THE PENDULUM, No. I. THE Common pendulum is a heavy ball attached to a slight cord or thread, which may be suspended to some fixed point. This instrument, simple as it is, has been employed to determine the direction of the force of gravity, and is still used for the measurement of time. If we place the pendulum P в in any position out of the perpendicular, as PA, and let it fall freely, it will descend to B, and passing this point, will ascend on the other side to c, describing an arc B C, equal to the arc A B; it will then begin to descend, and passing B, ascend again to A. It is scarcely necessary to explain the cause of this motion, for it is evident that when the pendulum descends, its velocity increases till it reaches B, and the accelerated motion it has obtained is sufficient to carry it upwards to c. Gravity, therefore, is the governing force in the vibrations of the pendulum, and in theory, it may be considered a perpetual motion. But there are two causes which tend to destroy the motion and act effectually upon it; these are, the resistance of the air, and the friction of the suspending line upon the point of suspension. The pendulum employed for philosophical purposes, consists of a metallic weight, usually a heavy disc, so sharp round its circumference, that the resistance of the air can have little effect upon it, and the fine wire that supports it is attached to a piece of sharp steel or knife blade, which rests on plains of polished agates: with these precautions, a pendulum, notwithstanding the resistance of the air and the friction at the point of suspension, will vibrate for many hours. The time occupied in an oscillation, when it is not very considerable, is the same, whatever may be its length; or in other words, the vibrations are isochronous. This property is said to have been discovered by Galileo, the celebrated philosopher, who improved the telescope, and discovered the satellites of Jupiter. He was | | sitting one evening at the church of Pisa, and after the great chandelier was lighted up, it was left swinging, which attracted the attention of the youthful philosopher, and he, at the same time, observed that its vibrations were isochronous, that is, they were performed in equal times. By a subsequent examination, he established 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 regards the resistance of the air. This law is easily demonstrated, for if we take balls of different substances and sizes, being careful that the pendulums be of equal length, and cause them to vibrate together, it will be seen that the time occupied in a vibration will be the same. Gravity in its action upon a pendulum, causing it to oscillate, exerts its influence upon each atom of the matter which composes the ball, and therefore a single atom suspended to the end of a thread, would oscillate with the same velocity as any number of atoms combined together in a body. So, also, an atom of iron would vibrate with the same velocity as an atom of platinum, or of gold, since all masses, whatever their nature, oscillate, in the same arc, with the same velocity. These observations will tend to illustrate the principle, that gravity acts in the same manner upon all bodies. It may also be mentioned, as a third important law, that the time of the oscillations is as the square roots of the length of the pendulums: that is to say, if we take three pendulums, whose lengths are as one, four, and nine feet respectively, the time required for the oscillation of the second will be twice as long as that of the first, and the time of the oscillations of the third will be three times that of the first, because 1, 2, 3, are the square roots of 1, 4, 9, respectively. As the oscillations of the pendulum vary with its length, a certain length is required that it may beat seconds, or, in other words, vibrate sixty times in a minute. The length required in the latitude of London, is a little more than thirty-nine inches, but a pendulum that would beat seconds in Lon finition, and it is therefore necessary to cousider how far this circumstance would influence the application of the laws we have mentioned as applied to practice. don, would not do so in Paris. The observations made upon the pendulum in the island of Cayenne, by M. Ritcher, first induced philosophers to doubt whether the 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 2o 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 north pole, will not vibrate so many times at the equator. All the laws of which we have been speaking, are quite independent of the intensity of gravity, for if this force should become a hundred times greater, or a hundred times less than it is, the vibrations would still be isochronous, and their time would still have the same relation to the weight and the length of the pendulum. If gravity were doubled in intensity, the velocity of all falling bodies would be increased, and pendulums would make their vibrations quicker, but the time of the oscillations would still be as the square roots of the length of the pendulums. If gravity were to cease altogether, bodies would cease to fall, and pendulums would cease to oscil- | late, except by their acquired velocities, which would cause them to continue in motion until the motion were destroyed by friction, but there would be no reason why the pendulum should come to rest in a direction perpendicular to the surface of the earth. All the observations