Εικόνες σελίδας
Ηλεκτρ. έκδοση



sitting one evening at the church of Pisa, The common pendulum is a heavy ball and after the great chandelier was lighted attached to a slight cord or thread, which up, it was left swinging, which attracted may be suspended to some fixed point. the attention of the youthful philosopher, This instrument, simple as it is, has been and he, at the same time, observed that its employed to determine the direction of the vibrations were isochronous, that is, they force of gravity, and is still used for the were performed in equal times. By a submeasurement of time. If we place the sequent examination, he established the pendulum P B in any position out of the truth of his observation, and introduced the

pendulum for the measurement of time. The reader may easily prove the truth of this law, if he pleases, by counting the oscillations, and he will find that whether the pendulum is vibrating in an arc of four or five degrees, or in one of a tenth of a degree, an equal time is required to perform the vibration.

Another important principle in relation to the pendulum, is, that the time occupied in an oscillation is not dependent on the weight of the ball, the substance of which it

is made, or its shape, except so far as reperpendicular, as P A, and let it fall freely, gards the resistance of the air. This law is it will descend to B, and passing this point, easily demonstrated, for if we take balls of will ascend on the other side to c, describ- different substances and sizes, being careful ing an arc B C, equal to the arc a B; it will that the pendulums be of equal length, and then begin to descend, and passing B, ascend cause them to vibrate together, it will be again to A. It is scarcely necessary to ex- seen that the time occupied in a vibration plain the cause of this motion, for it is evi- will be the same. Gravity in its action dent that when the pendulum descends, its upon a pendulum, causing it to oscillate, velocity increases till it reaches B, and the exerts its influence upon each atom of the accelerated motion it has obtained is suffi- matter which composes the ball, and therecient to carry it upwards to c. Gravity, fore a single atom suspended to the end of therefore, is the governing force in the vi- a thread, would oscillate with the same vebrations of the pendulum, and in theory, it locity as any number of atoms combined may be considered a perpetual motion. But together in a boly. So, also, an atom of there are two causes which tend to destroy iron would vibrate with the same velocity the motion and act effectually upon it; as an atom of platinum, or of gold, since these are, the resistance of the air, and the all masses, whatever their nature, oscillate, friction of the suspending line upon the in the same arc, with the same velocity. point of suspension.

These observations will tend to illustrate The pendulum employed for philoso- the principle, that gravity acts in the same phical purposes, consists of a metallic manner upon all bodies. weight, usually a heavy disc, so sharp round It may also be mentioned, as a third imits circumference, that the resistance of the portant law, that the time of the oscillations air can have little effect upon it, and the is as the square roots of the length of the fine wire that supports it is attached to a pendulums: that is to say, if we take three piece of sharp steel or knife blade, which pendulums, whose lengths are as one, four, rests on plains of polished agates : with these and nine feet respectively, the time required precautions, a pendulum, notwithstanding for the oscillation of the second will be the resistance of the air and the friction at twice as long as that of the first, and the the point of suspension, will vibrate for time of the oscillations of the third will be many hours.

three times that of the first, because 1, 2, 3, The time occupied in an oscillation, are the square roots of 1, 4, 9, respectively. when it is not very considerable, is the As the oscillations of the pendulum vary same, whatever may be its length; or in with its length, a certain length is required other words, the vibrations are isochronous. that it may beat seconds, or, in other words, This property is said 10 have been dis- vibrate sixty times in a minute. The length covered by Galileo, the celebrated philo- required in the latitude of London, is a sopher, who improved the telescope, and little more than thirty-nine inches, but a discovered the satellites of Jupiter. He was pendulum that would beat seconds in Lon


