Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

190

[merged small][ocr errors][merged small]

It would not be more correct to say in Spanish explicar lisamente y llanamente, than it would to say in English (what the Spanish idiom literally requires), to explain clear and plainly.

Two or more words used in connexion to qualify a verb or adjective, are called an adverbial phrase or adverbial locution: such are por cierto, for certain; d lo menos, at least; por lo común, in general.

In all languages there are certain phrases used adverbially, the words of which, taken collectively, have an idiomatic meaning, but taken separately, would make no sense. Thus in English the adverbial locutions "by and by," "at least," "none at all," would signify nothing intelligible if taken literally, word by word; but as adverbial phrases, they are very expressive. It is oiten thus in Spanish: a mere literal translation of the words will do little or nothing toward assisting us to comprehend the meaning. Such phrases will generally be found explained in their adverbial sense in dietionaries. Some of the moat common are given in the following list:—

A conciencia, conscientiously.

A la verdad, truly.

A vista de ojos, evidently; at

a glance.
A sabitndas, knowingly.
A l seguro, securely.
A' buen seguro, certainly.
Antes con antes, as soon as

possible.
Ahora, ahora, just now.
A cuestas, on one's shoulder

or back.
A porfía, emulously.
A gatas, on all fours.
A coces, by dint of kicking,

by kicks.
A mas correr, with the utmost

speed.

A mas tardar, after great delay.
A la improvista, unexpectedly.
A trechos, at intervals.
A una, together; in company.
A la continua, continually.
A hecho, indiscriminately.
Al paso que, in proportion as.
A pie, on foot.

A buen hora, early; season-
ably.

A la hora, at the nick of time. Algún tiempo hace, some time since.

Alrevís, wrong side outwards;

on the contrary way. A mas no podtr, with all one's

might.

A la sordina, noiselessly; slyly.

A escondidas, or, a escondidillas, . secretly, stealthily.

Al buen punto, pointedly; opportunely.

A saltos y corcovos, by fits and starts.

A la corta 6 ala larga, sooner or later.

A ojos ctrrades, without reflection; rashly.

Al ojo, at sight.

Al punto, instantly.

A tientas, in a groping manner.

A mat tirar, to the utmost.

A tuerto i ú derecho, right or wroDg; hit or miss.

A secas y sin llover, without preparation or advice.

A solas, by one's self; in private.

A buena luz, carefully; with due examination.

A dos luces, ambiguously.

A trompa y talega, helterskelter; confusedly.

Pazo mam, in an underhanded

manner.
Bien como, just as.
Out casi, very nearly.
Cuanto dates, as soon as pos-
sible.

Cuanto tiempo, how long.
Cuando menos, at least.
Cuando mucho, at most.
De contado, readily; immedi-
ately.
De seguro, of course.
De cuando en cuando, from time

to time; now and then. De improviso, unexpectedly;

on a sudden. De aquí para alii, to and fro, here and there.

De antes, of old; of yore.

De continuo, continually.

lie intuito, purposely.

De proposito, on purpose.

De hecho, in fact; actually.

De noche, by üight.

De dia, by day.

De salto, suddenly.

Deporei, by one's self; apart.

De silla « silla, face to face. De tropel, in confusion; pellmell.

De lance, cheaply; secondhand.

De repente, secondly.

De rodillat, on one's knees.

De consiguiente, consequently.

De veras; de verdad, truly.

En conciencia, in good earnest.

En especial, especially.

En seguida, afterward.

En tanto, or, entre tanto, in the mean time; whilst.

En alguna parte, somewhere.

En ninguna parte, nowhere.

En otra parte, elsewhere.

En alguna otra parte, somewhere else.

En ninguna otra parte, nowhere else.

En cualquiera parte, any where. En adelante, forward; in the future.

En lo sucesivo, afterward;

hereafter. El año que viene, next year. En derechura, by the most

direct way. En piernas, bare-legged. En rcsimum, in short; briefly. Hasta no mas, to the highest

pitch. Hasta que, as far as. Hoy dia, or, hoy en dia, now

a-days. Hoy por hoy, this very day. Lei semana pasada, last week. La semana que cune, next week.

