may be rapid or slow at pleasure. For rapid intermissions, the current passes into a piece of soft iron A, which oscillates very quickly under the influence of a soft iron horse-shoe placed in the axis of the bobbin, and temporarily magnetised when the current is passing. It is this part A which, by its motion backwards and forwards, interrupts and re-establishes the inducing current, and consequently gives rise to the induced current. For slow intermissions, the oscillating piece is fastened by means of a small rod a; then, instead of passing the current through the part A, it is passed through a spring K, and through the teeth of a wooden wheel D, the teeth being of metal, and connected with the support 1 and the knob c. On turning the winch M, the current is interrupted every time the spring K ceases to touch a tooth; and as there are four teeth, there are four intermissions for each revolution, which enables one, by turning faster or slower, to vary at pleasure the number of intermissions, and consequently of shocks, in a given time.

To communicate the shocks, bring the ends of the induction wire to two knobs P and Q, to which are fastened two long copper wires covered with silk, and terminating in two exciters or, as they are usually called in this country, discharging-rods or dischargers-with glass handles TT. It is these dischargers which are applied to the organs in such a manner as to pass the current to whatever part of the body is desired.

Lastly, the apparatus has a graduator, intended to vary the

EE, intended to receive the induced current of the second order.

When a rotatory motion, more or less rapid, is communicated to the part c, as it is magnetised each time that it passes the poles of the magnets K K, it exercises upon them, through the diffusion of the magnetism, a reaction which produces a current of induction of the first order in the first wire, while this latter at the same time developes in the wire EE an induced current of the second order. These currents may be obtained separately by means of a system of parts P or Q, which are each double, but only one of which, for each system, is visible in the figure. The current then passes along copper wires wound in a spiral form upon two dischargers YY, which are held in the hand by two glass handles, and are then taken to the patient to pass the current through him. With regard to the intermissions necessary for the formation of induced currents, they are produced by means of a cylinder B and a series of parts SIDF, into the detailed description of which we

cannot now enter.

Lastly, the intensity of the shocks is regulated by means of a button screw N, which serves to bring the part o nearer to or farther from the magnets. But the principal regulator consists of two red copper cylinders HH, which surround the bobbins, and are capable of covering a larger or smaller portion of the bobbins, according to the direction given to a drawer R, to which they are attached. The shocks have the least intensity when the cylinders entirely cover the bobbins, and the greatest when they are entirely uncovered. This is to be

intensity of the current. This graduator consists of a hollow red copper cylinder, which surrounds the bobbin, and is capable of being drawn out more or less, like a drawer, by means of a graduated rod R. The intensity is greatest when the graduator is drawn out so as entirely to expose the bobbin, and it is least when it completely conceals it. This influence of the cylindrical envelope, which was observed by Messrs. Dore and Duchenne, is attributed to currents of induction which are produced in its substance.

Dr. Duchenne's Electro-Magnetic Apparatus.-Dr. Duchenne has also employed in his practice a second apparatus, in which he does not make use of the battery, but of the inducing action of a powerful magnet, in order to obtain a current, as is the case with Clarke's apparatus, of which we have given an account. The magnet KK, fig. 481, consists of two branches, united at their posterior extremities by a soft iron armature. In front of their anterior extremities there is an armature c, which is also made of soft iron, free to turn upon a horizontal axis, which is set in motion by the pinion o of a large wheel with a chain round it, and a winch M.

About the two branches of the magnets is wound a copper wire covered with silk, and intended to receive the induction of the magnets. Then upon the first wire is wound a second

explained by the currents of induction which are developed in the mass of the cylinder.

As it is not in our power to describe at length the medical effects of these apparatus, we will simply observe that they have been particularly effective in cases of paralysis.

Pulvermacher's Galvanic Chain. - M. Pulvermacher has recently devised a new sort of pile, which is remarkable for its great tension, and the facility with which it may be used. This pile, which bears a strong resemblance in the principle of its construction to the column pile described in a previous lesson, is represented in fig. 482, at the moment when the shock is communicated. Fig. 483 represents the details of its construction.

