ON PHYSICS, OR NATURAL PHILOSOPHY.

No. LXIX.

(Continued from page 650.)

DYNAMICAL ELECTRICITY.

PHENOMENA OF INDUCTION.

Induction by Currents.-We owe our knowledge of this subject chiefly to the able researches of our illustrious countryman, Professor Faraday, who undertook them in the hope of obtaining electricity from ordinary magnetism, and under the influence of the consideration, that whether we adopt the beautiful theory of M. Ampère or another, or make any mental restriction whatever, it seems very extraordinary that as every electrical current is accompanied by a corresponding intensity of magnetic action at right angles to the current, good conductors of electricity, when placed within the sphere of this action, should not have a current induced through them, or some sensible effect produced, equivalent in force to such a current. That his labours resulted in success, is not only a fact of importance in the history of electrical science, but also one which strikingly illustrates the utility of physical theoriese in suggesting and directing experimental inquiries.

Professor Faraday has given the name of currents of induction, or induced currents, to instantaneous currents which are developed in metallic conductors under the influence of powerful magnets, or even that of the magnetic action of the earth.

The induction produced by currents is established by means of a bobbin with two wires. This is a cylinder of pasteboard cr wood, round which are wrapped, first a thick copper wire, and then a thinner one, both covered with silk, fig. 459. They

Fig. 459.

are wrapped round contiguously, so as to form concentric and parallel electro-dynamical helixes, the spires of which are close together, but not in metallic contact. The two ends of the wire, a and b, being connected with the extremities of the wire of a galvanometer, a voltaic current is passed along the thick wire cd, which is called the inductor. The following phenomena then take place:

1. At the moment when the wire c d begins to be traversed by a current from c towards d, for example, the deflection of the needle of the galvanometer indicates an inverse currenti.e. a current in a contrary direction to the former-in the wire a b, and one which is produced for a very short time only, for

the needle immediately returns to the zero point, and remains there as long as the inducing current passes through the wire c d.

2. At the moment when-the communications being broken off-the wire c d ceases to be traversed by a current, there is again produced in the wire a b an induced current, instantaneous like the former, but direct, i.e. in the same direction as the inducing current.

Matteucci's Apparatus.- Fig. 460 represents an apparatus invented by M. Matteucci, and constructed by M. Ruhmkorff of Paris, for the purpose of exhibing the development of currents produced by induction, whether by the discharge of a Leyden jar or the passage of a voltaic current. This apparatus consists of two glass plates about a foot in diameter, fixed vertically in two brass frames, A and B. These plates rest upon moveable supports, and are capable of being brought near each other, or removed away from each other, as may be desired. On the front side of the plate A is wound a copper wire, about one-twelfth of an inch in diameter, in a spiral form. The two ends of this wire pass through the plate, one at the centre and the other at the upper part, and terminate in small holders, like those represented at m and n, on the plate B. In these holders are placed two copper wires and d, covered with silk, which are intended to receive the inducing current. On the side of the plate в which faces the plate A, is wound, also in a spiral form, a copper wire, not quite so thick as the wire c. Its extremities terminate in the holders m and n, which receive two wires h and i, intended to transmit the induced current. The two wires wound on the surfaces of the plates A and B are not only covered with silk, but each coil is isolated from the next by a thick layer of gum-lac varnish, an indispensable condition for experimenting with the electricity of electrical machines, which is always

more difficult to isolate than that of batteries.

To show the production of the induced current by the discharge of a Leyden jar, bring one end c of the wire into connection with the external armature of the jar, and the other with the hook. Directly the spark appears, as the electricity which passes along the wire c acts by influence on the neutral fluid of the wire wound on the plate B, an instantaneous current arises in the wire. In fact, a person who holds in his hands two copper cylinders connected with the wires i and h, receives a shock, the intensity of which is greater in proportion as the plates are nearer. This experiment proves that the electricity of electrical machines is capable of giving rise to currents of induction, as well as that of the voltaic pile. M. Matteucci's apparatus also serves to demonstrate the production of induced currents by the influence of voltaic currents. For this purpose, pass the current of a battery along the inducing wire c, and at the same time connect the two wires i and h with a galvanometer. Then, at the moment when the inducing current begins or ends, the same phenomena are observed as with the bobbin (fig. 459) already described, and the needle of the multiplier is more deflected in proportion as the two plates A and B are nearer each other.

