"Oxygen is a principle existing in the air, of which it forms the respirable part, and which is also necessary to combustion. Oxygen, by combining with bodies, makes them acid, whence its name, signifying generator of acids."-Todd's Johnson.

Hydrogen is water-producer. Hudor (udwp), in its form hydro, is found also in hydrocephalous (Greek, kepaλn, keph'-a-le, the head), having water in the head (the brain); and in hydrophobia (Greek poßos, phob-os, fear), water-madness. Hydropsy, water-sickness, is shortened into our dropsy.

"Soft, swollen, and pale, hero lay the hydropsy,
Unwieldly man, with belly monstrous round."

Thomson, "Castle of Indolence." Hydrography is properly the opposite of geography; for as the latter, considered in its component parts, is a description of the land, so the former is a description of the water. By usage these significations are modified, so that geography, signifying a description of the surface of the earth, comprises hydrography, which describes, by maps, charts, etc., the surface of the water, and especially the sea-coast, with its rocks, islands, shoals, and shallows.

Christopher Columbus, the first great discoverer of America, was

a man that earned his living by making and selling hydrographical

maps."-Chambers.

By derivation, grammar is the science of letters. This is not an incorrect definition, for the science of letters, considered in all its relations, is the science of language, of which letters are the elementary portions. "Letters" is often used, however, for systematic knowledge, or the results of a high and varied education. So we speak of "a man of letters." In this sense the term is used in the question, "How knoweth this man letters, having never learned ?" (John vii. 15.) The hostile questioner took Jesus to be ignorant (Acts iv. 13)—that is, as in the original, idtwτns (id-i-o'-tees), idiot, untaught-such as Peter and John were accounted.

"I made it both in forme and matter to emulate the kind of poeme which was called epithalamium, and by the ancients used to be sung when the bride was led into her chamber."-Ben Jonson, "Masques.” Greek Words. Stems. English Words. hagio hagiography.

Pronunciation. hag'-i-os hek'-a-ton

Meanings. holy hundred

'Αγιος

Εκατον

Ήλιος

Περι

he'-li-os per'-i

helion

peri

Απο

ap'-o

from

ар

Ημερα

he'-mer-a

a day

hemer

ephemeral.

Επτα

hep'-ta

hecatombs of most happy desires, praying all things may prove prosperous unto you."-Drummond. «

Isothermal lines are lines of equal heat in different parts of the globe. Iso is also found in isosceles (σkeλos, skel'-os, a leg), applied to a triangle which has its two sides of the same length. most distant from the sun; perihelion is that point in which it Aphelion is that point of the orbit of a planet in which it is is nearest to the sun.

Anything whose duration or existence is very short is termed ephemeral, or lasting for a day. Thus, insects that spring into life at sunrise and perish at sunset are styled ephemera,

"There are certain flies that are called ephemera, that live but a day."--Bacon.

account of daily transactions. Ephemerides (the plural of ephe An ephemeris is properly a journal (French, jour, day), an meris) denote a set of astronomical tables, showing the state of the heavens for every day.

The expression homologous is used by Euclid in his " Elements of Geometry," in reference to lines and angles that correspond in relative position, proportion, or structure: hence any two portion, formation, or value, may be said to be homologous. forms or expressions that exactly correspond in position, pro

Comparing the homologous or correspondent members on both sides, we find that the first member of the expression," etc.-Bishop Berkeley, "Analyst."

Apocalypse, by its very derivation, signifies uncovering; in Latin it is unveiling-that is, revelation.

In apocrypha we have another theological term, which is interpreted to mean a hidden writing, from аñо (ap-o), from, and KрUTTE, krup-tine (cryph), to hide. But why should not the apo here have the same meaning as in apocalyse, and so reverse the import of kryptein (English crypt), to hide, and thus signify the disclosed, discovered, or detected writing? Any way, apocryphal is equivalent to spurious, and opposed to canonical or authentic.

"Now, beside the Scriptures, the bookes which they called ecclesiasticall were thought not unworthy sometimes to bee brought into publicke audience; and with that name they intituled the bookes which we term apocryphal."-Hooker, "Ecclesiastical Polity."