Mucho tiempo ha, long time ago.

Mañana d la noche, to-morrow night.

JVo bien, no sooner; scarcely. No mucho ha, not Ions since;

a short time ag Por atrás, behind. Toco ha, of late; lately. Poco á poco, by degrees. Por el tatito, on that ground;

for the reason. Por entonces, at that time. Por supuesto, of course. Por puntos, from one moment

to another. Por salto, on a sudden. Por lo largo, along. Por razón, consequently. Por Jin, finally. Por instantes, incessantly. Por poco, but little; nearly Por acá ó por allá, here or

there.

Por encima, superficially.
Pocas veces, seldom.
Sara vex, not often; seldom.
Rato ha, short time ago.
Sin sutlo, without bounds; to
excess.

Sobre seguro, confidently; securely.

Sin ion y sin son, without

rhyme or reason. Sobre manera, excessively. Sobre si, separately; selfishly. Tal vez, perhaps; once at a

time. Etta vez, once. la ha rato, some time ago.

Very few adverbial phrases can be literally translated iron one language to another so as to give a correct idea of their meaning: thus, of those in the above list, d mat correr literally means, to more to run; algún tiempo hace, some time it makes; d mas no poder, to more not to be able; de cuando en cuando, of when in when; en lo sucesivo, in that which is successive. Occasionally such a phrase may be found of which a literal translation will furnish a sufficient explanation of its meaning j as, en alguna otra parte, in some other part; en ninguna parte, in no part; la semana pasada, the week past; h semana que viene, the week which comes; pocas veces, few times.

Adverbs are variously classified according to their signification, as follows:

1. Adverbs of time; present, past, future, and indefinite.
Adverbs of time present; as, ahora, now; hoy, to-day.
Adverbs of time past; as, ayer, yesterday; entinóte, then.
Adverbs of time future; as, mañana, to-morrow.
Adverbs of time indefinite; as, cuando, when; siempre,

always; temprano, early.

2. Adverbs of place; in a place, to a place, toward a place, and from a place.

In a place; as, donde, where; aqui, here; allá, yonder;

dentro, within.
To a place; as, ¿adonde i whither? acá, hither.
Toward a place; as, ¿ hacia dondet whitherward?
Erom a place; as, de alii, thence; de donde, whence.

3. Adverbs of order; as, primero, first; finalmente, finally.

4. Adverbs of quality; as, confusamente, confusedly; bien, well.

5. Adverbs of quantity; as, poco, little; bostdniemtnle, sufficiently.

6. Adverbs of affirmation and certainty; as, si, yes; ciertamente, certainly.

7. Adverbs of negation and uncertainty; as, no, no; dudosamente, doubtfully; acaso, quizá, perhaps.

[merged small][ocr errors]

LESSONS IN READING AND ELOCUTION.
No. XXVIII.

GOD, THE CREATOR.

Cast Tout eyes upon the earth that supports us; raise them then to this immense canopy of the heavens that surrounds us,—these fathomless abysses of air and water, and these countless stars that give us light. Who is it that has suspended this globe of earth? who has laid its foundations t If it were harder, its bosom could not be laid open by man for cultivation; if it were less firm, it could not support the weight of his footsteps. From it proceed the moBt precious things: this earth, so mean and unformed, is transformed into thousands of beautiful objects that delight our eyes. In the course of one year, it becomes branches, huds, leaves, flowers, fruits, and seeds; thus renewing its bountiful favours to man. Nothing exhausts it. After yielding, for so many ages, its treasures, it experiences no decay ; it does not grow old; it still pours forth riches from its bosom.

"Who has stretched over our heads this vast and glorious arch? "What sublime objects are there! An all-powerful Hand has presented this grand spectacle to our vision.