It consists of a series of small wooden cylinders м and N, upon which are wound a copper and a zinc wire by the side of one another, but without touching. At each of its ends, the zinc wire a b of the cylinder м is joined on to the copper wire of the cylinder N by means of two small copper rings inserted in the wood. Then the zinc of the cylinder N is in the same manner united to the copper of the third cylinder, and sc on throughout, in such a manner that the zinc of one cylinder always forms with the copper of the next one a couple exactly like those of the column pile. The whole thus forming a sort

of chain, which is held at the two ends, this chain is dipped in a vessel containing vinegar more or less diluted with water. The small wooden cylinders being porous, then imbibe part of the liquid, and act like the acidulated wet cloths of the column Fig. 482.

for the interruption of the current. For this purpose, it contains small clock-work machinery, which makes an oscillation of such a kind that sometimes the pole of the pile is connected internally with the side of the armature, and sometimes is not. The rapidity of the oscillations, and consequently the number of shocks, may be made to vary within certain limits by means of a small regulator o, moved by the hand. Lastly, the motion of the clock-work is produced by winding it up with a key d, which also serves as the handle of the armature. M. Pulvermacher also interrupts the current by means of a small apparatus represented in fig. 484. It consists of a glass

Fig. 484.

pile; and the chemical action produced between the zinc and the acid gives rise to a current, the intensity of which is directly proportional to the number of the couples. With a chain of twenty couples, very violent shocks are given.

Fig. 483.

M

N

To interrupt the current, which is necessary in order tc obtain shocks, M. Pulvermacher employs two methods. First, he makes use of two armatures A and B, fig. 482, to which are attached the two poles of the pile M. The armature B merely serves to establish a closer contact with the hand, but the armature A, which answers the same purpose, also serves

Fig. 485.

tube, with two copper ferrules at the ends, and two copper rods m and n. From one of these ferrules proceeds a very flexible metallic wire, terminating in a small star-shaped button. This tube being placed in the current, and the slightest motion being sufficient to make the metal wire in the tube oscillate, every time the part o touches the ferrule of the end n, the ruption is adopted when the chain is placed at rest upon a current passes, and a shock is produced. This mode of interdiseased limb, because the slightest movement makes the part o oscillate.

Physical Effects of the Galvanic Chain.-A galvanic chain of sixty couples has a tension strong enough to decompose water, even without its being acidulated. Fig. 486 shows how the experiment is arranged. At the bottom of a glass tube d, rather large and full of water, are two platinum wires connected with the poles of the battery. A second tube C, which is not fixed, is placed in the former, and is raised as the oxygen and hydrogen are liberated.

Fig. 485 represents the same experiment modified, to render it capable of setting fire to the gaseous compound as it is set at liberty. The two platinum wires are placed obliquely in the small branch of a bent tube full of water. This small branch is terminated by a very thin part a, at the extremity of which the compound of the two gases is liberated and set on fire, without, however, causing any report inside, because the small branch is quite full of water. This arrangement, which was devised by M. Ruhmkorff, may be evidently applied to more powerful batteries.

Fig. 486,

BIOGRAPHY.-No. XXV.

LAURA BRIDGMAN.

A PUPIL in the Boston Institution for the Blind has attained a wide-spread celebrity through her misfortunes, and through the efforts made by her benevolent instructor, "Principal of that Institution," to redeem her from the appalling mental darkness which the loss in early childhood of the faculties of sight, peech, and hearing, had involved her. As yet, her history is nly known through the "reports" made from time to time to

the trustees of that institution by Dr. Howe. From these we derive the following information, though not without some regret, that in the modesty which always accompanies exalted worth, he has said so little of his own noble exertions in throwing light upon that darkened spirit. Laura Bridgman was born in Hanover, New Hampshire, on the 21st of December. 1829. She is described as having been a very sprightly and pretty infant, with bright blue eyes. She was, however, so puny and feeble, until she was a year and a-half old, that her parents hardly hoped to rear her. She was subject to severe fits, which seemed to rack her frame almost beyond its

But suddenly she sickened again; her disease raged with great violence during five weeks, when her eyes and ears were inflamed, suppurated, and their contents were discharged. But though sight and hearing were gone for ever, the poor child's sufferings were not ended. The fever raged during seven weeks. "For five months she was kept in bed in a darkened room; it was a year before she could walk unsupported, and two years before she could sit up all day." It was now observed that her sense of smell was almost entirely destroyed, and consequently that her taste was much blunted. It was not until four years of age that the poor child's bodily health seemed restored, and she was able to enter upon her apprenticeship of life and the world.