Laity denotes the people as contradistinguished from the clergy. In ancient times the laity were ignorant, the clergy learned. Hence arose a broad contrast, exhibiting the people as wicked as well as untaught, and the clergy (clerks) no less holy than instructed. These usages are found in the substance of our language, and still linger amongst us in both thought and feeling.

"He entended (intended) to set forth Luther's heresy, teaching that presthed (priesthood) is no sacrament, but the office of a lay-man or a lay-woman appointed by the people to preache."-Sir T. More. "No wonder though the people grew profane,

When churchmen's lives gave laymen leave to fall."-Drayton. Synthesis is properly the putting together, as analysis (ava, an'-a, up; and Avery, lu'-ein, to undo, to loosen) is the undoing. A watchmaker performs an act of analysis when he takes a watch to pieces, and an act of synthesis when he puts the parts together again.

'Synthesis consists in assuming the causes discovered and established as principles, and by them explaining the phenomena proceeding from them, and proving the explanations."-Newton, "Optics."

66 Analysis consists in making experiments and observations, and in drawing general conclusions from them by induction."—Ibid.

Analysis is the way of discovery, synthesis is the way of teaching or communication. By synthesis men put together and exhibit what they have ascertained by analysis. Metamorphosis denotes a change of form.

"Thus men (my lord) be metamorphosed

From seemly shape to byrds and ougly beasts."-Gascoigne. Metempsychosis (uera, meta, change; ev, en, in; and yuxn, psu'-ke, the soul) has for its Latin equivalent transmigration (trans, over; migro, I change my place).

"The sages of old live again in us, and in opinions there is a metempsychosis. We are our re-aninfated ancestors, and antedate their resurrection."-Glanvill.

Metathesis is a change of position or a transposition. Thus what we write bird was formerly bryd, the i and the r changing

Mythology is the science of fable, and is applied to the religion of the Greeks, the Romans, the Hindoos, etc., in opposition to the pure religion of the Gospel. German philosophy has introduced amongst us the new term myth, as denoting a legend, or a version of facts, shaped and coloured by opinion, fancy, prejudice, by the workings of the intellect, the workings of the imagination, or the workings of the heart. In origin, myth, fable, and legend are one, for the words severally denote a word, something spoken, something narrated. But as old stories soon lose their primitive form, and acquire new shapes and hues, so words pass into legends, and legends are corrupted into fables. Necromancy is the fancied art of learning and disclosing facts by communication with the dead. The witch of Endor dealt necromantically with Samuel at the request of Saul. (1 Sam. xxviii. 7; compare Deut. xviii. 9.)

A pedagogue is a term of Greek origin, equivalent to our schoolmaster. Pedagogue is a word which is now used contemptuously. In an oligarchy the interests of a few predominate. In a democracy the interests of the many prevail. The real and the apparent interests of men are sometimes very different. A polemical spirit is undesirable. Polemical writings are occasionally required. The character of the apostle Paul is very noble. Apostolical virtues are rare. The apostles received their mission immediately from Christ. Without enthusiasm the best of causes cannot be carried forward Enthusiasm is in danger of degenerating into fanaticism.

HYDROSTATICS.-II.

PRESSURE OF LIQUIDS AKISING FROM THEIR WEIGHTCENTRE OF PRESSURE-LEVELS-SPRINGS AND ARTESIAN WELLS.

HAVING now mastered the principle of the equal transmission of pressure in all directions, we must pass on to notice the pressure which is produced by the weight of the liquid itself. Water, in common with all other substances, possesses weight, and this weight must cause pressure on the sides of the vessel containing it. If we have an upright cylindrical vessel with straight sides, and place in it a cylinder just fitting, it will press on the bottom of the vessel with a force equal to its own weight. If now we replace the solid by a liquid having the same weight, the pressure on the bottom of the vessel will remain the same as before, but, in addition to this, every part of the sides of the vessel will sustain an outward pressure. This is clear from the fact that, if we remove the side, or any portion of it, the liquid will no longer retain its shape, but will spread itself out as widely as possible.