What does the regular succession of day and night teach us? The sun has never omitted, for so many ages, to shed his blessing upon us. The dawn never fails to announce the day; and "the sun," says the Holy Book, "knows his going down." Thus it enlightens alternately both sides of the world, and sheds its rays on all. Day is the time for society and employment. Night folds the world in darkness, finishes our labours, and softens our troubles. It suspends, it calms everything. It sheds round us silence and sleep; it rests our bodies, it revives our spirits. Then day returns, and recalls man to labour, and reanimates . nil nature.

But besides the constant course of the sun, that produces day and night, during six months it approaches one pole, and during the other six, the opposite one. By this beautiful order one sun answers for the whole world. If the sun, at the same distance, were larger, it would light the whole world, but it would consume it with its heat. If it were smaller, the earth would be all ice, and could not be inhabited by men.

What compass has been stretched from heaven to earth And taken such just measurements? The changes of the sun make the variety of the seasons, which we find so delightful.

The Hand that guides this glorious work must be as skilful as it is powerful, to have made it so simple, yet so effectual; so constant and so beneficent.—Fcndon.

THE VESA MAIOl.

With what a stately and majestic step

That glorious Constellation of the North

Treads its eternal circle! going forth

Its princely way amongst the stars in slow

And silent brightness. Mighty one, all hail 1

I joy to see thee on thy glowing path

Walk, like some stout and girded giant,—stern,

Unwearied, resolute, whose toiling foot

Disdains to loiter on its destined way.

'The other tribes forsake their midnight track,
And rest their weary orbs beneath the wave.
But thou dost never close thy burning eye,
Nor stay thy steadfast step. But on, still on,
While systems change, and suns retire, and worlds
Slumber and wake, thy ceaseless march proceeds.
The near horizon tempts to rest in vain.
Thou, faithful Sentinel, dost never quit
Thy long appointed watch; but, sleepless still,
Dost guard the fixed light of the universe,
And bid the North for ever know its place.

Ages have witnessed thy devoted trust, Unchanged, unchanging. When the sons of God Sent forth that shout of joy, which rang through heaven, And echoed from the outer spheres that bound The illimitable universe,—thy voice Joined the high chorus; from thy radiant orbs The glad cry sounded, swelling to His praise Who thus had cast another sparkling gem, Little but beautiful, amid the crowd Of splendours that enrich his firmament. As thou art now, so wast thou then, the same.

Ages have rolled their course, and time grown grey; The earth has gathered to her womb again, And yet again, the myriads that were bom Of her,—uncounted, unremembered tribes. The seas have changed their beds,—the eternal hills Have stooped with age,—the solid continents Have left their banks,—and man's imperial works. The toil, pride, strength of kingdoms, which had flung Their haughty honours in the face of Heaven, As if immortal,—have been swept away,— Shattered and mouldering, buried and forgot. But time has shed no dimness on thy front, Nor touched the firmness of thy tread; youth, strength And beauty, still are thine,—as clear, as bright, As when the Almighty Former sent thee forth, Beautiful offspring of his curious skill, To watch earth's northern beacon, and proclaim The eternal chorus of Eternal Love.

I wonder as I gaze. That stream of light, Undimmed, unquenched,—just as I see it now,— Has issued from those dazzling points, through yews That go back far into eternity. Exhaustless flood! for ever spent, renewed For ever! Yea, and those refulgent drops, Which now descend upon my lifted eye, Left their far fountain twice three years* go. While those winged particles,—whose speed outstrip* The flight of thought,—were on their way, the earth Compassed its tedious circuit round and round, And in the extremes of annual change, beheld Six autumns fade, six springs renew their bloom. So far from earth those mighty orbs revolve; So vast the void through which their beams descend!

Yea, glorious lamps of God! He may have quenched
Your ancient Mimes, and bid eternal night
Rest on your spheres; and yet no tidings reach
This distant planet. Messengers still come
Laden with your far fire, and we may seem
To see your lights still burning; while their blaze
But hides the black wreck of extinguished realms,
Where anarchy and darkness long nave reigned.

Yet what is this, which to the astonished mind,
Seems measureless, and which the baffled thought
Confounds? A span, a point, in those domains,
Which the keen eye can traverse. Seven stars
Dwell in that bright cluster, and the sight
Embraces all at once; yet each from each
Recedes as far as each of them from earth.
And every star from every other burns
No less remote.

