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 elevation 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 a 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.

1. In an hydraulic press the diameter of the small piston is threequarters of an inch, and that of the large one 9 inches. The lever is 2 feet long, and the piston is attached 4 inches from the end. What

power must I apply to compress any substance with a force of

20 tons?

ESSAYS ON LIFE AND DUTY.-XI.

ECONOMY.

Now

FERHAPS 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. 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 expen. diture 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, is 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 DIET 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 bo 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 heard, "How I dislike managing kind of people!" but this 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.

it from the surface to the bottom is 6 feet.

portion of the bank 12 yards long sustain ?

What pressure does a

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?

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 appanago 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). Mercurio 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 mercury; 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. stage of its preparation given. If it be required in its pure Hydrocyanic acid (HCN) has been alluded to, and the first state, dry calcium chloride is added to the above solution, and experienced persons, and only then for some good reason. the liquid distilled. This must never be attempted save by It liquid, which gives off vapour, a breath of which would be fatal. is the most powerful poison known. 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

There are other compounds of carbon and nitrogen into which oxygen enters, but they become too complicated for an elementary study of chemistry.

density, 38).-A porcelain tube is passed through a charcoal Bisulphide of Carbon (symbol, CS,; combining weight, 76; occasionally, into its upper end, pieces of sulphur are thrown, furnace in an inclined position; it is packed with charcoal; 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. fire," for when a bottle of it breaks, the bisulphide rapidly sulphur and phosphorus. This latter solution is the "Fenian evaporates, depositing the phosphorus in so finely divided a state, that it soon spontaneously ignites. It also acts as a solvent on gums and india-rubber.

Here there collects a mobile liquid of a very

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、 + 2H2O + 201. 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 e 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 dir 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 the chlorine

with the hydrogen of the fat, forming hydrochloric acid (HCl). The carbon comes away unburnt as smoke.

Bodies rich in hydrogen will frequently take fire when plunged into a jar of this gas. This is the case with a piece of paper dipped in turpentine. Metals in a finely divided state are violently attacked by the gas. Copper leaf and antimony, which is powdered and slightly warmed, even take fire, the result being in every case a chloride of the metal. The peculiar affinity chlorine possesses for hydrogen gives it the power of bleaching. If grass and fabrics dyed with vegetable colours be dipped into a jar of the gas, they will become white. This will be found to be the case only when the articles are moist; then the chlorine, taking the hydrogen of the water, liberates the oxygen, which, being in its nascent state, is much more active, and attacks the colouring matter, thus bleaching the body. This may be well illustrated by dissolving some indigo in sulphuric acid, and adding to a dilute solution some of the chlorine water above mentioned. The colour entirely disappears. The difference between writing ink and printers' ink is shown by introducing each into a jar of this gas; the former is bleached.

This property of chlorine makes it valuable as a disinfecting agent. It attacks the hydrogen of the noxious gas, and thus destroys it.

Hydrochloric Acid (symbol, HC1; combining weight, 36-5; density, 18-25). This liquid is also called muriatic acid, or spirits of salt; it is water largely impregnated with the gas hydrochloric acid, which is prepared by gently heating common salt and sulphuric acid in a flask :

NaCl + H2SO1 = HCl + NaHSO.. The gas which comes off is colourless, 1-27 times heavier than the air, and possesses a pungent odour. In contact with the air it combines with moisture, giving rise to white fumes. At a pressure of 40 atmospheres it becomes a clear liquid. Its composition may be determined both synthetically and analytically by the eudiometer. If equal volumes of chlorine and hydrogen be introduced into the instrument, on the passing of the spark they combine, forming HCl. There is no diminution of volume. Thus

HCl = HCI

1 + 1 = 2.

If now a series of electric sparks be passed, some of the gas is again decomposed, and the unaltered acid may be removed by allowing a few drops of water to rise up through the mercury; these absorb the undecomposed HCl. The remaining gas is found to be equal volumes of H and Cl. These gases, when mixed in equal proportion, will combine, with an explosion, in sunlight.

Large quantities of this acid are made as a bye product in the manufacture of sodium carbonate. In this, its commercial state, it is very impure, since it contains iron in the form of a chloride, to which its yellow colour is due, and also sulphuric

acid and arsenic.

The result of the action of hydrochloric acid on metals is that chlorides of the metals are formed. Their various salts

may be found by replacing the H in the HCl, according to the atomicity of the metal. The presence of a chloride in a solution may be at once detected by a few drops of silver nitrate. The white, curdy silver chloride falls.