E

D

к L

F

The first fact we have to notice about this pressure is that it increases with the depth of the liquid, and in the same proportion, but is * perfectly independent of the shape of the Fig. 4. vessel containing it. In the proof of this and other propositions, we shall make the following assumption that any portion of a bulk of fluid may be supposed to become solid without making any difference in the state of equilibrium of the liquid, or in the forces which act upon it. A moment's thought makes this fact self-evident. Let ABCD (Fig. 4) represent a vessel filled with water to the level A B. Take in it any horizontal layer, EF, and in this let a portion, & H, having an area of 1 square inch, be supposed to become solid. It is now kept at rest by two equal

and opposite forces-the weight of the water above it, and the upward pressure of that below it. Now the former is clearly equal to the weight of a column of water having, like G H, an If area of 1 square inch, and whose height is equal to G K. & H be now sunk to a lower level, it will have to sustain the weight of a longer column, and therefore the pressure of the water on it will be greater. We see thus, that the pressure increases with the depth. If we take a number of bags of flour or sugar, and pile them one on the top of the other, the lower ones have to sustain the weight of those above, and will accordingly be compressed to a greater extent than those which are higher up in the pile, and therefore have to sustain the weight of fewer. P Just in this way each layer of liquid has to sustain the weight of all above it, and thus the lower layers are more powerfully compressed. An illustration of the great pressure thus exerted is seen in the fact that if a tightly-corked bottle be sunk to a depth in the sea it will be broken, or else the cork will be driven into it.

Fig. 5.

We have now to show that this pressure is quite independent of the shape of the vessel. Instead of that shown in Fig. 4, let us have one made in the shape of a small tube fitted into the top of a larger one, as shown in section in Fig. 5. The pressure on the part directly under H E will, as before, depend on the height of the column of water above it. But every part of the base, M N, must sustain the same pressure, for otherwise there would not be equilibrium, but the liquid would move towards that part where the pressure was least. Every part of a horizontal layer sustains then exactly the same pres sure. We thus arrive at the apparently strange result, that if the vessels represented in Figs. 4 and 5 be filled to the same height, and the areas of their bases be equal, the pressure on each base will be the same, although one contains a much larger quantity of water than the other. We must not, however, suppose that, since the pressures are equal, the vessels, if placed in opposite pans of a pair of scales, would balance each other.

This paradox is easily explained. Suppose we have a box, the lid of which fastens down by a catch, and we place a spiral spring inside, so that when the lid is closed the spring is powerfully compressed, the pressure on the bottom is manifestly much greater when the box is closed than when it is open, and yet it weighs no more. The fact is, the spring presses the top of the box upwards with exactly the same force as it presses the bottom downwards, and these two forces neutralise each other. So in the vessel shown in Fig. 5, the pressure of the liquid, being transmitted in all directions, presses up against the surface PGFR, and balances a part of the pressure on the base, and the pressure on the scale pan will be the difference between these two, the upward pressure on PR being exactly

1 h t

Fig. 6.

equal to the weight of the ring of water required to make up the quantity there is in the other vessel.

The following experiment affords a proof of this principle of the pressure being dependent alone on the area of the surface and the depth of liquid. Procure three vessels of the shapes represented in Fig. 6, and let their bases be made of exactly the same size, and arranged so as to open like trap-doors by means of hinges.

To a similar part of the base of each attach a string, and let these pass over pulleys and have equal weights affixed to their ends, so as to keep the bottoms closed.

If now water be poured into each vessel it will be found that the bottoms will open, not, as might be supposed, when an equal weight of water has been poured in, but when the water stands at the same level in each.

We see thus, that when filled to the same height the bases sustain exactly the same pressure, and this pressure is equal to the weight of the fluid in the middle vessel.

