress. The small residue obtained through this 
process is to be put into a clean test-tube, adding nitric acid and hydro- 
chloric acid and caustic potash, assisted by the heat of a lamp, to eliminate 
any alkaline or earthy base and every trace of metallic oxides. The last 
operation over, it only remains to wash rapidly with distilled water the very 
light dust which is left behind, letting it stand for some hours to settle, in 
order to be sure of not losing the smallest particle of it in pouring off the 
water. Those who follow this method exactly cannot fail to succeed. The 
object may then be mounted with Canada balsam, or in any other suitable 
medium ; and steadily and closely watching it, under the microscope, they 
will not be long before they see some valves of diatoms, entire or broken.” 
The Leaf Glands of Saxifraya tridactylites. — The u Monthly Microsco- 
pical Journal ” of Jan. says that an addition to our list of carnivorous plants 
is suggested by Mr. J. C. Druce, in a letter to the u Pharmaceutical Jour- 
nal,” in a little early spring flower found chiefly on the tops of walls, 
Saxifraya tridactylites , a plant not very distantly allied to the Droseras. 
Mr. Druce states that when examined under the microscope the leaves are 
seen to be covered with glands of a similar character, which exude a viscid 
secretion, in which he found a midge was entrapped and held fast when 
placed on the leaf. On examining a number of leaves, he found in all of 
them the debris of insects which had apparently perished in this manner. 
Mode of lookiny at a Watch throuyh a Beetle's Bye. — Dr. Whittell, of 
Adelaide, Australia, has a paper on this subject in the “ Monthly Micro- 
scopical Journal,” March, in which he gives the following instructions as to 
the mode of mounting the specimen : — Take a watch with a white face, take 