But what a situation was hers! The darkness and the silence of the tomb were around her; no mother's smile called forth her answering smile; no father's voice taught her to imitate his sounds; her brothers and sisters were but forms of matter which resisted her touch, but which differed not from the furniture of the house, save in warmth and the power of locomotion, and not even in these respects from the dog or cat.

8

The small detached labels, with the same words printed upon them, were put into her hands, and she soon observed that they were similar to the ones pasted on the articles. She showed her perception of this similarity by laying the label key upon the key, and the label spoon upon the spoon. She was here encouraged by the natural sign of approbation, patting on the head.

The same process was then repeated with all the articles she could handle, and she very easily learnt to place the proper labels upon them. It was evident, however, that the only intellectual exercise was that of imitation and memory. She recollected that the label book was placed upon a book, and she repeated the process, first from imitation, next from memory, with no other motive than the love of approbation, and apparently without the intellectual perception of any relation between the things.

After a while, instead of the individual labels, letters were given to her on detached pieces of paper: they were arranged side by side, so as to spell book, key, etc., then they were mixed up in a heap, and a sign was made for her to arrange them so as to express the words book, key, etc., and she did so.

Her affections, too, began to expand, and seemed to be lavished upon the members of her family with peculiar force. But the means of communication with her were very limited; she could only be told to go to a place by being pushed, or to come to one by a sign of drawing her. Patting her gently on the head signified approbation; on the back, disapprobation.

She showed every disposition to learn, and manifestly began to use a natural language of her own. She had a sign to express her knowledge of each member of the family: as drawing her fingers down each side of her face, to allude to the whiskers of one; twirling her hand around, in imitation of the motion of a spinning-wheel, for another; and so on. But although she received all the aid that a kind mother could bestow, she soon began to give proof of the importance of language to the development of human character. Caressing and chiding will do for infants and dogs, but not for children; and by the time Laura was seven years old the moral effects of her privation began to appear. There was nothing to control her will but the absolute power of another, and humanity revolts at this. She had already begun to disregard all but the sterner nature of her father; and it was evident, that as the propensities would increase with her physical growth, so would the difficulty of restraining them increase.

At this time, Dr. Howe fortunately heard of the child, and immediately hastened to Hanover to see her. He found her with a well-formed figure, a strongly marked nervous- sanguine temperament, a large and beautifully-shaped head, and the whole system in healthy action.

Here seemed a rare opportunity of benefiting an individual, and of trying a plan for the educating of a deaf and blind person, which he had formed on seeing Julia Brace, at Hartford.

The parents were easily induced to consent to her going to Boston; and on the 4th of October, 1837, they brought her to the Institution. For a while she was much bewildered. After waiting about two weeks, until she became acquainted with her new locality, and somewhat familiar with the inmates, the

Hitherto, the process had been mechanical, and the success about as great as teaching a very knowing dog a variety of tricks. The poor child had sat in mute amazement, and truth began to flash upon her; her intellect began to work; she perceived that here was a way by which she could herself make up a sign of anything that was in her own mind, and show it to another mind; and at once her countenance lighted up with a human expression: it was no longer a dog or parrot,-it was an immortal spirit, eagerly seizing upon a new link of union with other spirits! Dr. Howe could almost fix upon the moment when this truth dawned upon her mind, and spread its light to her countenance. He saw that the great obstacle was overcome, and that henceforward nothing but patient and persevering, though plain and straightforward, efforts were to be used.