which have been made concerning the laws by which the vibrations of a pendulum are regulated, have reference to a simple pendulum, which is an inflexible thread without weight, having a single atom of matter attached. It must be evident that all the pendulums we are accustomed to use are compound, since it is impossible to fulfil the conditions of the de B nexed figure. The molecule b, being at a less distance from the point of suspension than the molecule B, has a tendency to vibrate with a greater velocity; but as they are joined together and must oscillate in the same time, the one is retarded and the other is accelerated, an intermediate velocity being established, and that is the velocity of the compound pendulum. But there is always a certain point in the pendulum which is neither retarded nor accelerated, and performs its oscillations as though it were alone freely suspended from the thread, and that point is called the centre of oscillation, and its distance from the point of suspension is called the length of the pendulum, which is, in fact, equal to the length of a simple pendulum, that would oscillate with the same velocity. The remarks which have been made in reference to the simplest of compound pendulums, are true in reference to all others; and as we can only employ these, there are considerable difficulties in the way of an effort to determine the intensity of gravity by their means. It is not easy to observe with accuracy the duration of an oscillation, or to determine with exactness the length of the pendulum, but both these difficulties have been overcome, and the problem has been frequently solved, first by Borda, in 1790, at the observatory of Paris, and since that period, by many English and continental philosophers, in various parts of the globe. THE WILD BOAR. Sax. vol. 2, App. iv.) 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 emillustrates 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 decondition, was accounted unclean, accord-stroy them." (See Turner's Hist. Ang. ing to the mosaic dispensation; and not The same care only so, it was held in special abhorrence, being regarded with a degree of aversion which was by no means entertained towards many animals equally unlawful to be used as food. Hence the hog is never mentioned but with disgust, or with a view to aggravate a scene of misery and degradation. In the beautiful parable of the prodigal son, who from affluence becomes overwhelmed with ruin, we find the depth of his wretchedness and destitution thus described: "He went and joined himself to a citizen of that country ; and he sent him into his fields to feed swine: and he would fain have filled his belly with the was used by the swineherd. In an ancient Saxon grant, (see as above,) the deed thus. runs: "I give food for seventy swine in that woody allotment, which the countrymen call Wulferden leh," &c. With reference to the field sports of the same people, we read, " In September is boar-hunte ing, in October is hawking." The wild hog then existed in our island as it does at the present time in the larger forests of continental Europe and Asia. In its unreclaimed condition, the hog is an active, powerful, and formidable animal; his mo tions are prompt and rapid, and his attack impetuous. Armed with enormous tusks, he strikes right and left, lacerating the body of his antagonist, and producing the severest wounds. Hunting the wild boar was one of the favourite pursuits of our forefathers, and is still kept up in Germany, where a breed of large hounds is used for driving up the game. In India, it is also among the field sports but by no means one of the least dangerous, either to the men or dogs, as it often happens that an animal infuriated by slight wounds, and closely pressed, will turn suddenly upon its pursuers, and in a moment occasion the loss of life among the party. The ancient Greeks and Romans were no less addicted to the chase of the husks that the swine did eat: and no man gave unto him." A picture this to a jew of the most abject misery and degradation! We have, however, no reason for believing that any of the adjacent nations entertained the same abhorrence of this animal as did the jews; indeed, we know that it was domesticated in many, its flesh being esteemed excellent. Among the epicurean Romans, young pig was as favourite a dish as among ourselves at the present era. When the mohammedan religion spread in the East, many of its rites and observances being derived from those enjoined on the mosaic dispensation, 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 Saxon forefathers it was an important animal, inasmuch as it was the staple flesh meat consumed in every household. England, at the time of their dominion, was largely covered with forests, and in these 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 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 safety. Nor was their task easy; the same woods were frequented by wolves, whose "So the wild boars spring furious from their den, M. JOHN DAVIS, 56, Paternoster Row, London. Price d. each, or in Monthly Parts, contairing Five Numbers in a Cover, 3d. W. TYLER, Printer, 4, Ivy Lane, St Paul's. SCRIPTURE ILLUSTRATIONS.