Induction by Magnets.-We have seen that the influence of a current magnetises a bar of steel; reciprocally, a magnet is capable of producing currents of induction in metallic circuits.

1. At the moment when the bar is introduced, the galvanometer indicates an instantaneous induced current in the wire, the ir verse of that which exists about the bar, comparing the baro a dynamical cylinder, as is done in the theory of Ampère.

experiments, they have employed the machine of Mr. Page, an American philosopher.

This machine consists of a strong horse-shoe magnet, before the poles of which a rectangular plate turns about an axis parallel to the two branches of the magnet, and equally distant from both. These branches are surrounded with two bobbins of long wire, the ends of which are connected with a delicate galvanometer, at a sufficient distance to be withdrawn from the action of the magnet.

metals the galvanometer always indicates the formation of With revolving plates formed of magnetic or diamagnetic 2. Directly the bar is removed, the needle of the galvano-Verdet, the observed differences depend solely upon the coninduced currents of more or less intensity. According to M. meter, which was brought back to zero, indicates a direct ductibility of the metals, and not at all upon their diamagnetic Power, as some philosophers have supposed.

induced current.

We may also establish the inductive influence of magnets by the following experiment :-Place a bar of soft iron in the single wire bobbin, and bring a strong magnet suddenly near it; the needle of the galvanometer is then deflected, returns to zero directly the magnet is fixed, and is deflected in the contrary direction on its removal. The induction is here produced by the magnetisation of the soft iron under the influence of the magnetised bar.

The same effects of induction are obtained in the wire of an

electro-magnet by turning a strongly-magnetised bar rapidly round in front of the ends of the electro-magnet, in such a manner that its poles act successively by influence on the two branches of the electro-magnet; or by forming two bobbins round a horse-shoe magnet, and passing a plate of soft iron rapidly before the poles of the magnet. The soft iron, being magnetised by influence, re-acts upon the magnet, and induced currents are successively produced in the wire in contrary directions.

Induction by Magnets in Bodies in Motion.-M. Arago, in 1824, first observed that the number of oscillations made by a needle in equal times, when it is deflected from its position of equilibrium, is very much weakened by the proximity of certain metallic substances, and particularly red copper, which is capable of reducing the number of oscillations from 300 to 4. This observation led the same philosopher, in 1825, to a fact not less unexpected, that of the tendency of a copper plate in motion to make a magnetised needle revolve.

To establish this phenomenon, arrange a moveable metallic disc on a vertical axis, and cover this disc with a glass bell, in which a magnetised needle is suspended by means of a fine thread. The needle must be separated from the disc by a thin membrane, in order that the motion of the air may not be transmitted within the bell. If the disc is subjected to a slow and uniform motion, the needle is deflected in the direction of the motion, and stops at twenty or thirty degrees from the magnetic meridian, according to the rapidity of the rotation of the disc. But if this rapidity increases, the needle is at last deflected more than ninety degrees; it is then carried along, describes an entire revolution, and follows the motion of the disc till it stops.

The effect decreases with the distance of the needle from the disc, and varies very much with the nature of the disc. The greatest effect takes place with metals; with wood, glass, water, etc., it is nothing. Mr. Babbage and Sir John Herschel have found that, representing the action of a magnet on a copper disc by 100, that upon other metals is represented by the following numbers: zinc, 95; tin, 46; lead, 25; antimony, 9; bismuth, 2. Lastly, the effect is greatly weakened if there are breaks of continuity in the disc, especially in the direction of its radii; but the same philosophers have shown that it perceptibly regains the same intensity, if the breaks are united by means of any metal whatever.

M. Arago gave no explanation of these phenomena. It was Mr. Faraday who, in 1832, first showed, by means of the galvanometer, that they were owing to currents of induction developed in the discs by the influence of the magnetised needle. The same philosopher maintains, that the magnetic action of the earth produces similar electric currents in metallic discs in motion, so that we may say that all metals in motion on the surface of the globe are traversed by currents of induction.