don, would not do so in Paris. The ob- , finition, and it is therefore necessary to couservations made upon the pendulum in the sider how far this circumstance would inisland of Cayenne, by M. Ritcher, first in- fluence the application of the laws we have duced philosophers to doubt whether the mentioned as applied to practice. earth was perfectly spherical, and it has Let us take the simplest case of a comsince been used to determine this important pound pendulum that can be imagined, and problem. M. Ritcher found that the pen- suppose that we could obtain one that condulum of his clock moved at a rate of sisted of an inflexible thread, without 2° 28" a day less than it ought, as regu- weight, but having two heavy molecules atlated by the mean motion of the sun, and, tached to it at different distances from the to compensate for this error, he was.com- point of suspension, as shown in the anpelled to shorten his pendulum nearly oneeleventh of an inch, in order that it should make vibrations equal to those it made in Paris. This phenomenon is easily accounted for: gravity is always according to the masses, and, therefore, a double mass will have a double attraction, and a treble mass, a threefold attraction. Now it is found that a certain pendulum will beat seconds at the poles of the earth, but to make the same pendulum beat seconds at the equator, its length must be altered, which is a proof that the attraction of the earth, that is, the gravity, is not the same in both places.

A pendulum which vibrates sixty times in one minute, at the nexed figure. The molecule 6, being at a north pole, will not vibrate so many times less distance from the point of suspension at the equator.

than the molecule B, has a tendency to viAll the laws of which we have been brate with a greater velocity; but as they speaking, are quite independent of the in- are joined together and must oscillate in tensity of gravity, for if this force should the same time, the one is retarded and the become a hundred times greater, or a hun- other is accelerated, an intermediate velocity dred times less than it is, the vibrations being established, and that is the velocity of would still be isochronous, and their time the compound pendulum. But there is alwould still have the same relation to the ways a certain point in the pendulum weight and the length of the pendulum. If which is neither retarded nor accelerated, gravity were doubled in intensity, the velo- and performs its oscillations as though it city of all falling bodies would be increased, were alone freely suspended from the thread, and pendulums would make their vibrations and that point is called the centre of oscillaquicker, but the time of the oscillations tion, and its distance from the point of suswould still be as the square roots of the pension is called the length of the pendulength of the pendulums. If gravity were lum, which is, in fact, equal to the length of to cease altogether, bodies would cease to a simple pendulum, that would oscillate fall, and pendulums would cease to oscil- with the same velocity. late, except by their acquired velocities, The remarks which have been made in which would cause them to continue in reference to the simplest of compound penmotion until the motion were destroyed by dulums, are true in reference to all others ; friction, but there would be no reason why and as we can only employ these, there are the pendulum should come to rest in a di- considerable difficulties in the way of an rection perpendicular to the surface of the effort to determine the intensity of gravity earth.

by their means. It is not easy to observe All the observations which have been with accuracy the duration of an oscillation, made concerning the laws by which the vi- or to determine with exactness the length brations of a pendulum are regulated, have of the pendulum, but both these difficulties reference to a simple pendulum, which is have been overcome, and the problem has an inflexible thread without weight, having been frequently solved, first by Borda, in a single atom of matter attached. It must 1790, at the observatory of Paris, and since be evident that all the pendulums we are that period, by many English and contiaccustomed to use are compound, since it is nental philosophers, in various parts of the impossible to fulfil the conditions of the de globe.


ravages, both of the sheep and swine, were Among the many animals alluded to in very extensive. In a Saxon calendar, which the holy scriptures, one of them is that em

illustrates the agricultural labours of our blem of savage voracity and destruction, forefathers, the following statement of a the wild hog : “ The boar out of the wood shepherd's duty occurs :-“In the first part doth waste it, and the wild beast of the of the morning I drive my sheep to their field doth devour it,” Ps. lxxx. 13. This pasture, and stand over them in heat and animal, whether in a wild or domesticated in cold, with dogs, lest the wolves de condition, was accounted unclean, accord-stroy them.”. (See Turner's Hist. Ang. ing to the mosaic dispensation; and not Sax. vol. 2, App. iv.) The same care only so, it was held in special abhorrence, Saxon grant, (see as above,) the deed thus.

was used by the swineherd. In an ancient being regarded with a degree of aversion which was by no means entertained to

runs: “I give food for seventy swine in wards many animals equally unlawful to

that woody allotment, which the countrybe used as food. Hence the ,hog is never

men call Wulferden leh,” &c.