From the profound of heaven,
Untravelled even in thought, keen piercing ray*
Dart through the void, revealing to the sense
Systems and worlds unnumbered. Take the glass,
And search the skies. The opening skies pour down
Upon your gaze thick showers of sparkling fire,—
Stars, crowded, thronged, in regions so remote
That their swift beams,—the swiftest things that be,—
Have travelled centuries on their flight to earth.
Earth, Sun, and nearer Constellations! what
Are ye, amid this infinite extent
And multitude of God's most infinite works?

And these are Suns!—vast, central, living fires,
Lards of dependent systems, Kings of worlds,
That wait as satellites upon their power,
And flourish in their smile. Awake, my soul,
And meditate the wonder! Countless suns
Blaze round thee, leading forth their countless worlds t
Worlds,—in whose bosoms living things rejoice,
And drink the bliss of being, from the fount
Of all-pervading Love.

What mind can know,
What tongue can utter all their multitudes,—
Thus numberless in numberless abodes,
Known but to Thee, blest Father? Thine they are,
Thychildren, and Thy care,—and none o'erlooked
Of Thee! No, not the humblest soul that dwells
Upon the humblest globe, which wheels its course
Amid the giant glories of the sky,
Like the mean mote that dances in the beam,
Amongst the thousand mirrored lamps which fling
Their wasteful splendour from the palace wall.
None, none escape the kindness of Thy care:
All compassed underneath Thy spacious wing,
Each fed and guided by Thy powerful hand.

Tell me, ye splendid Orbs !—as from your thrones
Ye mark the rolling provinces that own
Your sway,—what beings fill those bright abodes?
How formed, how gifted; what their powers, their state,
Their happiness, their wisdom? Do they bear
The stamp of human nature? Or has God
Peopled those purer realms with lovelier forms,
And more celestial minds? Does Innocence
Still wear her native and untainted bloom?
Or has Sin breathed his deadly blight abroad,
And sowed corruption in those fairy bowers f
Has War trod o'er them with his foot of fire?
And Slavery forged his chains, and Wrath, and Hate,
And sordid Selfishness, and cruel Lust,
Leagued their base bands to tread out Light and Trutv
And scatter woe where Heaven had planted joy}
Or are they yet all Paradise, unfallen
And uncorrupt;—existence one long joy,
Without disease upon the frame, or sin
Upon the heart, or weariness of life,—
Hope never quenched, and age unknown,
And death uiifeared; while fresh and fadeless youth
Glows in the light from God's near throne of Love i

Open your lips, ye wonderful and fair!
Speak, speak! the mysteries of those living worlds
Unfold !—No language! Everlasting light,
And everlasting silence! Yet the eye
Hay read and understand. The hand of God
Has written legibly what man may know,—
The Qloey Of This Makeb. There it shines,
Ineffable, unchangeable; and man,
Bound to the surface of this pigmy globe,
Hay know and ask no more.

In other days
When death shall give the encumbered spirit wings,
Its range shall be extended; it shall roam,
Perchance, amongst those vast mysterious spheres,
Shall pass from orb to orb, and dwell in each
Familiar with its children,—learn their laws,
And share their state, and study and adore
The infinite varieties of bliss
And beauty, by the hand Divine
Lavished on all its works.

Eternity

Shall thus roll on with ever fresh delight;
No pause of pleasure or improvement; world
On world still opening to the instructed mind
An unexhausted universe, and time
But adding to its glories; while the soul,
Advancing ever to the source of light
And all perfection, lives, adores, and reigns,
In cloudless knowledge, purity, and bliss.

Henry Ware, jun.

[merged small][ocr errors][ocr errors]

Cassell's Latin Grammar. By Professors E. A. Andrews and S. Stoddard. Revised and Corrected. Price 3s. 6d. in cloth boards.

