80 
POPULAR SCIENCE ISTEWS. 
[April, 1891. 
plants, properly acted upon by liglit and under 
other suitable conditions, will, instead of taking 
from, add to the proportion of oxygen present, 
and will thus restore the balance without resorting 
to mechanical aeration. This explains why tanks 
used by early experimenters still exist, their 
tenants living and breeding healthily, and the 
same water as first put in still capable of support- 
ing life. 
A prominent experimenter states that lie placed 
two small gold fish in a glass jar capable of hold- 
ing twelve gallons of water. Half filling the 
vessel with fresh spring water and placing some 
sand and mud at the bottom, with fragments of 
limestone and sandstone, he planted a small Valis- 
neria, a water-plant, in the mud and left the whole 
undisturbed. After a time the water became thick, 
and a coating of scum or confervoid vegetation 
obscured the glass so that the interior could not 
be discerned. On introducing a few water-snails, 
he found that they fed on the conferva as well as 
on the decayed matter of the plant, and soon 
restored the water to a clear and healthy condition. 
The pruning of the older leaves encouraged the 
growth of many small shoots. The snails flour- 
ished on the vegetable matter, which they con- 
sumed, and the fishes thrived on the eggs which 
the snails deposited, and in the renovated water. 
The aquarium is subject to a great many modi- 
fications in shape. The proper proportion of 
dimensions should be something like this : Length, 
twenty-four inches, width, eighteen inclies, and 
depth, ten or twelve inches. . A great many, and 
in fact the greater number, are of improper form, 
being as deep or deeper than they are wide. In 
an aquarium the fact that the proportional surface 
to the air is of far more importance than the 
volume of water contained, should be borne in 
mind. A sloping bottom is also preferable. The 
bottom should be laid with sand or small gravel 
suited to the condition they are intended to 
represent. Some water animals like to burrow, 
and should therefore have a bed of sand in which 
to gratify their desires in that direction. A few 
bright pebbles added give the vessel a pleasing 
appearance and afford shejter for minute animals. 
A few larger stones laid on the gravel is all that is 
necessary to give shelter to fish. Ornamentation 
in this case should consist in the water-plants. 
Clear, river water is preferable, as it is best for 
both animal and vegetable life. Among the plants 
common and easy to get for your aquarium are, 
"starworth," "water soldier," "new water weed," 
"frog bit," and "water plantain." Most of the 
smaller species of fish will live and breed freely in 
tanks well supplied with oxygen, and there is no 
way in which the beauties of their forms and 
markings can be so well seen as through perpen- 
dicular, evenly moulded glass. Here their graceful, 
easy movements can be watched without their 
being distorted by refraction. Most of them enjoy 
their dwelling, if we can judge from their lively 
yet not restless bearing. It must be remembered 
that they are mostly animal feeders, and if put 
into a vessel with other animals smaller or weaker 
than themselves, they will not live quite as happily 
as the cat and mice in the "happy family." Some 
fishes are much more voracious than others. I 
heard of an instance where a pike two inches long 
attacked and destroyed a fish of another species 
half as long again. 
Among the many suitable fish for aquarium 
study, the gunflsh, perch, catfish, young bass, 
trout and German carp are preferable where they 
are obtainable. Water tortoises and newts if kept 
should be supplied with mud and also some exposed 
rock where they can stay out of the water at their 
leisure. Among molluscs, fresh water mussels, 
snails, and slugs are useful as scavengers. The first 
few days your aquarium should be well watched 
for dead fish. It is natural that some fish so 
recently introduced into strange surroundings 
will die, and it is very necessary that these bodies 
should be removed before putresence takes place, 
as the water will become putrefied to the danger 
of the living occupants. If a green turbidity 
arises on the water, it can be easily remedied by 
excluding light from the aquarium for a few days. 
For the purpose of occasional aeration a drip-glass 
may be arranged by means of which a portion of 
the water may be lifted and allowed to drip slowly 
back. There is no better or more interesting way 
of gaining a knowledge of nature than by a close 
and careful attention to a well-stocked aquarium. 
[London Chemical News.] 
GENESIS OF THE ELEMENTS. 
BY BR. WILLIAM CROOKES. 
It is now generally acknowledged that there are 
several ranks in the elemental hierarchy, and that 
besides the well-defined groups of chemical ele- 
ments, there are underlying sub-groups. To these 
sub-groups has been given the name of meta-ele- 
ments. The original genesis of atoms assumes 
the action of two forms of energy working in time 
and space — one operating uniformly in accordance 
with a continuous fall of temperature, and the 
other having periodic cycles of ebb and swell, and 
intimately connected with the energy of electricity. 
