De silla á silla, face to face.
De tropel, in confusion; pell-
mell.

De lance, cheaply; second-
hand.

De repente, secondly.
De rodillas, on one's knees.
De consiguiente, consequently.
En conciencia, in good earnest.
De véras; de verdad, truly.
En especial, especially.
En seguida, afterward.

Mi ánimo es explicar lisa y llanamente, my intention is to explain En tanto, or, entre tanto, in the

clearly and plainly.

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; a lo menos, at least; por lo comun, in general.

66

mean time; whilst.
En alguna parte, somewhere.
En ninguna parte, nowhere.
En alguna otra parte, some-
En otra parte, elsewhere.

where else.

En ninguna otra parte, nowhere

else.

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

future.

En lo sucesivo, afterward;
hereafter.

El año que viene, next year.

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 often 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 dic-En resumen, in short; briefly. tionaries. Some of the most common are given in the follow-Hasta no mas, to the highest ing list:

A conciencia, conscientiously.

A la verdad, truly.

A vista de ojos, evidently; at a glance.

A sabiendas, knowingly.

Al seguro, securely.

as soon as

A' buen seguro, certainly.
Antes con antes,
possible.
Ahora, ahora, just now.
A cuestas, on one's shoulder
or back.

A porfia, 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 pié, on foot.

A buen hora, early; season-
ably.

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

Al revés, wrong side outwards;
on the contrary way.
A mas no poder, 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 ó á la larga, sooner or later.

|

En derechura, by the most

direct way.

En piernas, bare-legged.

Mucho tiempo ha, long time
ago.
Mañana á la noche, to-morrow
night.

No bien, no sooner; scarcely.
No mucho ha, not long since;
a short time ag
Por atras, behind.
Poco a poco, by degrees.
Poco ha, of late; lately.
Por el tanto, 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 razon, consequently.
Por fin, finally.

Por instantes, incessantly.
Por acá ó por allá, here or
Por poco, but little; nearly

Very few adverbial phrases can be literally translated from one language to another so as to give a correct idea of their meaning: thus, of those in the above list, a mas correr literally means, to more to run; algun tiempo hace, some time it makes; a 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;

A trompa y talega, helter-as, en alguna otra parte, in some other part; en ninguna parte, in no part; la semana pasada, the week past; la semana que viene, the week which comes; pocas veces, few times.

skelter; confusedly.

Bazo mano, in an underhanded

manner.

Bien como, just as.
Casi casi, very nearly.
Cuanto antes, 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 aqui para alli, to and fro,
here and there.

De antes, of old; of yore.
De continuo, continually.
De intento, purposely.
De proposito, on purpose.
De hecho, in fact; actually.
De noche, by night.
De dia, by day.

De salto, suddenly.

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; entonces, 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; aquí, here; allá, yonder;
dentro, within.

To a place; as, & adonde? whither? acá, hither.
Toward a place; as, ¿ hacia donde? whither ward?
From a place; as, de allí, 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; bastantemente, sufficiently.

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

7. Adverbs of negation and uncertainty; as, no, no; dudosa

De por sí, by one's self; apart. mente, doubtfully; acaso, quizú, perhaps.

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; the History of Greece, by J. GODKIN, 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.

Thunder is the violent explosion which succeeds the lightning in stormy clouds. The flash and the sound 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 indistinct 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 dis-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 the ear of the observer one after the other, but they produce impressions upon it of dif ferent 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 causes the unequal intensity of the sound. Fig. 486.

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 charge. 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, fills the whole horizon, without having any

definite shape or outline, like the sudden explosion of inflam-
mable substances. This lightning, which is most frequent,
seems to proceed from the depth of the clouds and to en-
lighten 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 ear 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 un-
known.

The duration of the first three sorts of lightning is not a millionth part of a second, as may be thus proved according to Professor 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. V.

Effects 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 upwards 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

794

under

from the sky. Lastly, on falling upon iron bars, it magnetises
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 oxygenous compound formed
the influence of the electric discharge, and called ozone.
The thunder shock is a violent and even mortal shock, some-
times 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
This phenomenon may be rendered
state, a shock ensuses.
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 The 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. 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.

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 con-
If the last three conditions are not fulfilled, there is a
nected with the conductor of the lightning conductor.
danger of lateral discharges, that is to say, the electric spark
may flash out between the conductor and the building, and
The rainbow is a luminous meteor which appears in the
then the conductor increases, instead of removing the danger.
clouds opposite the sun, when they are changed into the form
It consists of seven concentric arcs, presenting in
of rain.
succession the seven colours of the solar spectrum. Some-
times 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.
ber, but their colours are so faint that they escape our view.
Theory would seem to show that there may be a greater num-

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 observed in drops of dew, fountains, and indeed wherever the the inner surface of the drops. The same phenomenon is 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 connon. Those which are capable of producing it, are called cave surface, are not equally adapted to produce the phenomeefective rays.

The conductor generally goes into a 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 holen, in the ground, from about thirteen to twenty feet deep, and after having placed the foot of the conductor in it, fill 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, When a stormy cloud, electrised the contrary is the case. 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 the 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 eletricity 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. How ever, 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 explain this effectiveness, let there be a drop of water, fig. 488, into which a solar ray sa 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 b. On reaching b, 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 bg. Atg the light is again partially reflected, the remainder proceeding in a direction, 0, which forms, with the incident ray s a, an angle, called the angle of deviation. It is rays such as go, 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 corresponding 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 of 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 violet, stripe, the angle of the cone is 80° 34'.