Part 18

It seems possible, also, that some cases of another kind may find their explanation in this direction, as, for instance, cases in which, through some strange sympathy, the brain of one person so responds to the thoughts of another that for the time being the personality of the person thus influenced may be regarded as in effect changed into that of the person producing the influence. Thus, in one singular case cited by Dr. Carpenter, a lady was 'metamorphosed into the worthy clergyman on whose ministry she attended, and with whom she was personally intimate. I shall never forget,' he says, 'the intensity of the lackadaisical tone in which she replied to the matrimonial counsels of the physician to whom he (she) had been led to give a long detail of his (her) hypochondriacal symptoms: "A wife for a dying man, doctor." No intentional simulation could have approached the exactness of the imitation alike in tone, manners, and language, which spontaneously proceeded from the idea with which the fair subject was possessed, that she herself experienced all the discomforts whose detail she had doubtless frequently heard from the real sufferer.' The same lady, at Dr. Carpenter's request, mentally 'ascended in a balloon and proceded to the North Pole in search of Sir John Franklin, whom she found alive, and her description of his appearance and that of his companions was given with an inimitable expression of sorrow and pity.'

It appears to us that very great interest attaches to the researches made by Prof. Barrett into cases of this kind, and that it is in this direction we are to look for the explanation of many mysterious phenomena formerly regarded as supernatural, but probably all admitting (at least all that have been properly authenticated) of being interpreted so soon as the circumstances on which consciousness depends shall have been determined. Thus the following account of experiments made at the village school in Westmeath seem especially suggestive: 'Selecting some of the village children, and placing them in a quiet room, giving each some small object to look at steadily, he found one amongst the number who readily passed into a state of reverie. In that state the subject could be made to believe the most extravagant statements, such as that the table was a mountain, a chair a pony, a mark on the floor, an insuperable obstacle. The girl thus mesmerised passed on the second occasion into a state of deeper sleep or trance, wherein no sensation whatever was experienced, unless accompanied by pressure on the eyebrows of the subject. When the pressure of the fingers was removed, the girl fell back in her chair utterly unconscious of all around, and had lost all control over her voluntary muscles. On reapplying the pressure, though her eyes remained closed, she sat up and answered questions readily, but the manner in which she answered them, her acts and expressions, were capable of wonderful diversity, by merely altering the place on the head where the pressure was applied. So sudden and marked were the changes produced by a movement of the fingers, that the operation seemed very like playing on some musical instrument. On a third occasion the subject, after passing through these, which have been termed the biological and phrenological states, became at length keenly and wonderfully sensitive to the voice and acts of the operator. It was impossible for the latter to call the girl by her name, however faintly and inaudibly to those around, without at once eliciting a prompt response. If the operator tasted, smelt, or touched anything, or experienced any sudden sensation of warmth or cold, a corresponding effect was produced on the subject, though nothing was said, nor could the subject have seen what had occurred to the operator. To be assured of this he bandaged the girl's eyes with great care, and the operator having gone behind the girl to the other end of the room, he watched him and the girl, and repeatedly assured himself of this fact.' Thus far, Professor Barrett's observations, depending in part on what the operator experienced, may be open to just so much doubt as may affect our opinion of the veracity of a person unknown; but in what follows we have his own experience alone to consider. 'Having mesmerised the girl himself, he took a card at random from a pack which was in a drawer in another room. Glancing at the card to see what it was, he placed it within a book, and in that state brought it to the girl. Giving her the closed book, he asked her to tell him what he had put within its leaves. She held the book close to the side of her head, and said, 'I see something inside with red spots on it; and she afterwards said there were five red spots on it. The card was the five of diamonds. The same result occurred with another card; and when an Irish bank-note was substituted for the card, she said, 'Oh, now I see a number of heads--so many that I cannot count them.' He found that she sometimes failed to guess correctly, asserting that the things were dim; and she could give no information of what was within the book unless he had previously known what it was himself. More remarkable still, he asked her to go in imagination to Regent Street, in London, and tell him what shops she had seen. The girl had never been out of her remote village, but she correctly described to him Mr. Ladd's shop, of which he happened to be thinking, and mentioned the large clock that overhangs the entrance to Beak Street. In many other cases he convinced himself that the existence of a distinct idea in his own mind gave rise to an image of the idea (that is, to a corresponding image) on the mind of the subject; not always a clear image, but one that could not fail to be recognised as a more or less distorted reflection of his own thought.' It is important to notice the limit which a scientific observer thus recognised in the range of the subjects' perception. It has been stated that subjects in this condition have been able to describe occurrences not known to any person, which yet have been subsequently verified. Although some narratives of the kind have come from persons not likely to relate what they knew to be untrue, the possibility of error outweighs the probability that such narratives can really be true. There is a form of unconscious cerebration by which untruthful narratives come to be concocted in the mind. For instance, Dr. Carpenter heard a scrupulously conscientious lady asseverate that a table 'rapped' when nobody was within a yard of it; but the story was disproved by the lady herself, who found from her note-book, recording what really took place, that the hands of six persons rested on the table when it rapped. And apart from the unconscious fiction-producing power of the mind, there is always the possibility, nay, often the extreme probability, that the facts of a case may be misunderstood. Persons may be supposed to know nothing about an event who have been conscious of its every detail; nay, a person may himself be unconscious of his having known, and in fact of his really knowing, of a particular event. Dual consciousness in this particular sense is a quite common experience, as, for instance, when a story is told us which we receive at first as new, until gradually the recollection dawns upon us and becomes momentarily clearer and clearer, not only that we have heard it before, but of the circumstances under which we heard it, and even of details which the narrator from whom a few moments before we receive it as a new story has omitted to mention.