-No. XV. THE TABLE OF SHEW-BREAD. IN the holy place, or sanctuary of the jewish temple, stood the table of shewbread. The word rendered shew-bread, means literally, "bread of faces," or of presence, from its being placed in the presence of the Lord. The table was small, and made of shittim wood, covered with plates of gold, having a little border round it, adorned with sculpture. It was two cubits long, one cubit wide, and one and a half in height. Upon this table, every sabbathday, were placed twelve loaves, with salt and incense. All are not agreed as to the manner in which the loaves of shew-bread were ranged; indeed, the form of the above VOL. III. table, and the arrangement of the loaves upon it, with the golden cup which contained the salt between them, only depends upon the authority of learned men, who have endeavoured to construct their representations from the descriptions in the Bible. The loaves were placed not on the sabbath-day before the Lord, when they also took away those which had been exposed a whole week, and which could not be lawfully eaten but by the priests. This offering was accompanied with frankincense and salt; the frankincense was burnt on the golden table when they removed the old loaves. This table, with the articles upon it, and its use, seems to typify the communion which the Lord holds with his redeemed people in his ordinances; the provisions of his house, the feasts which they sometimes are favoured with. Also, the food for their souls, which they always find when they hunger after it, and the delight he takes in their persons and services, as presented before him in Christ Jesus. CHRISTIANITY AND HEATHENISM CONTRASTED. Furthermore, they never builded or erected any hospitals, or houses of refreshing to lodge and nourish the poor, neither had the princes the almoners, to distribute their alms, as christians have. When a child was born mis-shapen and 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 and injury done to the Creator. They made account of poor men as they did of beasts; for, alas, as these poor wretches came into the market-place, and set themselves to sale, as men do their cattle, to such as bought them, standing there at offer and proffer, had full possession to do with them what they would; they had power to kill their bondmen at their pleasure, when, and how, and for what cause they thought good, and were not subject to give any account of their death, and for their so doing. They ordinarily killed their slaves and servants, when they became unprofitable unto them, and reserved such as were strong to labour, and able to do them service. It was a rule of one of the wisest among the gentiles, that we are born, not only for ourselves, but that our birth is partly for our country, partly for our parents, and partly for our friends. A goodly and golden sentence, much admired, and greatly commended, and often alleged. But if it be compared with the doctrine of Christ, and the duty of all christians, it will be found maimed in its limbs, and defective in its parts, neither having a good beginning, nor making a perfect ending. For, first of all, he prescribeth that our charity should be employed towards ourselves, which they have well marked, allowed, and followed, who say, that a well-ordered charity beginneth at himself. But this is far from the doctrine of Christ and his apostles. Christ himself commandeth us to love our neighbour as ourselves, and Paul teacheth that cha-poor slaves to band themselves in two rity seeketh not her own things. Again, he maketh mention of our country, of our parents, and of our friends, and rangeth them into good order, but what becometh of the poor? Where, or in what place of this notable sentence doth he place them? he speaketh not of them at all: let them shift as they can, they are quite forgotten, the philosopher's charity stretcheth not to them; let them sink or swim, live or die, feed or starve, it was all 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 and sustain himself and his family, than to sell himself as a slave to him that would buy him; either he killed himself, or else he perished for hunger, and died through want and famine." True it is, when they saw some men with their eyes languishing in misery, and heard them with their ears, pitifully complaining in their extremity, they were sometimes touched with commiseration and compassion towards poor persons, but they never called or accounted this duty of humanity a virtue, but only a humane passion or natural affection. Moreover, they set up sundry theatres for combats, to offer pleasure, and make pastime to the beholders, and caused their parts, one against another; then they brought them forth, causing them furiously to set one upon another with naked swords, and with naked bodies, none of them being furnished with any defensive armour; and the people assembled to see this most ungodly sport, laughed at it, and took no less pleasure to look upon it, than some men now take pleasure to see game cocks fight one with another. ATTERSOLL. FAITH AND LOVE. THAT love is not sincere which proceedeth not from, which is not a fruit of faith: those who do not first really believe on Christ, can never sincerely love Him; it is faith alone that worketh by love towards Christ and all his saints. If, therefore, any do not believe with that faith which unites them to Christ, which within purifies the heart, and is outwardly effectual in duties of obedience, whatever they may persuade themselves concerning love unto Christ, it is but a vain delusion. Where the faith of men is dead, their love will not be living and sincere; John xiv. 15; 1 Pet. i. 8. Dr. Owen. |