Having thus seen that pressure is proportional to the depth, we can examine the variations in it at the different parts of the sides of any vessel or of an embankment. If we have a column of water having a base 1 square inch in area, the pressure on a layer of it at a depth of 1 inch will be equal to the weight of a cubic inch of water, or 252.5 grains; and at a depth of 2 inches the pressure will be equal to the weight of 2 cubic inches, and so on, varying in direct proportion to the depth. We see thus, that an embankment or sea-wall should also increase in thickness in the same proportion. The pressure against such an embankment is, it may be observed, quite independent of the extent of the body of water it sustains. The same strength is required to resist the pressure on the side of a narrow mill-stream as in a sea-wall, provided the depth be the same in each case.

If we divide the side of a rectangular vessel into any number of equal divisions, the pressures at these divisions will be in the proportion of the consecutive numbers 1, 2, 3, etc.

Let these divisions be one foot apart. Then at the first, the pressure on any portion will be equal to the weight of a column of water one foot high. The pressure on a square foot at this depth will therefore be equal to the weight of a cubic foot of water. We must not, however, suppose that this will be the pressure on a square foot of the side extending from the surface to the first division, for at the surface the pressure is nothing, and it gradually increases with the depth. The mean pressure on the square foot is therefore equal to that at a depth of 6 inches, and the total pressure is equal to the weight of a column of water of this height. So if we want to know the pressure on the rectangular side of a vessel, we must ascertain its area, and multiply this by half the depth; we shall thus find the number of cubic feet of water to which the pressure is equal. An example will make this clear. Suppose we have a vessel 5 feet long and 4 broad, and it be filled with water to a depth of 4 feet, what is the pressure on the four sides, and what on the bottom? We will take the sides first; each of these is 5 feet by 4, and has therefore an area of 20 square feet; each of the ends has also an area of 4 feet by 4, or 16 square feet. The total area of the two sides and the two ends is therefore 40 + 32, or 72 square feet. Now the depth of the water being 4 feet, the mean pressure is found at a depth of 2 feet, and thus the total pressure on the sides is equal to a column of water 72 feet in area and 2 feet in height; that is, to the weight of 144 cubic feet of water.

In these calculations we must remember the following weights:

A cubic foot of water weighs about 1,000 ounces, or 62} pounds.
A cubic yard weights of a ton.

A cubic fathom weighs 6 tons.

The total pressure on the sides is therefore 144 x 629,000 pounds, or rather over 4 tons. The pressure on the bottom is 5 x 4 x 4, or 80 cubic feet of water. This is equal to 80 x 624 or 5,000 pounds, which is nearly 24 tons.

Sometimes the surface on which we want to ascertain the pressure is not a rectangle, but we may always take the mean depth as that of the centre of gravity of the surface, and, multiplying this by the area, we obtain, as before, the pressure. We thus see that when water has to be confined by a wall or embankment, the safest plan is to spread it out as widely as possible so as to diminish the depth, and also to let the edges gradually slope.down to the middle. If the depth against the embankment be great and a small leak occur as it may, from the hole of a rat or some similar cause-the water, when once it has found a way, soon wears a larger hole, and the upward pressure of the water is often so great as to blow up the bank. It is on account of the great pressure thus produced by a body of water that lock-gates have to be made so strong; and to enable them to stand better, they are usually made so that when closed they are in the form of an arch, the convex side being turned in the direction in which the water is highest. When the gates are large, a sliding panel, worked by a screw, is introduced near the bottom, and through this opening the water flows till it stands at the same level on each side. With out this the pressure would be too great to allow of the gates being opened.

AL

Fig. 7.

B

Now, although the mean pressure is that at the centre of gravity, we must not imagine that this point is the centre of pressure-that is, that a support placed behind this would balance the pressure. If we suppose the surface divided into layers, there will, if it be rectangular, be as many layers above the centre of gravity as below it; but, since the pressure is greater on the lower layers than on those higher up, the larger part of the pressure will be below the centre of gravity. The centre of pressure is therefore below this point. Its position varies with the shape of the surface, but in a rectangular surface is situate at about two-thirds of the depth. This fact should be borne in mind in the construction of lock-gates, for if a hinge be placed near the top, and a pivot and socket at the bottom, an undue pressure is thrown on the lower support, and thus there is a tendency to wring or twist the gates. The supports should be arranged as nearly as possible equi-distant from the centre of pressure, one being near the bottom, and the other about a third of the way from the top, as then the pressure is equally distributed.

