78 CORRESPONDENCE. 
Microscopic CamERA-opscurA.—At page 18 an account is given of a 
method of drawing objects under the microscope, by means of a 
rectangular prism. This method has been in use for a long time. In 
‘Science Gossip” for 1866, p. 233, the following full directions (which 
some of your readers may find useful) are given by Mr. Geo. W. Hart :— 
“‘T remove the cover of the eye-piece, and in place of the camera-lucida 
reflecting-glass I substitute a right-angled prism, fitted in a short tube, 
so that it can be placed close to or removed from the eye-piece for 
adjustment. I have had constructed a wooden frame, exactly like a box 
without a lid. Placing this on a table on end, with the open side next 
the observer, I pass the tube of the microscope through a slit in front, 
this opening being covered with a dark cloth to prevent light entering. 
T also nail another dark cloth on the top of the box, and allow it to fall 
over my head and shoulders; this should be large enough to enable me 
to use both hands. Now, placing the microscope horizontally, and 
putting on the tube so as to throw down a circle of light when the object 
is illuminated, the image will be seen beatifully defined on a sheet of 
paper placed in front of the draughtsman. When it is wished to make a 
coloured drawing, it is well to trace the outline, and then moving the 
paper a little on one side, colour the sketch to correspond with the image, 
which will then be reflected by the side of the tracing. I have used the 
camera in this form for many years, and have wondered that it has never 
been generally used.”—F. Apriu, Hampstead. 
Aquaria.—At page 53, H. M., Derby, asks the best artificial food for 
freshwater fishes when the natural food, &c., is not easily to be procured. 
I beg leave to call his attention to vermicelli; nearly all freshwater 
fish will eat it and thrive thereon. Carp of all kinds take it greedily, 
especially the gold, tench, dace, roach, gudgeon, and minnows, &c. 
Vermicelli has the advantage of being clean, and not discolouring the 
water, as bread does if given too profusely. Of course a little change of 
diet is welcome when it can be got: small red worms or minced raw 
meat; mutton is best, but must be given very sparingly. White fungus 
on carp, roach, &c., is very troublesome, and I think arises principally 
from debility; the fish should be removed as soon as the disease is 
noticed to a separate vessel, if possible. I sometimes take the patient 
out of the water, wipe the fungus off with a silk handkerchief, then 
sprinkle with white sand, and return to the water quickly. The sand 
adhering to the fish causes it to rub itself against stones, &c., which is 
very beneficial. I have had fish quite recover after being treated in this 
way. I can strongly recommend ‘“ The Book of the Aquarium,” by 
Shirley Hibberd, to the notice of H. M.; he will find it a handy little 
volume, and full of practical information, re Aquaria both Sea and Fresh- 
water.—R. G. 
Aquarisa.—Your correspondent (page 53) will find that the small 
crustacea, aquatic larvee, and worms, which may be taken by means of 
a fine net from nearly every pond, pool, or river, are excellent food for 
freshwater fish. If the tank is already sufficiently full of water, take 
some out, and then empty in its place the contents of the can or bottle 
containing your catch of small fry, when it will at once be observed that 
the fish have become very busy in making the acquaintance of their 
newly introduced friends, which they most greedily devour. The spawn 
of snails is also very good food, and may be readily supplied by keeping 
plenty of those interesting creatures as companions in the aquarium. 
Some keepers of aquaria are opposed to the introduction of artificial food, 
as bread, meat, or earthworms; but this will be found to answer well, if 
given in small quantities, and care taken not to leave any uneaten 
portion to decay in the water, which is probably the only source of 