Aqua regia is a mixture of nitric and hydrochloric acids, which is capable of dissolving both gold and platinum. Oxides of Chlorine.-Although these elements do not combine by direct means, yet in indirect ways five compounds have been produced:

Hypochlorous acid HCIO Chlorous acid HCIO, Peroxide of chlorine. C1,0.

Chloric acid Perchloric acid

HCIO, HCIO..

Hypochlorous Acid (HCIO).-The prefix "hypo" is from the Greek ro, under, or beneath, signifying that this acid has less oxygen in it than chlorous acid. It may be obtained by shaking up mercuric oxide with chlorine water. The reaction is

It is chiefly noted as a powerful bleacher, being the active principle in bleaching powder, which is a mixture of calcium chlorite (CaCl,) and hypochlorite (CaCl,O,), and is made by allowing chlorine to enter the top of a chamber in which are trays of well-slaked lime one above the other. The gas falls by its weight, and is absorbed by the lime.

Chloride of lime, as this compound is usually called, emits the odour of hypochlorous acid. When exposed to the air, carbonic acid gradually displaces the chlorine which is given off. This makes this substance a valuable disinfectant, as the quantity of the gas emitted is so small as not to be injurious, and yet effective. The best mode of using it is to dip cloths in a solution of the powder, and hang them up.

Chloride of lime is used as the great bleacher. The calico, etc., is boiled in lime-water and a weak solution of caustic soda, to remove the grease of the manufacture and the "dressing." It is then soaked in a solution of two and a-half per cent. of bleaching powder in water. But the action is not discernible until the fabric is "soured" or dipped in a weak solution of sulphuric acid and water. Thus the chlorine is liberated in the fibre of the cloth, and the bleaching is effected. Sometimes this process is repeated, and finally the articles are thoroughly washed in water to remove all traces of the acid. Chlorous Acid (Cl,O,).-To prepare this gas, three parts of arsenious acid, and four of potassium chlorate, are made into a paste with water; sixteen parts of pure nitric acid (specific gravity, 1-24) are added; the whole is placed in a small flask, which is filled up to the neck with the mixture, and a very gentle heat applied by means of a water-bath.

collected in dry bottles by displacement. The The yellow-green gas may be greatest care is required in its manipulation, Cent., and also if it come into contact with as it explodes at a temperature of about 56° any very combustible body. Its formation is due to the deoxidisation of the chloric acid in the potassium chlorate.

Fig. 43.

Peroxide of chlorine (Cl,O) is a gas which explodes as soon as it touches organic or combustible bodies. It is prepared by pouring equal parts of sugar and potassium chlorate, sulphuric acid on potassium chlorate. Mix each in powder; then pour upon them a few drops of sulphuric acid; the whole will ignite. On this principle the first attempt at matches was founded.

bottom of a tall glass full of water (Fig. 43), also add a few Place a piece of phosphorus about the size of a pea at the sulphuric acid to the bottom of the glass. The phosphorus enters grains of potassium chlorate; through a long tube pour a little into combustion with the peroxide of chlorine as it escapes.

of chlorine gas be passed through a strong solution of caustic Chloric Acid (HCIO,).-This acid forms chlorates: if a current potash, the following reaction ensues :

3C1, + 6KHO = KCIO.+5KCI + 3H2O, is more soluble, therefore it can easily be separated from the potassium chlorate and chloride being the result; as the latter chlorate by crystallisation. It will be remembered that potassium chlorate was used in the preparation of oxygen.

chlorate when giving off oxygen be stopped, the residue will be Perchloric Acid (HCIO).-If the decomposition of potassium also perchlorate. It may be separated by means of hydrochloric found not only to contain potassium chloride and chlorate, but acid, which acts on the chlorate and decomposes it, but not on the perchlorate. From this salt the acid itself may be got.

Compounds of Chlorine and Nitrogen.-If chlorine be passed into ammonia, as has before been said, nitrogen is liberated; but after a certain quantity of sal-ammoniac has been produced, drops of an oily liquid begin to form. These are supposed to be the terchloride of nitrogen (NC1,), the most explosive and the most dangerous of chemical compounds. The experiment should never be attempted, unless all the apparatus used be of lead, and the operator dressed in a strong suit of leather, with an iron mask. A drop of this substance in a porcelain capsule was touched with the top of a fishing-rod; the violence of the explosion drove some of the porcelain through the bottom of the chair, which was of thick wood. A kindred compound of nitrogen with iodine, which is not so explosive, will be noticed.