There is another property of liquids which results from the facts already noticed, and that is, that the surface always maintains its level and forms an horizontal plane. This fact is familiar to us by every-day experience, and the reason of it is easily seen. Let A B C D (Fig. 7) be a vessel containing liquid, and let the surface be supposed to have the figure A G H B. Take any layer, E F, in the fluid, and imagining it to become solid, let us see what is the pressure at each end of it. At E it is equal to that of a column of water having the height GE; at F it is equal only to the column F H. The former of these is obviously greater, and therefore equilibrium cannot exist till this difference is removed. The particles of fluid will therefore move from E towards F until the surface becomes even.

Fig. 8.

N

Exactly the same result will occur if, instead of one vessel, we have any number communicating with each other, no matter what their shape may be. The apparatus usually used for the proof of this is shown in Fig. 8. A number of glass vessels, varying greatly in size and shape, but all having the same height, are arranged so as to communicate freely with each other. If now water be poured into any one of them, all will be filled, and the water will rise in each of them to the same height; or, if a stopcock be fitted at the bottom of each, and they be filled to different levels, immediately on the taps being turned, the level will become the same in all. The mass of water in м is many times greater than in N, yet it will stand at exactly the same height in each.

Familiar illustrations are seen in tea-pots, or other vessels used to pour liquids from. The spout is always so arranged that the open end of it is at least as high as the surface of the liquid within.

Fig. 9.

The practical applications of this principle are numerous and important. The most common is the level, which is such an important instrument in surveying operations. In making roads or railways, or still more in canals, it is necessary that all parts should have as nearly as possible the same elevation, so as to avoid inclines. It is desirable, too, to do this with as little labour as possible, and therefore that route is chosen which will require least cutting or embankment. To ascertain this, levelling is required. The form of level which shows best the

principle, though not the one commonly used, is shown in Fig. 9. A glass tube is taken, and each end is bent at right angles. This is supported on a stand, and water poured in so as to rise a little way in each limb. A float rests on the liquid at each end, supporting a framework with cross wires. A graduated pole is then set up at a distance, and the observer notes what part of it is in a straight line with the points where the wires cross, and thus finds the difference in height between the place where the pole is and that where he stands.

The surface of the earth, however, is not a true level, but a curve which differs from a straight line by about eight inches in a mile; an allowance to this extent has accordingly to be made, for the surface of water keeps to the curve, or natural level, as it is called. In a small surface this is not noticed at all, but we observe that when a ship is going out to sea the hull is hidden by this curve, while the masts still remain visible.

The more common form of level consists of an even tube of glass nearly filled with spirit, so that only a small bubble of air remains in it. Both ends are then closed up, and it is mounted in a case, so that the sides of the tube are exactly parallel to the bottom. If it be placed on an horizontal surface, the bubble will remain exactly in the middle; but if either end be elevated at all, the bubble will rise to that end. In levelling, one of these levels is fixed to the stand of the telescope so as to be parallel to it. It is then adjusted by means of thumbscrews so as to be perfectly horizontal, and on looking through the telescope the elevation on the pole may be read off with much more accuracy and at a greater distance than when the other form of level is used.

It is on this principle of water always finding its level that a town is supplied with water. If there be a convenient elevation outside the town a reservoir is made there, and the water pumped up into it. Pipes are then laid on from this to all parts of the town, and in these the water will rise to an eleva tion nearly equal to that of the reservoir. The small difference in height arises from the friction of the water in the pipes. Instead of a reservoir the water is sometimes forced into a lofty pipe open at the upper end, and from this it flows to all parts, the principle being exactly the same. In the same way a fountain acts, and any one with a little mechanical ingenuity can easily fit one up for himself. A reservoir has to be provided at a height exceeding that to which the water is required to rise, and á pipe is brought down from this to the jet. Springs and artesian wells depend on this same principle. In mountainous and elevated districts there is always a larger fall of rain, because the hills condense the clouds. This rain soaks in through crevices of the rocks, till it finds its way to some large cavity. Many different crevices often lead thus to one large chamber, and the water being unable to find any other escape, rises from this to the surface, forming a spring.