CASSELL'S SH1LLISO EDITION 07 FIRST LSSSONS IN LATIN. By Pro

fessors E. A. Andrews and 8. 8toddard. Revised and Corrected. Price is. paper covers, or ls.6d. neat cloth.

Cassell's Lessons In Latin.—Price 2s. 6d. paper covers, or 3s. neat clotb.

A Key To Cassell's Lessons In Latin. Containing Translations of all the Exercises. Price Is. paper covers, or ls.6d. clotb.

Cassell's Classical Library.—The First Volume of this Work, price Is, Cd. cloth, consists of a Latin Reader, adapted to " o- sell's First Lessons in Latin."—Volume II. comprises Latin Exercises, price 2s. neat clotb.—Volume III. contains The Acts Op The Apostles in the Original Greek, with copious Notes and a Lexicon, price 2>. Cd. neat cloth.

CASSELL'S GERMAN PRONOUNCING DICTIONARY.

In Two Parts:—1. German and English; 2. English and German. In one large handsome Octavo Volume, price 9a. cloth. The German-English Division, price 5s. in paper covers, or 5s. 6d. neat cloth; the EnglishGerman Division, 3?. 6d. paper covers, or atroitgly bound in cloth, 4s.

Cassell's Lessons In German. Parts I. and II.—Price 2s. each in paper covers, or 2s. 6d. in cloth. Two Parts bound together, price 4s. 6d.

Cassell's Eclectic German Reader: containing choice Selections from the best German Authors, in Prose and Verse. Price 2s. paper covers, or 2s. 6d. cloth.

Cassell's Lessons In German Pronunciation: consisting of easy Extracts from German Writers. Price Is. paper cover?, or Is. 6d. cloth.

feY- A Key to the above. Lessons is now ready.

Now ready,price 9s.fid. strongly bound, CASSELL'S FRENCH AND ENGLISH DICTIONARY:

Composed from the French Dictionaries of the French Academy, Eescherelle, Landais, etc.; from the English Dictionaries of Ogilvie, Johnson, Webster, etc.; and from the Technological and Scientific Dictionaries of both Languages. By Professor De Lolmb and Henry Bridqrhan, Esq.

The following are the distinctive features which render this Work superior to any of the same class now extant. It has been compiled with unusual care from tbe very best authorities. It contains correct renderings of all the. most modern words and phrases—including those of science, art, manufao lure, commerce, law, politics, etc., as well as familiar conversation —which are indispensable to a knowledge of language, but yet are rarely, if ever, to be found properly translated in any Dictionary. The idiomatic usages of the two languages—the constructions of verbs, the force of prepositions, and the changes of meaning caused by different combinations of words—are more copiously and carefully illustrated than elsewhere within the same limits. The meanings are also classified and arranged in such a manner aa to prevent the possibility of mistake. To crown all, the Work is as moderate In price as it is comprehensive in aim, accurate in detail, and superior in arrangement.—The French-English Division, price 4s. paper covers, or 5s. neat clotb; the English-French Division, price 4s. paper covers, or 5s» strongly bound.

A Series Of Lessons In French, on an entirely Novel and Simple Plan; Reprinted in a revised form from11 The Working Man's Friend." Price 6d., by post 7d. Above 30,000 copies of this work have been sold.

A Key To Cassell's Lessons In French, containing Translations of all the Exercises. Price Is* paper covers, or Is. 6d. clotb.

A Complete Manual Op Thb Frrncii Language.—By Professor Dl Lolms. Price 3s. neatly bound.

Cassell's Lessons In French. Parts I. and II.—By Professor FasOubllb. Price 2s. each in paper covers, or 2s. 6d. bound in cloth. Tbe Two Parts bound in One Volume, price 4s. 6d.

Now ready, In Two Volumes, bound in cloth, 6s. each.

THE HISTORICAL EDUCATOR.

This curious and interesting work contains the Travels and Discoveries of Herodotus, Pausanius, and others, in Egypt, the East, etc.; the History of America, by Mary Howitt; tbe History of Greece, by J. Uodkin, Esq.; complete Chronological Tables, etc. etc.; with a profusion of curious and unique Engravings.