With rementioned but with disgust, or with a view ference to the field sports of the same peoto aggravate a scene of misery and degra- ple, we read, “ In September is boar-hunte dation. In the beautiful parable of the ing, in October is hawking.” The wild prodigal son, who from affluence becomes hog then existed in our island as it does at overwhelmed with ruin, we find the depth the present time in the larger forests of conof his wretchedness and destitution thus tinental Europe and Asia. In its unredescribed : “ He went and joined himself claimed condition, the hog is an active, to a citizen of that country; and he sent him powerful, and formidable animal ; his mointo his fields to feed 'swine : and he tions are prompt and rapid, and his attack would fain have filled his belly with the impetuous. Armed with enormous tusks, husks that the swine did eat: and no

he strikes right and left, lacerating the body man gave unto him.” A picture this to of his antagonist

, and producing the severest a jew of the most abject misery and de- wounds. Hunting the wild boar was one of gradation ! We have, however, no rea- the favourite pursuits of our forefathers, and son for believing that any of the adjacent

is still kept up in Germany, where a breed nations entertained the same abhorrence of of large hounds is used for driving up the this animal as did the jews ; indeed, we game. In India, it is also among the field know that it was domesticated in many, its sports : but by no means one of the least flesh being esteemed excellent. Among dangerous, either to the men or dogs, as it the epicurean Romans, young pig was as often happens that an animal infuriated by favourite a dish as among ourselves at the slight wounds, and closely pressed, will present era. When the mohammedan reli- turn suddenly upon its pursuers, and in a gion spread in the East, many of its rites moment occasion the loss of life among the and observances being derived from those party. The ancient Greeks and Romans enjoined on the mosaic dispensation, the were no less addicted to the chase of the aversion to this animal spread with it, and wild boar than our rude ancestors; it in consequence it is deemed by the moham- abounded in the woods and marshes of medans of each sect, and in every country, Italy and Greece, and is still common in as unclean. In the western portion of the old the Levant. The following picture from the world, the hog, from the earliest ages, has Iliad of Homer is so graphic, that we conconstituted no inconsiderable part of the clude with it our present details :wealth of the ruder nations. Among our “So the wild boars spring furious from their den, Saxon forefathers it was an important ani- Roused by the cry of dogs and voice of men; mal, inasmuch as it was the staple flesh Fires stream in lightning from their sanguine eyes; meat consumed in every household. Eng- On every side the crackling trees they tear, land, at the time of their dominion, was

And root the shrubs, and lay the forest bare ;

They gnash their tusks, with fire their eye-balls largely covered with forests, and in these roll, vast droves of hogs, the property of a thegn, Till some wide wound lets out their mighty soul." or ceorl, (or as we should now say, lord of

M. the manor, or large landed proprietor,) were driven to feed upon the acorns and mast, under the care of trusty thralls, or bondslaves, who were answerable for their Price jd. each, or in Monthly Parts, cuntairing Five safety. Nor was their task easy ; the same woods were frequented by wolves, whose

W. TYLER, Printer, 4, Ivy Lane, 8t Paul's.

JOHN DAVIS, 56, Paternoster Row, London.

Numbers in a Cover, 3d.

[blocks in formation]


table, and the arrangement of the loaves

upon it, with the golden cup which conIn the holy place, or sanctuary of the tained the salt between them, only depends jewish temple, stood the table of shew- upon the authority of learned men, who bread. The word rendered shew-bread, have endeavoured to construct their repremeans literally, “bread of faces,” or of sentations from the descriptions in the presence, from its being placed in the pre- Bible. The loaves were placed not on the sence of the Lord.