The most important of all the questions depending on dual consciousness is one into which I could not properly enter at any length in these pages--the question, namely, of the relation between the condition of the brain and responsibility, whether such responsibility be considered with reference to human laws or to a higher and all-knowing tribunal. But there are some points not wanting in interest which may be here more properly considered.

In the first place it is to be noticed that a person who has passed into a state of abnormal consciousness, or who is in the habit of doing so, can have no knowledge of the fact in his normal condition except from the information of others. The boy at Norwood might be told of what he had said and done while in his less usual condition, but so far as any experience of his own was concerned, he might during all that time have been in a profound sleep. Similarly of all the other cases. So that we have here the singular circumstance to consider, that a person may have to depend on the information of others respecting his own behaviour--not during sleep or mental aberration or ordinary absence of mind--but (in some cases at least) while in possession of all his faculties and unquestionably responsible for his actions. Not only might a person find himself thus held responsible for actions of which he had no knowledge, and perhaps undeservedly blamed or condemned, but he might find himself regarded as untruthful because of his perfectly honest denial of all knowledge of the conduct attributed to him. If such cases were common, again, it would not improbably happen that the simulation of dual consciousness would become a frequent means of attempting to evade responsibility.

Another curious point to be noticed is this. Supposing one subject to alternations of consciousness were told that in his abnormal condition he suffered intense pain or mental anguish in consequence of particular actions during his normal state, how far would he be influenced to refrain from such actions by the fear of causing pain or sorrow to his 'double,' a being of whose pains and sorrows, nay, of whose very existence, he was unconscious? In ordinary life a man refrains from particular actions which have been followed by unpleasant consequences, reasoning, in some cases, 'I will not do so-and-so, because I suffered on such and such occasions when I did so' (we set religious considerations entirely on one side by assuming that the particular actions are not contrary to any moral law), in others, 'I will not do so-and-so because my so doing on former occasions has caused trouble to my friend A or B:' but it is strange to imagine any one reasoning, 'I will not do so-and-so because my so doing on former occasions has caused my second self to experience pain and anguish, of which I myself have not the slightest recollection.' A man may care for his own well-being, or be unwilling to bring trouble on his friends, but who is that second self that his troubles should excite the sympathy of his fellow-consciousness? The considerations here touched on are not so entirely beyond ordinary experience as might be supposed. It may happen to any man to have occasion to enter into an apparently unconscious condition during which in reality severe pains may be suffered by another self, though on his return to his ordinary condition no recollection of those pains may remain, and though to all appearance he has been all the time in a state of absolute stupor; and it may be a reasonable question, not perhaps whether he or his double shall suffer such pains, but whether the body which both inhabit will suffer while he is unconscious, or while that other consciousness comes into existence. That this is no imaginary supposition is shown by several cases in Abercrombie's treatise on the 'Intellectual Powers.' Take, for instance, the following narrative:--'A boy,' he tells us, 'at the age of four suffered fracture of the skull, for which he underwent the operation of the trepan. He was at the time in a state of perfect stupor, and after his recovery retained no recollection either of the accident or of the operation. At the age of fifteen, however, during the delirium of fever, he gave his mother an account of the operation, and the persons who were present at it, with a correct description of their dress, and other minute particulars. He had never been observed to allude to it before; and no means were known by which he could have acquired the circumstances which he mentioned.' Suppose one day a person in the delirium of fever or under some other exciting cause should describe the tortures experienced during some operation, when, under the influence of anæsthetics, he had appeared to all around to be totally unconscious, dwelling in a special manner perhaps on the horror of pains accompanied by utter powerlessness to shriek or groan, or even to move; how far would the possibilities suggested by such a narrative influence one who had a painful operation to undergo, knowing as he would quite certainly, that whatever pains his alter ego might have to suffer, not the slightest recollection of them would remain in his ordinary condition?