ON PHYSICS, OR NATURAL PHILOSOPHY.
No. LXXVII.
(Continued from page 778.)
METEOROLOGY.—LUMINOUS METEORS.

Lightning is a dazzling light given out by the electric spark which is elicited from the meeting of two clouds charged with contrary electricity. The light of the flashes is white in the lower regions of the atmosphere, but in the upper regions, where the air is more rarefied, it assumes a violet tint, which is also the case, in similar circumstances, with the spark of the electrical machine.

The streaks of lightning are sometimes several miles in length. They are always zigzag in their course through the air. This phenomenon is attributed to the resistance of the air, which is compressed by the passage of a powerful discharge. The spark then deviates from a straight line, and takes the direction in which it meets with least resistance. In a vacuum it proceeds in a straight line.

There are four sorts of lightning. 1. Forked lightning, which moves with extreme velocity in the form of a track of fire, in directions which are regularly determined and exactly like those of the electric spark from electrical machines. 2. Sheet lightning, which, instead of being linear in form like the preceding, nils the whole horizon, without having any

Thunder is the violent explosion which succeeds the lightning in stormy clouds. The flash and the aound are always simultaneous, but an interval of several seconds occurs between our perception of them, owing to the fact that light travels much faster than sound.

The noise of thunder arises from the violent agitation excited in the cloud and the air by the electric discharge, an agitation rendered perceptible by the experiment with Kinnersley's Thermometer. Near the place where the lightning flashes forth, the sound of the thunder is sharp and of short duration.' Farther off we hear a series of reports rapidly succeeding one another. At a still greater distance, the noise, which is in- [ distinct and feeble at first, afterwards changes into a prolonged rolling sound of varied intensity. Various attempts have been made to explain the rolling of thunder, but none have proved perfectly satisfactory. Some attribute it to the reverberation of the sound between the earth and the clouds. Others consider lightning, not as a single electric spark, but as a series of elementary sparks, each of which gives rise to a separate report. Now, as these partial reports proceed from points at different distances, and from zones of unequal density, the consequence is that, not only do they reach ihe ear of the observer one after the other, but they produce impressions upon it of different intensity, and hence arise the duration and inequality of the rolling sound. Lastly, this phenomenon has been attributed to the zigzag course of lightning, by supposing that there is a maximum of compression of the air at each angular point, which cause* tb° unequal intensity of the sound.

[ocr errors][graphic][graphic]

defii.itc shape or outline, like the sudden explosion of inflammable substances. This lightning, which is most frequent, seems to proceed from the depth of the clouds and to enlighten the whole mass. 3. Heat lightning, so called because it appears in the nights of summer without any cloud being seen above the horizon or any sound being heard. Many hypotheses have been proposed for explaining the origin of this lightning. The most probable is, that it is nothing more than ordinary lightning, which is produced in clouds above the horizon at such distances that the reverberation of the thunder cannot reach the car of the observer. 4. Lightning which appears under the form of globes of fire. This lightning, which is sometimes visible for more than ten seconds, descends from the clouds to the earth slowly enough to be followed by the eye. These globes often rebound from the surface of the earth; at other times they separate into parts, and explode with a noise like that of several pieces of cannon. It has been remarked that it is generally under this form that lightning penetrates through buildings. The origin of lightning is unknown.

The duration of the first three sorts of lightning is not a millionth part of a second, as may be thus proved according to Profeswr Wheatstone: "Take a wheel, and get it turned with such rapidity that the spokes are invisible; on lighting them with a flash of lightning, the duration of the flash is so short, that the wheel—whatever be the velocity with which it revolves—appears completely unmoved, that is to say, its displacement is not perceptible during the continuance of the flash.

TOL. T.

Sfeelt of lightning.—The electric discharge which takes place between a stormy cloud and the earth is popularly known as the thunderbolt. The earth, under the influence of the electricity of the cloud, becomes charged with contrary electricity, and when the attraction between the two contrary electricities overcomes the resistance of the air, the spark is elicited, which is expressed in popular language by saying; that the thunderbolt falls. It is generally believed that lightning moves mpwards from below, but a contrary direction is often observed, and it is more probable that the lightning flashes from both the cloud and the earth at the same time.