The centre of this creative force in its journey 
through space scattered seeds or sub-atoms that 
ultimately coalesced into the groupings known as 
chemical elements. At this genetic stage the new- 
born particles vibrating in all directions and with 
all velocities, the faster moving ones would still 
overtake the laggards, the slower would obstruct 
the quicker, and we should have groups formed in 
different parts of space. The constituents of each 
group whose form of energy governing atomic 
weight was not in accord with the mean rate of 
the bulk of the components of that group, would 
work to the outside and be thrown off to find other 
groups with which they were more in harmony. 
In time a condition of stability would be estab- 
lished, and we should have our present series of 
chemical elements each with a definite atomic 
weight — definite on account of its being the 
average weight of an enormous number of sub- 
atoms or raeta-elements, each very near to the 
mean. The atomic weight of mercury, for instance, 
is called 200, but the atom of mercury, as we 
know it, is assumed to be made up of an enormous 
number of sub-atoms, each of which may vary 
slightly round the mean number 200 as a centre. 
We are sometimes asked why, if the elements 
have been evolved, we never see one of them trans- 
formed, or in process of transformation, into 
another? The question is as futile as the cavil 
that in the organic world we never see a horse 
metamorphosed into a cow. Before copper, e. g., 
can be transmuted into gold it would have to be 
carried back to a simpler and more primitive state 
of matter, and then, so to speak, shunted on to 
the track which leads to gold. 
This atomic scheme postulates a to and fro 
motion of a form of energy governing the electrical 
state of the atom. It is found that those elements 
generated as they approach the central position 
are electro-positive, and those on the retreat from 
this position are electro-negative. Moreover, the 
degree of positiveness or negativeness depends on 
the distance of the element from the central line ; 
hence calling the atom iu the mean position elec- 
trically neutral, those sub-atoms which are on one 
side of the mean will be charged with positive 
electricity, and those on the other side of the mean 
position will be charged with negative electricity, 
the whole atom being neutral. 
This is not a mere hypothesis, but«iay take the 
rank of a theory. It has been experimentally 
verified as far as possible with so baffling an 
enigma. Long-continued research in the labor- 
atory has shown that in matter whicli has 
responded to every test of an element, there are 
minute shades of difference which have admitted 
of selection and resolution into meta-eiements, 
having exactly the properties required by theory. 
The earth j^ttria, which has been of such value in 
these electrical researches as a test of negatively 
excited atoms, is of no less interest in chemistry, 
having been the first body in which the existence 
of this sub-group of meta-elements was demon- 
strated. 
[Amateur Electrician.] 
ELECTRICAL HEATING. 
Now and again one hears of electric heating in 
a vague kind of way that would hardly lead any- 
body to suppose practical results had been ol)- 
tained. But the fact is that the electrical heating 
apparatus is already in quite general use and that 
several companies have been formed for its intro- 
duction. One of the earlier forms of electric heat- 
ers, which was especially designed for street-car 
use, is not unlike an ordinary radiator, and has 
also been given a shape resembling that of the 
familiar metal foot-warmer. The rapid increase 
in the number of electric street-cars in our north- 
ern latitude has given a stimulus to ingenuity in 
this field, and a new heater has been brought out, 
which, for simplicity and economy of space, seems 
hard to excel. It consists of a narrow strip or 
ribbon of asbestos, inclosed in sheet iron,- about 
three inches in width and one-quarter inch in 
thickness. This strip is placed under the car 
seats, extending from one end of the car to the 
other, and is protected by a wire screen. A 
second strip of the same dimensions is attached 
to the first as a kind of compressing plate, and the 
wires are imbedded in the asbestos. These strips 
are given a zig-zag form, so as to increase the 
length of radiating surface exposed in a given 
area. The current being turned on, the wires, by 
means of the resistance they are purposely made 
to offer to the current, become very hot, and this 
heat is radiated, therefore, steadily and equably 
throughout the car. A more agreeable means of 
heating it would be hard to imagine. No space is 
taken up by the stove, nor are any of the seats 
rendered unpleasant by proximity to the heating 
-apparatus. One part of a car is just as warm as 
the other, and by means of various methods of 
arranging the strips the degree of heat can be 
regulated to a nicety. There is no need to get 
the car ready for the approach of winter nor to 
make any special arrangement whatever, other 
than the simple attachment of the strips under 
the seats. All that is necessary when heat is 
wanted is that either the driver of the electric car 
or the conductor shall switch or turn on the cur- 
rent through the heating apparatus, and thus the 
same agency which propels the car and lights it 
also provides it with waimth. The question 
which comes into one's mind on riding in one of 
the many electric cars now equipped in this ex- 
cellent manner is why something of the saine 
kind cannot be rendered available for oflice or 
household use. The probability is that it soon 
will be. In speaking of electric car heating at a 
recent street railway meeting at Columbus, O., 