There is indeed almost as strange a mystery in unconsciousness as there is in the phenomena of dual consciousness. The man who has passed for a time into unconsciousness through a blow, or fall, or fit, cannot help asking himself like Bernard Langdon in that weird tale, Elsie Venner, 'Where was the mind, the soul, the thinking principle all that time?' It is irresistibly borne in upon him that he has been dead for a time. As Holmes reasons, 'a man is stunned by a blow and becomes unconscious, another gets a harder blow and it kills him. Does he become unconscious too? If so, when, and how does he come to his consciousness? The man who has had a slight and moderate blow comes to himself when the immediate shock passes off and the organs begin to work again, or when a bit of the skull is "pried" up, if that happens to be broken. Suppose the blow is hard enough to spoil the brain and stop the play of the organs, what happens then?' So far as physical science is concerned, there is no answer to this question; but physical science does not as yet comprehend all the knowable, and the knowable comprehends not all that has been, is, and will be. What we know and can know is nothing, the unknown and the unknowable are alike infinite.

FOOTNOTES:

ELECTRIC LIGHTING.

Although we certainly have no reason to complain of the infrequency of attempts in newspapers, &c., as well as in scientific journals, to explain the principles on which electric lighting depends, it does not seem that very clear ideas are entertained on this subject by unscientific persons. Nor is this, perhaps, to be wondered at, when we observe that in nearly all the explanations which have appeared, technical expressions are quite freely used, while those matters about which the general reader especially desires information are passed over as points with which every one is familiar. Now, without going quite so far as to say that there is no exaggeration in the picture presented some time back in Punch, of one who asked whether the electric fluid was 'anything like beer, for instance,' I may confidently assert that the very vaguest notions are entertained by nine-tenths of those who hear about the electric light, respecting the nature of electricity. Of course, I am not here referring to the doubts and difficulties of electricians on this subject. It is well known that Faraday, after a life of research into electrical phenomena, said that when he had studied electricity for a few years he thought he understood much, but when he had nearly finished his observational work he found he knew nothing. In the sense in which Faraday spoke, the most advanced students of science must admit that they know nothing about electricity. But the greater number of those who read about the electric light are not familiar even with electrical phenomena, as distinguished from the interpretation of such phenomena. I am satisfied that there is no exaggeration in a passage which appeared recently in the 'Table Talk' of the Gentleman's Magazine, describing an account of the electric light as obtained from some new kind of gas, carried in pipes from central reservoirs, and chiefly differing from common gas in this, that the heat resulting from its consumption melted ordinary burners, so that only burners of carbon or platinum could be safely employed.

I do not propose here to discuss, or even to describe (in the proper sense of the word) the various methods of electric lighting which have been either used or suggested. What I wish to do is to give a simple explanation of the general principles on which illumination by electricity depends, and to consider the advantages which this method of illumination appears to promise or possess.

Novel as the idea of using electricity for illuminating large spaces may appear to many, we have all of us been long familiar with the fact that electricity is capable of replacing the darkness of night by the light of broad day over areas far larger than those which our electricians hope to illuminate. The lightning flash makes in an instant every object visible on the darkest night, not only in the open air, but in the interior of carefully darkened rooms. Nay, even if the shutters of a room are carefully closed and the room strongly illuminated, the lightning flash can yet be clearly recognised. And it must be remembered that though the suddenness of the flash makes us the more readily perceive it (under such circumstances, for instance), yet its short duration diminishes its apparent intensity. This may appear a contradiction in terms, but is not so in reality. The perception that there has been a sudden lighting up of the sky or of a room, is distinct from the recognition of the actual intensity of the illumination thus momentarily produced. Now it is quite certain that the eye cannot assign less than a twenty-fifth of a second or so to the duration of the lightning flash, for, as Newton long since showed, the retina retains the sensation of light for at least this interval after the light has disappeared. It is equally certain, from Wheatstone's experiments, that the lightning flash does not actually endure for the 100,000th part of a second. Adopting this last number, though it falls far short of the truth--the actual duration being probably less than 1,000,000th of a second--we see that so far as the eye is concerned, an amount of light which was really emitted during the 100,000th part of a second is by the eye judged to have been emitted during an interval 4,000 times as long. It is certain, then, that the eye's estimate of the intensity of the illumination resulting from a lightning flash is far short of the truth. This is equally true even in those cases where lightning is said to be for awhile continuous. If the flashes for a time succeed each other at less intervals than a twenty-fifth of a second, the illumination will appear continuous. But it is not really so. To be so, the flashes should succeed each other at the rate of at least 100,000, and probably of more than 1,000,000 per second.