Since then, the phenomena of induction produced by the action of metals in motion have been studied by several philosophers both in Fraco and in America. In making their

The Induction of a Current upon itself.-When the wire along which a voltaic current passes is wound about itself like a helix, it is observed that the spirals of the helix react upon one another, so as to communicate more intensity to the current. In fact, with a Bunsen battery of several couples, for example, nothing but a scarcely perceptible spark is obtained either by closing or opening a current, if the wire which connects the two poles is short and not wound. Further, on forming part of the circuit by holding an electrode in each hand, you feel no shock at all. On the contrary, if the wire is long and wound many times round itself, so as to form a thick bobbin, the spark dwindles to nothing on closing the current, but acquires considerable intensity on opening the current; and if you form part of the circuit you feel a shock, which is more violent in proportion as the contact is more completely established with the hands.

Mr. Faraday has shown, by means of the galvanometer, that these phenomena are owing to an instantaneous current, called an extra current, which is produced in the wire connecting the in the same direction as the principal current. two poles at the moment when the connection is broken, and M. Abria, who has made many experiments on currents of induction, found that the intensity of the extra current is equal to about 72 of that of the principal current.

The effects described above acquire still greater intensity if you introduce a bar of soft iron within the bobbin, or, which bobbins of an electro-magnet. comes to the same thing, if you pass the current through the This also is a phenomenon owing to the reaction of soft iron when its magnetisation

ceases.

instantaneous, induced currents may themselves, by their inInduced Currents of Different Orders.-In spite of their being fluence upon closed circuits, give rise to fresh induced currents, these again to others, and so on, in such a manner as to produce induced currents of different orders.

of New Jersey, are established by making a series of bobbinsThese currents, which were discovered by Professor Henry, each formed of a copper wire covered with silk, and wound round itself in a spiral in the same plane, like that represented that the currents then produced in the bobbins are alternately on plate a in fig. 460-act one upon the other. It is observed in contrary directions, and that their intensity decreases in proportion as they are of a higher order.

APPARATUS FOUNDED UPON CURRENTS OF

INDUCTION.

Clarke's Apparatus.-Mr. Clarke, of London, has constructed an apparatus, by means of which all the effects of currents of magnetic induction are produced. This apparatus consists of a very powerful collection of horse-shoe magnets, fig. 461, fastened vertically to a piece of wool. In front of these magnets is an electro-magnet B B, moveable about a horizontal axis. Its bobbins are formed upon two soft iron cylinders, bound at one end by a plate v of soft iron, and at the other by a similar plate of brass. These two plates are fastened to a copper axis, terminated at one extremity by a cylinder q i, and at the other by a pulley, to which motion is communicated by means of a leather strap passing round a large wheel R.

Each bobbin is formed of a very thin copper wire, covered with silk and making as many as 1,500 turns. One end of the wire of the bobbin в joins, on the axis of rotation, an end of the wire of the bobbin B', and the two other ends terminate in a copper ferule q, which is fastened to the axis, but isolated

in two cylinders p and p' held in the hands. Then every time the current is interrupted, an instantaneous extra-current is produced in the circuit formed by the wires np, rp', and by the body, and this extra-current gives a violent shock, which is Fig. 463.

same takes place with each half of the ferule. o, and as the may be produced in currents of induction. Fig. 462 shows

liquid in which the two wires representing the electrodes are | but what are the duties arising out of man's relation to God as placed.

For physiological and chemical effects, the wire wound round the bobbins is fine, and about 1,700 to 2,000 feet upon each. For physical effects, on the contrary, the wire is thick, and about 80 or 100 feet on each bobbin. Figs. 463 and 464 show the shapes of the bobbins. The former represents the inflammation of ether, and the second the incandescence of a metallic wire o, along which passes-always in the same direction-the current going from the strip a to the strip c.

LESSONS IN MORAL SCIENCE-No. XII. DUTIES OF MAN TO THE CREATOR AS THUS MANIFESTED.