LESSONS IN BOTANY.-XXVI. SECTION LVI-PRIMULACEAE, OR PRIMEWORTS. Characteristics: Calyx free or rarely adherent; corolla monopetalous, hypogynous or perigynous, regular; stamens inserted upon the corolla, their number equal to the parts of the corolla and opposite to its lobes; ovary unilocular; placenta central, free; ovules curved, seldom reflexed; fruit capsular; seeds numerous, dicotyledonous, albuminous.

The Primulaceae derive their name from the genus Primula, so called because its species flower in the spring. They are for the most part herbaceous, annual or perennial, having a ligneous or tuberous rhizome.

embryo straight in the axis of a fleshy albumen, lying across the hilum.

The Primulaceae principally inhabit the temperate regions of the northern hemisphere, especially Europe and Asia. They not only please the eye by the beauty of their flowers, but also

contribute something to the resources of medicine. The common primrose (Primula vulgaris) is well known to all from its yellow flowers and broad green leaves, which are seen in the hedges in sheltered nooks even before the departure of winter. The cowslip (Primula veris) is distinguished by the smallness of its flowers, which form an umbel (Fig. 205). The flowers of this plant act as a sedative, and are used in making a kind of wine of a soporific cha racter. The auricula, or bear's ear, as it

205. THE COWSLIP (PRIMULA

VERIS). 206. THE HAIRY
DATE PLUM (DIOSPYRUS
HIRSUTA).

The stem is usually subterraneous and short. The leaves are in some species radical and fasciculated, in others cauline and opposite, or verticillate, or alternate, and devoid of stipules. Flowers complete, either solitary or arranged in umbels on the summit of a shaft, or arranged in cymes springing from the axilla of the leaves, occasionally terminal in spikes. Calyx mono

sepalous, usually five partite. Corolla rotate, campanulate, or infundibuliform, contorted in æstivation, sometimes absent. Ovary composed of as many carpels as there are lobes to the calyx. Placenta free central, for the most part globular, and communicating with the summit of the ovary by arachnoid filaments. Style and stigma simple. Fruit a capsule transversely or longitudinally dehiscent. Seeds ordinarily peltate;

All the members of the primrose tribe are in great repute as ornamental plants, more especially the auriculas. From these plants, which are natives of the Alps, horticultural skill has developed several varieties. The cyclamen (Cyclamen Europaeum) possesses radical leaves which are covered with white spots above, and red on their lower surface; the corolla has a roseate tint, and in all the species of this genus the tube of the corolla is turned towards the ground, whilst its limb or free portion is directed towards the sky. The root of the cyclamen, or sowbread, is caton greedily by the

wild boars of Sicily. The name cyclamen is derived from the Greek kukλos (ku ́-klos), a circle, in allusion to the shape of the corm or bulb-like stem.

SECTION LVII.-EBENACEE, OR EBENADS.

Characteristics: Calyx free; corolla hypogynous, monopetalous; stamens sometimes equal in number to that of the lobes of the corolla, and alternating with them, sometimes double or quadruple in number; ovary many-celled, each cell uniovulate; ovules pendent from the summit of the central angle; fruit baceiform; seeds few in number, or occasionally one, dicotyledonous, albumen cartilaginous, radicle superior. Trees or shrubs possess ing an aqueous juice, and furnishing a wood which is very dense. Individuals of this natural order have alternate leaves which are coriaceous, entire, and without stipules. Flowers often incomplete, regular, axillary. Calyx three to six partite and persistent. The corolla is caducous, urceolate, slightly coriaceous, three to six partite, imbricated in æstivation. Stamens inserted at the base of the corolla, rarely in the receptacle. The berry is globular or ovoid, sometimes dry, in which case it opens by splitting.

The Ebenacea are found in tropical Asia, the Cape, Australia, and tropical America; a few species are met with in the Mediterranean district.

ovules pendent; fruit bacciform or capsular, indehiscent, loculicidal; seeds pendent, dicotyledonous, albuminous; stem ligneous.