In some places all the upper strata of the soil are easily permeated by the rain, but at a greater depth there exists one through which it cannot pass. It accordingly accumulates there, and if a hole be bored in the ground down to this level, the water will frequently rise to the surface and form an artesian well. One of these near Paris is bored to a depth of 1,800 feet, and the water in it rises with such force that in a vertical tube it would rise over 100 feet. It is said to be capable of supplying over 14,000,000 gallons per day.

EXAMPLES.

ESSAYS ON LIFE AND DUTY.—XI.
ECONOMY.

PERHAPS there is no word in the English language that has been so foolishly narrowed in its meaning as the word Economy. Most people think of it as a saving of money, as though to be economical was, in a certain sense, to be stingy or mean. Now economy in its true interpretation is the art of management-is the wise adaptation by which we arrange time, health, and strength so as to produce the best results. It is human labour and opportunity wisely and well applied: not a mere saving or hoarding, but rather a wise investment and expenditure of what we have. The young man who saves the same amount of money which his friend, who has equivalent means, spends in attending a French or German class, or in learning the rudiments of science, is in no sense economical. The day will come when that knowledge of French or German will be of far more value to him than all the money he saved up by not paying for the learning of these languages. He will lose a higher appointment, into which his more cultured friend will step, and will be obliged to drone on in the position he at first occupied, because he is not fitted for a better. Time and opportunity are now gone for ever, and were wasted whilst he saved his little hoard of silver or of gold.

Economy requires thought. We have to discern not only what to do, but the very best way of doing it; and this, too, in every branch of life. Think of the positive waste that is continually going on-not through God's arrangements, for they are so perfect that there is not the smallest waste in all creationbut through man's short-sighted ignorance or wicked sloth! The late Lord Palmerston once cleverly remarked that DIRT was only "matter in the wrong place:" a saying as true as it is terse, for there is sure to be a need for everything, and a place for everything, in the wide universe of God.

Young women ought to be early educated in the economy of a wise management, for such men as Soyer have clearly shown us that the most nutritious and delicate parts of fish, flesh, and fowl are positively cast aside and despised; whilst in some households, to be liberal means to be wickedly wasteful and carelessly prodigal. Plentifulness is best ensured by a clever economy, and not only that, but quality is procured by it as well as quantity.

Young men should be taught to be economical. Who does not know two such in positions where their means are about equal, where, on the one hand, there are music, books, and nameless elegances, with a little in hand beside; whilst in the other case there is an insufficiency even of clothes and comforts, and a constant "miserabile" in the manner, as though it were a hard lot indeed ?

Time-spare time-economically used produces wonders. Those who could only attend evening classes have by their appreciation of advantages within reach distanced in the race others who have had the whole day for mental toil. Who has not known some who, with only a few pounds for their summer holiday, have managed to see the cathedral of Milan, and enjoyed much of the pleasure of a Continental tour? Careful management must, of course, form part of most persons' lives. We are not born into positions where we can gain the good we would obtain -apart from sweat of brain-nor would it be well for us that we should. Wise persons have to weigh and ponder matters, and turn them round and round in their minds, as ladies turn material in their hands to see how it will best cut out two garments instead of one. Sometimes, indeed, the expression is

20 tons?

2. What is the pressure on the sides and what on the bottom of a vessel 10 feet by 6, filled with water to a depth of 4 feet 6 inches ?

3. A canal is 9 feet wide, and the water rises against a lock-gate to the height of 12 feet 6 inches. Required the pressure on the gate. 4. Two pistons are fitted into a vessel. One has an area of 4 square inches, the other is 7 inches in diameter. What force must be exerted on the small one to produce a pressure of 330 pounds on the other? (The area of a circle is 34th times the square of the radius.)