HAVING given, in a summary, the proofs of the existence and character of God, so far as reason can guide us in the inquiry, we are now prepared to consider the relation in which man stands to God, and the obligations which arise out of this relation. As man himself, in the wise and wonderful constitution of his mind and body, has been supplied with the most striking and convincing evidences of a powerful, wise, and beneficent Author of the universe; we are led at once to see, that God, as being the Creator of man, and the Giver of all his remarkable endowments, has a perfect right to claim his obedience to the utmost extent of his powers. And on taking an impartial survey of the origin of his being, of the goodness of the Creator in his various beneficent endowments, and of his continual dependence upon divine Providence, not only for the continuance of his being, faculties, and susceptibilities, but also for all those gifts necessary to his health and comfort, man cannot but feel that he is under the strongest moral obligation to obey, honour, and glorify his Maker, with his best affections and most strenuous exertions. This is the foundation of what is called the law-that moral law which is, as it were, written on the heart of every man; for what man is there, who has come to the exercise of reason, who does not perceive a clear distinction between right and wrong? And where can be found a human being, who, upon having his relation to God as his Creator set before him, does not feel in his conscience, that he is under a moral obligation to be subservient to

his will:

The general obligation on all moral agents, to serve their Creator, is evident enough. It will require some time, and careful consideration of this relation in which man stands to his Maker, to ascertain the particular duties which are obligatory on all men.

This we shall now attempt so far as reason can guide us in

this matter.

his Creator, Benefactor, and Preserver. Although the obligation to obedience arises primarily from the relations just mentioned, yet it is necessary to take into view the supreme excellence and majesty of the character of God; for if pious and devout sentiments towards God be required, it is because there is in the character of God, as exhibited in his works, something to call forth such affections from rational and rightly disposed minds. If God were not supremely excellent, it would not be reasonable to demand supreme love from his creatures, and so of other things. But as we know that God is possessed of every excellence in an infinite degree, there exists an object for every affection and sentiment towards him of which the human mind is capable. From what has been said it is evident, that in order to perform any other duties to the Creator, some knowledge of his true character is requisite. Without knowledge the rational mind cannot exercise right affections.

think man possessed when he proceeded from the hands of Supposing, then, a rational mind, such as it is reasonable to his Maker, and possessing that knowledge of his attributes which may be learnt from his works, what would be the first thoughts and feelings of the newly-created soul? In our judgment, the first feeling would be an emotion of profound veneration, or perhaps the word adoration would more strongly indicate the state of the mind, absorbed in the contemplation of a Being so august, so powerful, and so immense. This feeling, then, is one which ought to exist in every rational mind towards the Almighty. This is the true foundation of divine worship. It is the deep and solemn emotion which is the essence of the worship, which holy beings in all worlds offer unto God.

And this feeling would lead to a reverence for every thing which has any relation to God. His very name would be sacred. We have read of men of great eminence who never mentioned that name without a solemn pause, or some external token of reverence.

The duty which most naturally arises from the relation which man sustains to God, as his Creator, Benefactor, and Redeemer, is that of gratitude. This is, when strong, a very lively and impulsive feeling. It draws men along as taken captive; and yet the constraint is not painful, but pleasing. Under the influence of gratitude, men will engage in the most odious duties, and will voluntarily make the most self-denying sacrifices. Under the influence of this affection men have been willing to lay down their lives. Gratitude is, then, an important principle of man's obedience. It is true, some have attempted to degrade this principle as one which scarcely can be said to partake of the nature of virtue, because it has respect to self, and to our own interest. But though gratitude originates in the sense of benefits received by ourselves, it does not deserve to be classed with mere selfish affections. Its object is to make a return to a benefactor for favours received. It is, therefore, an elevated species of justice; for when a suitable and adequate return can be made for favours received, gratitude will not be satisfied until this is done. And in regard to the benefits received from our Creator, as an adequate compensation is utterly beyond our power, gratitude manifests itself in acknowledgment of obligation in thanksgiving and in unceasing praises. There is, however, no necessity to argue this matter; the appeal may safely be made to the feelings of every rightly constituted mind. All men who acknowledge the existence and providence of God, feel that a debt of gratitude is due to their great Benefactor.