sabbath-day before the Lord, when they The table was small, and made of also took away those which had been exshittim wocd, covered with plates of gold, posed a whole week, and which could not having a little border round it, adorned be lawfully eaten but by the priests. This with sculpture. It was two cubits long, offering was accompanied with frankincense one cubit wide, and one and a half in and salt; the frankincense was burnt on height. Upon this table, every sabbath- the golden table when they removed the day, were placed twelve loaves, with salt old loaves. and incense. All are not agreed as to the This table, with the articles upon it, and manner in which the loaves of shew-bread its use, seems to typify the communion were ranged ; indeed, the form of the above' which the Lord holds with his redeemed



people in his ordinances; the provisions of Furthermore, they never builded or his house, the feasts which they sometimes erected any hospitals, or houses of reare favoured with. Also, the food for freshing to lodge and nourish the poor, their souls, which they always find when neither had the princes the almoners, to they hunger after it, and the delight he distribute their alms, as christians have. takes in their persons and services, as pre- | When a child was born mis-shapen and sented before him in Christ Jesus.

evil formed among them, it was killed ; yea, it was not only allowed, but commanded, to stifle and strangle it, that it should not be brought up: a cruelty and

inhumanity against nature, and a despite It was a rule of one of the wisest among and injury done to the Creator. the gentiles, that we are born, not only They made account of poor men as for ourselves, but that our birth is partly they did of beasts ; for, alas, as these poor for our country, partly for our parents, wretches came into the market-place, and and partly for our friends. A goodly set themselves to sale, as men do their and golden sentence, much admired, and cattle, to such as bought them, standing greatly. commended, and often alleged. there at offer and proffer, had full possesBut if it be compared with the doctrine sion to do with them what they would ; of Christ, and the duty of all christians, they had power to kill their bondmen at it will be found maimed in its limbs, and their pleasure, when, and how, and for defective in its parts, neither having a what cause they thought good, and were good beginning, nor making a perfect not subject to give any account of their ending. For, first of all, he prescribeth death, and for their so doing. They orthat our charity should be employed to- dinarily killed their slaves and servants, wards ourselves, which they have well when they became unprofitable unto them, marked, allowed, and followed, who say, and reserved such as were strong to lathat a well-ordered charity beginneth at bour, and able to do them service. himself. But this is far from the doctrine

Moreover, they set up sundry theatres of Christ and his apostles. Christ him for combats, to offer pleasure, and make self commandeth us to love our neighbour pastime to the beholders, and caused their as ourselves, and Paul teacheth that cha- poor slaves to band themselves in two rity seeketh not her own things.

parts, one against another; then they Again, he maketh mention of our coun- brought them forth, causing them furitry, of our parents, and of our friends, and ously to set one upon another with naked rangeth them into good order, but what swords, and with naked bodies, none of becometh of the poor? Where, or in them being furnished with any defensive what place of this notable sentence doth armour ; and the people assembled to see he place them ? he speaketh not of them this most ungodly sport, laughed at it, at all: let them shift as they can, they are and took no less pleasure to look upon it, quite forgotten, the philosopher's charity than some men now take pleasure to see stretcheth not to them; let them sink or game cocks fight one with another. swim, live or die, feed or starve, it was all

ATTERSOLL. one to him, and to that religion which he believed. Indeed, a poor person, when in extreme distress in the time of heathenism, had no other means to live That love is not sincere which proand sustain himself and his family, than ceedeth not from, which is not a fruit of to sell himself as a slave to him that faith : those who do not first really believe would buy him ; either he killed himself, on Christ, can never sincerely love Him; it or else he perished for hunger, and died is faith alone that worketh by love towards through want and famine. True it is, Christ and all his saints. If, therefore, any when they saw some men with their eyes do not believe with that faith which unites languishing in misery, and heard them them to Christ, which within purifies the with their ears, pitifully complaining in heart, and is outwardly effectual in duties their extremity, they were sometimes of obedience, whatever they may persuade touched with commiseration and com- themselves concerning love unto Christ, it passion towards poor persons, but they is but a vain delusion. Where the faith of never called or accounted this duty of men is dead, their love will not be living humanity a virtue, but only a humane and sincere ; John xiv. 15; 1 Pet. i. 8. passion or natural affection.

Dr. Owen,


« ΠροηγούμενηΣυνέχεια »