According to the first law of electric attraction, lightning ought to fall upon objects which are nearest the cloud and the best conductors. And indeed it is observed that] the objects struck are trees, high buildings, and metals. For this reason it is well known to be dangerous to get under trees during a thunder-storm, particularly if the trees are good conductors, such as oaks and elms. But the danger is not so great with resinous trees, such as pines, because they are not good conductors of electricity.

The effects of lightning are very varied, and of the same nature as those of batteries, but possessing a more energetic intensity. Lightning kills men and animals, sets fire to combustible materials, melts metals and breaks to pieces bodies that are not good conductors. On penetrating the earth, it melts the silicious substances that occur in its path, and thus produces vitrified tubes, which are often called thunderbolts, and are supposed by ill-informed persons to have been hurled

155

from the sky. Lastly, on falling upon iron bars, it magnetizes them, and often reverses the poles of the compass needle.

lightning generally diffuses in its course a smell like that of sulphur on fire, or like a phosphorescent substance. This smell is attributed to an exogenous compound formed under the influence of the electric discharge, and called ozone.

The thunder shock is a violent and even mortal shock, sometimes experienced by men and animals at some considerable distance from the place where the lightning flashed forth. This phenomenon arises from the action by influence which the stormy cloud exerts upon all bodies placed within the sphere of its activity. These bodies are then, like the earth, charged with a contrary electricity to that of the cloud, but if the cloud is discharged by the recombination of its electricity with that of the earth, the influence immediately ceases, and the bodies returning suddenly from the electric to the neutral state, a shack ensuses. This phenomenon may be rendered perceptible by placing a frog near a very powerful electrical machine, when it will experience a sudden shock as each spark is elicited.

Lightning Conductors.—A lightning conductor is a rod of iron intended to afford an easy passage to the electricity of the earth, which is attracted by the contrary electricity of the stormy clouds. The invention of this invaluable protection against the injuries of lightning was the work of Franklin in 1755.

There are two distinct parts in the lightning conductor, the rod and the conductor. The rod is a straight iron bar, pointed at the end, and fastened vertically to the summit of the buildings which we wish to preserve from the lightning stroke. It is twenty or thirty feet long, and the section at the base is a square, two inches or two inches and a-half each way. The conductor is an iron bar which descends from the bottom of the rod to the earth, into which it sinks deeply. As iron bars cannot easily be made to follow all the varied directions of the outlines of buildings, it is better to make use of iron wire cords like those employed in the construction of suspension bridges. •

The conductor generally goes into it well, and, in order to establish a better connection, with the earth, has two or three branches at the end. If there is no well near, dig a hole in the ground, from about thirteen to twenty feet deep, and after having placed the foot of the conductor in it, till it up with charcoal, which is a good conductor.

The theory of lightning conductors is explained by that of electrisation by influence or induction,, and the power of the points. Franklin, who had no sooner established the identity of lightning and electricity, than he thought of applying the power of the points to lightning conductors, thought that the conductors withdrew electricity from the clouds, but, in fact, the contrary is the case. When a stormy cloud, electrised positively, for example, rises in the atmosphere, it acts by influence or induction upon the earth, repels to a distance the positive fluid, and attracts the negative fluid which is accumulated upon bodies placed on the surface of the ground, and the more abundantly in proportion as these bodies are raised to a greater height. Consequently, it is the highest which have the greatest tension, and which, therefore, are more exposed to the electric discharge. But if these bodies are armed with metallic points like tie rods of lightning conductors, the negative fluid which is attracted from the earth by the influence of the cloud, escapes into the atmosphere and neutralises the positive fluid of the cloud. Consequently, not only does a lightning conductor prevent the accumulation of electricity at the surface of the earth, but it also tends to bring the stormy clouds back to their natural state—a double effect, which is intended to prevent the thunder-stroke. However, the disengagement of electricity is sometimes so abundant, that the lightning-conductor is insufficient to discharge the earth, and accordingly the electric fluid strikes the building, but it is the conductor which receives the stroke, on account of its greater conductibility, and thus the building is preserved.