Here it may be proper to remark, that the essence of all obedience is internal; that is, consists in the cispositions, affections and purposes of the heart. Outward actions partake of a moral nature only so far as they proceed from these internal affections. Human laws must be satisfied with external obedience, because human lawgivers cannot search the heart, nor scrutinise the motives of those who owe obedience. But even earthly judges, in administering justice, endeavour, as far as human judgment can go, to discover from what internal motives any action under examination was performed; and their decision of acquittal or condemnation is grounded on the opinion which they form of the intention and motives of the person under arraignment. Much more, then, does the moral Governor of the World require of his creatures the obedience As the mind, when uncorrupted, is so constituted as to love of the heart; for he possesses a perfect knowledge of what is and esteem whatever is excellent, and as moral excellence is in the heart of every one; and a most perfect estimate of the superior to all other amiable objects, and as God possesses nature of moral good and evil, as those qualities exist in the this excellence in an infinite degree, it is reasonable that he human heart. It seems evident, therefore, that the laws of should be esteemed above every other object. Finite minds, nature demand the highest degree of excellence of which the it is true, can never exercise love proportionate to the excelmind of man is capable. And as God possesses every moral lence of this Glorious Being; but as far as they possess the attribute in the highest perfection, it is reasonable to infer, capacity of apprehending it, and the susceptibility of affection, that man, as he came from the hands of his Creator, was en- they are under moral obligation to love God with all their dued with the seeds and principles of every moral virtue. powers. And this cannot be considered as demanding too And if the nature of man is not now found adorned with these much of the rational creature, for no other measure of affection moral excellencies, he must in the exercise of his free will have can be fixed without supposing a wrong estimate of the object, departed from his primeval state. Our present inquiry, how-or a detect of right feeling; for what is more reasonable than ever, is not whether man has fallen from his original integrity, to proportion the intensity of our affection to the excellence of

the object? But in this, also, the excellency of the object infinitely surpasses our capacity of love, so that if the mind should be enlarged a thousand-fold, so as to possess a thousand times as great a power of love and esteem as at present, the obligation to love God with this increasing capacity would be complete; and any less degree of esteem and care would be casting dishonour on God. And again, this obligation would exist, even if it were painful to come up in our affections to this high demand; but this is so far from being the fact, that man's happiness is perfect in the same proportion as his obedience is perfect. From every consideration, therefore, it is evident that man is bound by the law of his nature, and the relation which he sustains to God, to love him with his whole soul.

As the will of God is always guided by wisdom and goodness, whenever and however this will is manifested, it should be implicitly and cheerfully submitted to, even though contrary to our wishes, and even what seems best to our reason; which is submission to the providence of God.

Another duty clearly incumbent on the rational creature of God, is trust or confidence. As man is dependent, and as the supply of his necessities can be derived from no other source than from God, it is evidently his duty to place his confidence in God for every thing, believing in his goodness, faithfulness and power.

is as natural and reasonable for a dependent creature to apply This trust in God, however, involves the duty of prayer. It

are not essential to acceptable prayer. The silent breathings of desire are known to God, and will be acceptable to him. It is reasonable to believe that God never takes more complacency in his creatures, than when they come before him in the humble, reverential posture of adoration, prayer and praise. Nothing can be more evident, than that the creature should exercise benevolence or good will towards the Author of his being. Not that we can desire Him to be more excellent, more wise, more powerful, or more independent than he is; but we may rejoice in all his attributes and glory in his great ness, and be delighted with the idea of his unbounded and uninterrupted happiness; and in these elevated emotions of joy, and acts of glorying and glorifying God, it is believed that the purest, sublimest, and most constant happiness of all holy beings consists. Nothing is more evident to impartial reason, than that the glory of God should be the supreme object of the rational creature's pursuit. It is, in fact, the noblest object which can be considered. We are unable to imagine any thing more glorious for God himself to seek, than his own glory. Certainly, then, it is the highest end at which any creature can aim; and it is a sentiment entirely accordant with reason, that all the creation was produced for the purpose of exhibiting the glory of God, and man was endowed with a capacity of knowing and loving God for the very purpose of the manifestation of these perfections is what is properly glorifying his Maker. Not that any addition can be made to the essential perfection and felicity of the Eternal One; but called the glory of God.