The Oleaceae are trees or shrubs having opposite petiolate leaves without stipules. Flowers ordinarily complete and disposed in a panicle, cyme, or fascicle. Calyx persistent, four partite, sometimes absent. Corolla sometimes absent, composed of four petals, ordinarily coherent, infundibuliform or campanu late, valvate in æstivation. Anthers attached by their posterior side, ovules ordinarily twin. Fruit in some cases an unilocular drupe, as in the olive; sometimes a bilocular berry, at other times a bivalved capsule, or, lastly, a dehiscent capsule. The embryo occupies the axis of a central albumen; radicle superior. The Oleaceae inhabit temperate regions, especially in the northern hemisphere. They are rare in Asia and tropical America. The greater number of ash species (belonging to this natural order) are natives of North America. The lilacs have passed into Europe from the East. This natural order is interesting in the double respect of agriculture and horticulture. The cultivated olive (Olea sativa, Fig. 208) is a tree of little beauty, but whose utility is immense. It is a native of southern Europe. Its drupaceous fruit, the olive, is too well known to need prolonged description. The pericarp of this drupe is charged with a valuable oil, which is obtained by subjecting the fruit to heavy pressure. In the manufacture of soap and for culinary purposes olive oil is unrivalled.

The American olive (Olea Americana) bears edible drupes, as is also the case with many exotic species. The most celebrated of these is the Chinese olive (Olea fragrans), the flowers of which are mixed by the Chinese with the leaves of their tea.

trates the more evident characteristics of the Ebenaceæ.

SECTION LVIII.-AQUIFOLIACEÆ, OR HOLLYWORTS. Characteristics: Calyx free, four to six partite; corolla hypogynous, almost monopetalous; stamens four to six, alternate with the petals; ovary two to six or many celled, each cell uniovulate; ovule pendent; fruit fleshy; seed dicotyledonous; embryo straight at the summit of an abundant fleshy albumen; radicle superior; leaves opposite, simple, without stipules. The Aquifoliacea are evergreen ligneous plants, with petiolate shining leaves. The flowers are regular, axillary, and small, usually white or greenish in colour. Calyx persistent, imbricated in æstivation, as is also the corolla. Anthers adnate; ovules pendent at the summit of the central angle of each cell, and reflexed; fruit composed of agglomerated drupes.

The Aquifoliaceae are nowhere abundant, but they are more plentiful in north and equatorial America and the Cape of Good Hope than elsewhere. In tropical Asia and in Europe they are comparatively rare.

Most of the species of this natural order contain a bitter extractive principle, to which the denomination ilicine is given, and which in certain species is associated with varying proportions of an aromatic resin and a glutinous matter termed viscine. Some species are purely tonic, whilst others are purgative and emetic; a few are stimulant.

The common holly (Ilex aquifolium, Fig. 207) is a small tree distributed between the forty-second and fifty-fifth parallels of north latitude, and which in cold climates is only an unpretending shrub. It grows in greatest perfection in the mountainous forests of eastern Europe. In gardens it is cultivated for the sake of its pretty red berries and the deep green of its glossy leaves. By force of culture many varieties of the holly have been obtained, some bearing leaves devoid of spines, some having black, yellow, or white instead of red berries. Holly leaves were once employed as a febrifuge; they owe their medicinal properties to a principle termed ilicine, which admits of being extracted. Ilicine has been proposed instead of quina as a remedy for intermittent fever. From the inner bark of the holly the substance birdlime is obtained.

SECTION LIX.-OLEACEE, OR OLIVEWORTS. Characteristics: Calyx free; corolla hypogynous, regular, composed of four petals, free or coherent; stamens two, inserted upon the corolla; ovary two to five celled, bi- or pluri-ovulate;

LESSONS IN ARITHMETIC.-XXXV.

SIMPLE INTEREST.

use of it. The sum lent is called the principal, the money paid for the loan is called the interest. The sum paid for the use of the principal onght evidently to depend upon the time during which the borrower has the use of it. Interest is therefore generally paid at so much per cent. per annum; that is, for the use of every £100 of principal, so much is paid for its use during one year.

The principal and interest upon it added together constitute the amount.

If the borrower pays the interest to the lender at the expiration of every year (or as soon as, according to the agreement, it becomes due), he will evidently have to pay the same sum each year. But if he omit to do this, and retain it until he returns the principal, he will, year by year, keep in his possession a continually increasing sum belonging to the lender, upon which (if the agreement be so made) interest must be paid. In the first case the interest is said to be simple; in the second, compound.

5. To find the interest upon a given sum for a given time at a given rate per cent.

The interest for one year upon any given sum is obtained (see Art. 2 (1) in preceding lesson, page 362) by multiplying by the rate per cent., and dividing by 100.

The interest for one year having been found, the simple interest for any number of years is obtained by multiplying the one year's interest by the number of years.

EXAMPLE 1,-Find the interest on £780 10s. for 1 year at 5 per cent. The answer is r £7801, or £149. 40) 1561 (£39 Os. 6d.-Answer.

120

361

360

1

20

20

12

240

240