The result, thus far, is quickly related and easily conceived; but not so was the process, for many weeks of apparently unprofitable labour were passed before it was effected.

When it was said above that a sign was made, the meaning was, that the action was performed by her teacherthe feeling his hands, and then imitating the motion.

The next step was to procure a set of metal types, with the different letters of the alphabet cast upon their ends; also a board, in which were square holes, into which she could set the types, so that only the letters on their ends could be feit above the surface.

Then, on any article being handed to her-for instance, a pencil or a watch-she would select the component letters, and arrange them on her board, and read them with apparent pleasure.

She was exercised for several weeks in this way, until her vocabulary became extensive; and then the important step was taken of teaching her how to represent the different letters by the position of her fingers, instead of the cumbrous apparatus of the board and types. She accomplished this speedily and easily, for her intellect had begun to work in aid of her teacher, and her progress was rapid.

This was the period, about three months after she had commenced, that the first report of her case was made, in which it is stated, that "she has just learnt the manual alphabet as used by the deaf mutes, and it is a subject of delight and wonder to see how rapidly, correctly, and eagerly she goes on with her labours. Her teacher gives her a new object-for

instance, a pencil-first lets her examine it, and get an idea of its use, then teaches her how to spell it by making the signs for the letters with her own fingers; the child grasps his hand and feels his fingers, as the different letters are formed; she turns her head a little on one side, like a person listening closely; her lips are apart, she seems scarcely to breathe; and her countenance, at first anxious, gradually changes to a smile as she comprehends the lesson. She then holds up her tiny fingers, and spells the word in the manual alphabet; next, she takes her types and arranges her letters; and at last, to make sure she is right, she takes the whole of the types composing the word, and places them upon or in contact with the pencil, or whatever the object may be.'

The whole of the succeeding year was passed in gratifying her eager inquiries for the names of every object which she could possibly handle; in exercising her in the use of the manual alphabet; in extending, by every possible way, her knowledge of the physical relations of things, and in taking proper care of her health.

At the end of the year a report of her case was made, from which the following is an extract:-"It has been ascertained, beyond the possibility of doubt, that she cannot see a ray of light, cannot hear the least sound, and never exercises her sense of smell, if she has any. Thus her mind dwells in darkness and stillness as a closed tomb at midnight. Of beautiful sights, and sweet sounds, and pleasant odours she has no conception; nevertheless, she seems as happy and playful as a bird or a lamb; and the employment of her intellectual faculties, or acquirement of a new idea, gives her a vivid pleasure, which is plainly marked in her expressive features. She never seems to repine, but has all the buoyancy and gaiety of childhood. She is fond of fun and frolic, and when playing with the rest of the children, her shrill laugh Bounds loudest in the group.

"When left alone, she seems very happy if she has her knitting or sewing, and will busy herself for hours; if she has no occupation, she evidently amuses herself by imaginary dialogues, or by recalling past impressions; she counts with her fingers, or spells out names of things which she has recently learnt in the manual alphabet of the deaf mutes. In this lonely self-communion she seems to reason, reflect, and argue; it she spells a word wrong with the fingers of her right hand, she instantly strikes it with her left, as her teacher does, in sign of disapprobation; if right, then she pats herself upon the head, and looks pleased. She sometimes purposely spells a word wrong with the left hand, looks roguish for a moment, and laughs, and then with the right hand strikes the left, as if to correct it.

"During the year, she has attained great dexterity in the use of the manual alphabet of the deaf mutes; and she spells out the words and sentences which she knows so fast and so deftly, that only those accustomed to this language can follow with the eye the rapid motion of her fingers. But wonderful as is the rapidity with which she writes her thoughts upon the air, still more so is the ease and accuracy with which she reads the words thus written by another, grasping his hand in hers, and following every movement of his fingers, as letter after letter conveys its meaning to her mind. It is in this way that she converses with her blind playmates; and nothing can more forcibly show the power of mind in forcing matter to its purpose than a meeting between them. For if great talent and skill are necessary for two pantomimes to paint their thoughts and feelings by the movements of the body and the expression of the countenance, how much greater the difficulty when darkness shrouds them both, and the one can hear no sound! When Laura is walking through a passage-way, with her hands spread before her, she knows instantly those whom she meets, and passes them with a sign of recognition; but if it be a girl of her own age, and especially if one of her favourites, there is instantly a bright smile of recognition-a twining of arms, a grasping of hands, and a swift telegraphing upon the tiny fingers, whose rapid evolutions convey the thoughts and feelings from the outposts of one mind to those of the other. There are questions and answers, exchanges of joy or sorrow; there are kisses and caresses, just as between little children with all their senses.

