THE YOUNG SCIENTIST. 
19 
fruit and the very tendrils, swarmed myriads 
of creeping things, flocks of aphides tended by 
their herdsmen the ants, vine sappers, lady 
bugs, crickets, etc. Was it not the easiest 
thing in the world for some of them to tumble 
into the tub ? Then there were thousands of 
anxious mother mosquitoes looking for just 
such a watery spot on which to construct and 
launch forth their egg boats ; could minnows 
ask for finer food than fresh laid mosquito 
eggs? Audit is not improbable that a mos- 
quito herself would sometimes be gobbled up 
as she rested on the water, in the act of con- 
structing her egg boats. As for. the sun, he 
shone on the tub one hour every morning, 
which was sufficient for so confined and small 
a body of water. The morning sun is always 
best, the rays are not so direct and ardent. 
The great mistake in nearly all aquaria is 
that there is too much exposure of the water 
to the action of light, by which the spores of 
minute vegetable organisms contained in the 
water are developed in immense quantities by 
the heat rays of sunlight, till the water as- 
sumes an opaque greenish color, which can be 
overcome only by darkening down the tanks, 
or introducing snails and other animals that 
feed on this vegetable growth. 
This tub was like a pond with its bottom and 
sides — not like the ill-constructed aquaria of 
the present day, with light penetrating the 
water from top, sides and ends, blinding the 
fish and stimulating the plants, till they spin- 
dle away into floating masses of decay. An- 
other advantage about this tub aquarium was, 
that it was constructed of wood — a non-con- 
ductor of heat. The majority of tanks now-a- 
days are constructed of iron and glass, which 
are excellent conductors of heat. 
The conferva are plants of a low order 
known as cryptogams, because they do not 
produce flowers, and their fruit or seed-bear- 
ing organs are not easily discovered. Hence 
the term cryptogam, which literally means 
hidden or secret marriage. The spores are con- 
tained in all water except spring water, and 
are also frequently present in the atmosphere. 
It is slow of growth, seldom develops in a well- 
regulated tank till the second year, and re- 
quires from one to two hours' sunlight a day 
and low temperature of water. Goldfish, cray- 
fish, suckers, caddis- worms, snails and some 
varieties of tadpoles will eat up the young 
growth as fast as it develops. None but pure- 
ly carnivorous fish can be placed in the same 
tank without its being destroyed. Dealers do 
not have it on sale, ndr do they cultivate it in 
their tanks, as they prefer plants of freer and 
more robust growth, that can be bunched. 
This tub aquarium ran successfully for sev- 
eral months, till one day I overstocked it with 
animal life and thus unwittingly disturbed the 
balance of nature. The minnows died, the 
green was eaten up by snails, and I concluded 
that I had ofiended the fairies or they had 
moved away, which accounted for the death of 
all and every fish placed in the tub ever after- 
wards. 
In course of time when I had gained a knowl- 
edge of the laws that govern aquaria, I estab- 
lished a more wonderful tub than this one, and 
of this I will tell in some future article. 
A. W. ROBERTS. 
Engraving on Wood. II. 
BY SARAH E. FULLER. 
TN retracing the outline so as to transfer the 
drawing from the paper to the block, the 
point should not bo sharp enough to cut the 
tracing paper. Retrace carefully every line, and 
do not bear too hard or you will bruise the 
wood, but use pressure enough to make the 
marks of the soft pencil come off on the block. 
On removing the tracing paper, a delicate pen- 
cil drawing will be seen, sufficient of the soft 
pencil having adhered to the wood to make a 
distinct drawing. It is now necessary to use a 
hard pencil, the six H being most suitable. 
With this pencil go over every part of the out- 
line on the wood, strengthening the weak lines, 
and correcting any slight irregularities that 
crept in while tracing and re-tracing. Some- 
times a piece of tracing paper, one side of 
which has been rubbed with red lead, is laid 
with the red side next to the block, between 
the block and the tracing. On tracing over 
this, the delicate drawing made on the wood 
will be red, and then can be drawn over in the 
same manner as the lead pencil tracing. This 
method is convenient when there are many 
lines, and they are close together. 
When the outline is completed, and it is de- 
sired to put in the shading, this may be done 
with the pencil if the shades are light, and 
made up of lines crossing each other, making 
what we technically call "fac-simile" work. 
But if the shades are in "tints," that is, made 
up of even or graduated lines, it is usual to 
" wash" in the tints with India ink — the light 