5. A canal is 5 feet deep, but the bank slopes so that the length of it from the surface to the bottom is 6 feet. What pressure does a portion of the bank 12 yards long sustain ?

6. The pressure on a surface 3 inches long and 2 inches wide, immersed in a vessel of water, is 3 pounds. If it be sunk 3 feet deeper, what will the pressure be?

means, for the most part, "I dislike bother, and trouble, and thought." Let alone management altogether, and see what most households and what most lives would come to. Those who dislike economy are in the end as cruel as they are careless: other people have to discharge obligations they have incurred and to think for them because they have not liked the worry of thinking for themselves.

Economy applies to health as well as to other things. It is not wise to exhaust the brain force, but to use it with conside ration and care. A may do almost double the work of B in one given year; but then all the next year A may be knocked up and nervous, and unable to work at all. Surely there must be great want of economy in that. Here judgment and conscience must step in, that we may be led to do not only what we can, but

what we ought. You may overwork yourself for months without feeling it much, but you will one day pay the penalty; draw a bill upon your constitution if you like, but it is sure to come due in time, and a heavy pay-day it will be.

There are many aspects of economy: there is the political economy of the nation, the social economy of home, and the personal economy of life. It is of course pretty certain that in each of them there will be differences of opinion as to method, but as to the wisdom of economy in itself no thoughtful people will be at issue for a moment; and economy in relation to personal life will to a great extent be regulated by taste and feeling. It would be foolish for one who had no ear for music to spend years in the hard toil of trying to play well on an instrument, and for one who had no eye for distance to learn perspective. We must be judges to a great extent of our own powers, and a true economy consists in physically, mentally, and morally making the best of ourselves.

As political economy advances, and men become interested in it, we may hope for the day when it will be the aim of society to bring as easily as can be within the reach of the multitude good

art, good scientific appliances, and good things of every kind, so that these may not become the prerogative and appanage only of the rich or great, but may be made available by all. And concerning personal economy, let that be no selfish or epicurean thing, but an economy which embraces home, children, employers, servants, and secures for all as much as may be gained of health and joy, wisdom and wealth. Many may be found who blame everybody but themselves for their failures in life, whereas it often happens that the said complainants commenced life easily and even luxuriously, whilst others had to exercise some little self-denial and care; or, perhaps, they wasted precious opportunities for advancement and improvement which never recurred again.

It may sound strange to some, that economy is not so much saving as spending; but it is the making careful and clever use of the faculties within us and the opportunities without us. In the science of life and duty perseverance and energy often come to untimely ends, because they are not united in fellowship with

a wise economy.

LESSONS IN CHEMISTRY.-XIII. COMPOUNDS OF CARBON WITH NITROGEN AND SULPHUR

THE HALOGENS-CHLORINE.

CARBON forms other compounds than those with oxygen and hydrogen already described. It enters into combination with chlorine, but the four products will not require attention until we reach organic chemistry. Only one compound is known with nitrogen. It is

Cyanogen (symbol, CN; combining weight, 26; and the density has been found to be 26, and therefore its true symbol is C2N2). -It was discovered in 1814 by Gay Lussac, and derives its name, "a producer of blue," from the fact that it is the chief agent in the production of Prussian blue. When bodies which contain carbon, nitrogen, and potash are heated together, a remarkable salt, the cyanide of potassium (KCN), is formed, which is characterised by crystallising in large yellow tables. To produce this, substances rich in nitrogen-such as hoofs, hide-clippings, woollen rags, dried blood, etc.-are heated in an iron pot with two and a-half times their weight of potassium carbonate. The resulting potassium cyanide is now dissolved out by water and allowed to crystallise. It is commonly called the prussiate of potash. When iron, or any of the proto-salts of iron, is added to a solution of this prussiate of potash, large four-sided tables are deposited, which are ferrocyanide of potassium. When ten parts of this salt are dissolved in four times their weight of warm water, and distilled with seven parts of sulphuric acid diluted with twice its weight of water, the first portion of the liquid which comes over is a dilute solution of hydrocyanic or prussic acid (HCN). Mercuric cyanide may be made from this by saturating the solution with red oxide of mercury, and then evaporating. If this salt be heated, it is decomposed into cyanogen and mereury; and thus it is we get the compound. It is found to be a transparent, colourless gas, poisonous and inflammable; its flame is edged with purple; being soluble in water, it must be collected over mercury. If the gas be passed through iron tubes at a high temperature, it is decomposed, charcoal is deposited, and, as might be