During this year, and six months after she had left home,

her mother came to visit her; and the scene of their meeting was an interesting one.

The mother stood some time gazing, with overflowing eyes, upon her unfortunate child, who, all unconscious of her presence, was playing about the room. Presently Laura ran against her, and at once began feeling her hands, examining her dress, and trying to find out if she knew it; but not succeeding in this, she turned away as from a stranger, and the poor woman could not conceal the pang she felt at finding that her beloved child did not know her. She then gave Laura a string of beads which she used to wear at home, which were recognised by the child at once, who with much joy put them around her neck, and sought Dr. Howe eagerly, to say she understood the string was from her home.

The mother now tried to caress her child, but poor Laura repelled her, preferring to be with her acquaintances. Another article from home was now given her, and she began to look much interested; she examined the stranger more closely, and gave Dr. Howe to understand that she knew she came from Hanover; she even endured her caresses, but would leave her with indifference at the slightest signal. The distress of the mother was now painful to behold; for, although she had feared that she should not be recognised, the painful reality of being treated with cold indifference by a darling child was too much for woman's nature to bear.

After a while, on the mother's taking hold of her again, a vague idea seemed to flit across Laura's mind, that this could not be a stranger; she therefore very eagerly felt her hands, while her countenance assumed an expression of intense interest, she became very pale, and then suddenly red; hope seemed struggling with doubt and anxiety, and never were contending emotions more strongly depicted upon the human face. At this moment of painful uncertainty the mother drew her closer to her side, and kissed her fondly, when at once the truth flashed upon the child, and all mistrust and anxiety disappeared from her face, as with an expression of exceeding joy she eagerly nestled to the bosom of her parent, and yielded herself to her fond embraces. After this, the beads were all unheeded; the playthings which were offered to her were utterly disregarded; her playmates, for whom but a moment before she gladly left the stranger, now vainly strove to pull her from her mother; and though she yielded her usual instantaneous obedience to Dr. Howe's signal to follow him, it was evidently with painful reluctance. She clung close to him, as if bewildered and fearful; and when, after a moment, he took her to her mother, she sprang to her arms, and clung to her with eager joy.

Dr. Howe had watched the whole scene with intense interest, being desirous of learning from it all he could of the workings of her mind; but he now left them to indulge unobserved those delicious feelings which those who have known a mother's love may conceive, but which cannot be expressed.

The subsequent parting between Laura and her mother showed the affection, the intelligence, and the resolution of the child, and was thus noticed at the time: "Laura accompanied her mother to the door, clinging close to her all the way, until they arrived at the threshold, where she paused and felt around, to ascertain who was near her. Perceiving the matron, of whom she is very fond, she grasped her with one hand, holding on convulsively to her mother with the other, and thus she stood for a moment; then she dropped her mother's hand, put her handkerchief to her eyes, and turning round, clung sobbing to the matron, while her mother departed with emotions as deep as those of her child."

(1811.) It was remarkable that she could distinguish different degrees of intellect in others, and that she soon regarded a newcomer almost, with contempt when after a few days she discovered her weakness of mind. This unamiable part of her character has been more strongly developed during the past year.

She chooses for her friends and companions those children who are intelligent and can talk best with her; and she evidently dislikes to be with those who are deficient in intellect, unless, indeed, she can make them serve her purposes, which she is evidently inclined to do. She takes advantage of them and makes them wait upon her in a manner that she