Experience has shown that a lightning conductor effectually protects a space round it, the radius of which is double the height of the conductor.

A lightning conductor, to be effectual, ought to satisfy the following conditions. 1, The rod should be thick enough not

to be melted if the lightning strikes it. 2, It ought to end in a point, to afford an easier passage for the electricity which is disengaged from the earth. For this purpose, it is customary to put a platinum or gilded copper point at the end, to prevent oxidation, or rusting, as it is popularly termed. 3, There ought to be no break from the top of the rod to the earth. 4, The connection of the rod with the earth should be as close as possible. 5, If the building armed with the lightning conductor contains pieces of metal of considerable extent, as a zinc covering or metal gutters, they must be connected with the conductor of the lightning conductor.

If the last three conditions are not fulfilled, there is a danger of lateral discharges, that is to say, the electric spark may flash out between the conductor and the building, and then the conductor increases, instead of removing the danger.

The rainbow is a luminous meteor which appears in the clouds opposite the sun, when they are changed into the form of rain. It consists of seven concentric arcs, presenting in succession the seven colours of the solar spectrum. Sometimes only one rainbow is observed, but there are generally two, an inner one, the colours of which are brighter, and an outer one, which is paler, and in which the order of the colours is reversed. In the inner bow, the red is highest, in the other violet. On some few occasions three rainbows are observed. Theory would seem to show that there may be a greater number, but their colours are so faint that they escape our view.

The phenomenon of the rainbow arises from the decomposition of the white light of the sun at the moment when it penetrates the drops of rain, and the reflection of this light on the inner surface of the drops. The same phenomenon is observed in drops of dew, fountains, and indeed wherever the light of the sun penetrates drops of water at a certain angle.

The appearance of the rainbow, and its magnitude, depend upon the position of the spectator and the height of the sun above the horizon; whence we may infer that all the rays refracted by the drops of rain, and reflected from their concave surface, are not equally adapted to produce the phenomenon. Those which are capable of producing it, are called effective rays.

To explain this effectiveness, let there be a drop of water, n, fig. 488, into which a solar ray s a passes. At the point of incidence a, part of the light is reflected by the surface of the liquid, the rest penetrates it, being at the same time decomposed, and passes through the globule in the direction a 4. On reaching 4, part of the light passes out of the drop of rain beyond, the remainder being reflected by the concave surface and returning in the direction b g. At g the light is again partially reflected, the remainder proceeding in a direction, Q o, which forms, with the incident ray s a, an angle, called the angle of deviation. It is rays such as g o, emerging from the drop on the side of the observer, which produce the sensation of the colours, provided, however, that the light is sufficiently intense.

Now it is proved by calculation, that in a series of parallel rays which fall upon the same drop, and are subject to only one reflection in its interior, the angle of deviation successively increases from the ray s" n, for which it is nothing, up to a certain limit beyond which it decreases; and that near this limit, rays entering a drop of rain parallel to each other come out parallel. From this parallelism results a pencil of light which possesses sufficient intensity to make an impression upon the retina. It is, therefore, the rays which come out parallel to each other that are effective.

The various colours which compose white light being unequally refrangible, the maximum of the angle of deviation is not the same for all. Calculation shows, that for red rays, the value of the angle of deviation correspinding to effective rays is 42° 2', and for violet rays 40° 17'. Hence it follows, that, for all drops placed in such a manner that the rays which go from the sun to the drop make, with those which go from the drop to the eye, an angle cf 42° 2', this organ receives the sensation of red, which is evidently the case with all drops situated in the circumference of the base of a cone having its axis parallel to the solar rays, and the angle contained by the two generating lines (or the two boundaries of a section through the axis of a cone) equal to 84" 4'. Such is the formation of the red stripe in the rainbow. For the yiolet stripe, the angle of the cone is 80° u',

« ΠροηγούμενηΣυνέχεια »