When a solution of ferrocyanide of potassium is added to a solution of a sesquisalt of iron, the well-known Prussian blue is precipitated. Hydrocyanic acid (HCN) has been alluded to, and the first stage of its preparation given. If it be required in its pure state, dry calcium chloride is added to the above solution, and This must never be attempted save by the liquid distilled. is the most powerful poison known. experienced persons, and only then for some good reason. It liquid, which gives off vapour, a breath of which would be fatal. It is a limpid, colourless and in cases where death has not resulted, the treatment is to The poison seems to attack and prostrate the nerval system, pour cold water down the spine.

leaves of many plants it is found in minute quantities.

The acid has the odour of almonds, for in the kernels and

oxygen enters, but they become too complicated for an elementary study of chemistry.

There are other compounds of carbon and nitrogen into which

density, 38).-A porcelain tube is passed through a charcoal Bisulphide of Carbon (symbol, CS2; combining weight, 76; occasionally, into its upper end, pieces of sulphur are thrown, furnace in an inclined position; it is packed with charceal; and then the tube is stopped up by a cork. The sulphur is vaporised, and combines with the carbon, forming the bisulphide of carbon. A glass tube attached to the lower end of the porcelain tube conducts the vapour into a condenser, which high refractive power, and possessing a fetid odour. It dissolves is kept cool. Here there collects a mobile liquid of a very fire," for when a bottle of it breaks, the bisulphide rapidly sulphur and phosphorus. evaporates, dopositing the phosphorus in so finely divided a state, that it soon spontaneously ignites. It also acts as a solvent on gums and india-rubber.

This latter solution is the "Fenian

THE HALOGENS.

There are four elements which closely resemble each other, and which, from the fact that they combine directly with the metals to form salts, have received the name of halogens, "saltproducers." These elements are chlorine, bromine, iodine, and fluorine.

CHLORINE (symbol, Cl; combining weight and density, 35.5). --Chlorine is the most prominent member of the group. It is very widely disseminated through Nature, in combination with sodium, with which metal it forms common salt (NaCl).

Preparation. There are two ways by which this gas may be obtained :

1. Dilute sulphuric acid with its own bulk of water; allow it to cool, then to fourteen parts of this in a Florence flask add four parts of common salt, intimately mixed with three parts of black oxide of manganese. This reaction will ensue— 2H,SO.+2NaCl + MnO, Na,SO, + MnSO, + 2H,O + 2C1. 2. If hydrochloric acid be added to black oxide of manganese, the effect will be the liberation of chlorine, thus—

MnO, + 4HCI = MnCl, + 2H,O + 2C1.

The gas is greenish yellow, hence its name, and is about two and a-half times heavier than air. When submitted to a pressure of four atmospheres, it becomes a liquid, which as yet has never been frozen. The gas is best collected in the usual way, but the water must be warm, for cold water absorbs twice its bulk of the gas. Such a solution is a very convenient way of keeping chlorine for test purposes. The bottle may be labelled "Chlorine water," and kept well stoppered and in the dark, for light causes the chlorine and the hydrogen of the water to combine. On account of its weight, the gas may also be collected by "displacement," by passing the delivery tube to the bottom of the jar.

It will be found to possess a most irritating odour, and if breathed in any quantity may produce ulceration of the lungs. Since it does not combine directly with oxygen, chlorine is not combustible; but its most distinctive property is its great affinity for hydrogen. If, therefore, a taper be introduced into a jar of the gas, it will burn with a smoky flame. The combustion is due to the combining of tho chlorine