All the duties which have been specified commend themselves, to every impartial mind, as obligatory on rational creatures; all that seems further necessary is to give a brief summary of what has been said on this subject. is not very important; for though there is an order of precedence and sequence in all our mental exercises, yet while it is unnecessary to speak of those affections which have God for their object seriatim, they are commonly combined and mingled in the conscious experience of the mind; so that in the same moment various acts and exercises appear to be simultaneous. They may, however, be all comprehended under the single term, Love, if we give a genuine meaning to that term, The summation which seems as proper as any other that suggests itself is the following:—

The order in which these devotional exercises are set down

to its Creator for what he needs as for a child thus to solicit the aid of a parent, who is believed to have the disposition and ability to bestow what it needs. Plausible objections have been raised against the duty of prayer, derived from the omniscience of God, and from his immutable purposes. But these objections possess no real validity. For although God knows perfectly well beforehand what his creatures need, yet the acknowledgment of their dependence is manifestly proper, and the offering of petitions for such things as they need has a tendency to keep up a proper sense of dependence. And as God deals with his creatures according to the nature which he has given them, it is proper that he should require of them such dispositions and acts as are becoming in dependent creatures. This, too, is in accordance with the conduct of men on whom others are dependent. The object of prayer, including praise, is to preserve in the mind a right state of feeling towards a Being to whom it owes every thing, and from whom alone blessings can be expected. The highest privilege of the most exalted creature is to enjoy communion and intercourse with the Infinite Source of all good. Prayer is the only means which man enjoys of holding immediate intercourse with his Maker. And this privilege is the highest honour which he can enjoy in the present state. So, also, it is a means of the 3. Esteem for and complacency in God's moral excellence. most sublime happiness. By this exercise he draws near to 4. Desire of Union and Communion with God, and of conGod, and when such approaches are made sincerely and affec-formity to his character. tionately on his part, it cannot be doubted that Divine com- 5. Gratitude for his goodness manifested in all creation; but munications will be vouchsafed, and the light of the Divine particularly to man, in the constitution of his soul and body, favour be lifted upon him, and the answer to his prayers and in the provision made by the providence of God for the granted by the dispensations of divine Providence toward subsistence and comfort of the human family, and of all him. living creatures.

As to the objection derived from the immutability of the Divine purposes, it arises from a narrow view of this subject, which leaves out an important part of the Divine plan. The purposes of God, though immutable, are not inconsistent with the freedom of his creatures, nor with the use and efficacy of appropriate means. The truth is, all these acts and means are included in the Divine plan. If God has decreed that a certain field shall produce a plentiful crop, he has also decreed that all the influences of sun, rain, and the necessary labour shall take place. And if he has purposed to bestow certain favours on his rational creatures, he may in the same manner purpose that these benefits shall be given in answer to prayer; so that prayer may be considered as the means by which these blessings are obtained, as truly as a plentiful crop is the effect of a skilful and laborious tillage of the ground.

As to external acts of devotion, reason and nature teach that humility and reverence in our words, attitudes and gestures are highly proper when we address our praises unto God. When we are tilled with devotional feelings, nature prompts us to give utterance to our emotions; and the use of appropriate sounds and gestures seems also to keep up and increase the feelings of the mind. These outward expressions, however,

1. Adoration, having for its object the greatness, majesty, holiness, and incomprehensibility of God.

2. Admiration, or holy wonder of the wisdom of God in the multiplied contrivances and organisations in the created universe.

6. Trust, or Confidence in God, as a benignant and kind Father and protector, who will not abandon the work of his own hands, nor be wanting in contributing to their happiness in future, as long as they are obedient to his will.

7. Acquiescence in the will of God, and submission to those dispensations which even cross the natural feelings, is an evident moral duty. Indeed, the surrender of soul and body to God, to be used and disposed of by him for his own glory, is the state of mind of which the moral faculty approves.

8. Prayer to God for such things as we need, is a duty dictated by the law of nature, including suitable expressions of our devotional feelings in words and gestures. But no creature has a right to institute or adopt any ceremonies of worship which God has not appointed.

9. Making the Glory of God the supreme end of all his actions, the object of his constant and untiring pursuit; and rejoicing and triumphing in the infinite glory, independence, immutability, and blessedness of God.

The above enumeration, it is believed, comprehends the internal acts and exercises in which the duty of man to God consists, which duties plainly arise out of the attributes of God and man's relation to him, as his Creator, Preserver, and