While the lightning flash shows the brilliancy which the electric illumination can attain, it shows also the intense heat resulting from the electric discharge. This might, indeed, be inferred simply from the brilliancy of the light, since we know that this brilliancy can only be due to the intense heat to which the particles along the track of the electric flash have been raised. But it is shown in a more convincing manner to ordinary apprehension by the effects which the lightning flash produces where--in the common way of speaking--it strikes. The least fusible substances are melted. Effects are produced also which, though at first not seemingly attributable to intense heat, yet in reality can be no otherwise explained. Thus, when the trunk of a tree is torn into fragments by the lightning stroke, though the tree is scorched and blackened, a small amount of heat would account for that particular effect, while the destruction of the tree seems attributable to mechanical causes. It is, indeed, from effects such as these that the idea of the fall of thunderbolts has doubtless had its origin, the notion being that some material substance has struck the body thus shattered or destroyed. In reality, however, such destructive effects are due entirely to the intense heat excited during the passage of the electricity. Thus, in the case of a tree destroyed by lightning, the shattering of boughs and trunk results from the sudden conversion of the moisture of the tree (that is, the moisture present in the substance of the tree) into steam, a change accompanied of course by great and sudden expansion. The tree is as certainly destroyed by the effects of heat as is a boiler which has burst, though in each case the expansive power of steam directly works the mischief.

It is the more useful for our present purpose thus to note at the outset both the illuminating and the heating power of the lightning flash (or rather of the electric discharge), because, as will presently be seen, the electric light, while in all cases depending on intensity of heat, may either be obtained in the form of a series of flashes succeeding each other so quickly as to be to all intents and purposes continuous, or from the incandescence of some suitable substance in the path of the electric current.

Let us now consider briefly the general nature of electrical phenomena, or at least of those electrical phenomena which are related to our present subject.

Formerly, when light was supposed to be a material emanation, and heat was regarded as an actual fluid, electricity was in like manner regarded as some subtle fluid which could be generated or dispersed in various ways. At present, it is safer to speak of electricity as a state or condition of matter. If it were not that some very eminent electricians (and one especially whose eminence as a practical electrician is very great) are said to believe still that there is such a thing as an electric fluid, we should have simply asserted that in the present position of scientific research, with the known velocity at which the so-called electric current flows, and the known relations between electricity, heat, and light, the theory of an electric fluid is altogether untenable. It will suffice, however, under the actual circumstances, to speak simply of electrical properties, without expressing any definite opinion respecting their interpretation.

A certain property, called electricity, is excited in any substance by any cause affecting the condition of the substance, whether that cause be mechanical, chemical, thermal, or otherwise. No change can take place in the physical condition of any body without the generation of a greater or less amount of electricity, although in far the greater number of cases there may be no obvious evidence of the fact, while in many cases no evidence may be obtainable even by the use of the most delicate scientific tests.

I have spoken here of the generation of a greater or less amount of electricity, but in reality it would be more correct to speak simply of a change in the electrical condition of the substance. Electricians speak of positive and negative electricity as though there actually were two distinct forms of this peculiar property of matter. But it may be questioned whether it would not be more correct to speak of electricity as we do of heat. We might speak of cold as negative heat precisely as electricians give the name of negative electricity to a relative deficiency of what they call positive electricity; but in the case of heat and cold it is found more convenient, and is more correct, to speak of different degrees of one and the same quality. The difficulty in the case of electricity is that at present science has no means of deciding whether positive or negative electricity has in reality the better claim to be regarded as absolute electricity. Making comparison between electrical and thermal relations, the process which we call the generation of positive electricity may in reality involve the dispersion of absolute electricity, and so correspond to cooling, not to heating. In this case the generation of what we call negative electricity would in reality be the positive process. However, it is not necessary to discuss this point, nor can any error arise from the use of the ordinary method of expression, so long as we carefully hold in remembrance that it is only employed for convenience, and must not be regarded as scientifically precise.

Electricity may be excited, as I have said, in many ways. With the ordinary electrical machine it is excited by the friction of a glass disc or cylinder against suitable rubbers of leather and silk. The galvanic battery developes electricity by the chemical action of acid solutions on metal plates. We may speak of the electricity generated by a machine as frictional electricity, and of that generated by a galvanic battery as voltaic electricity; in reality, however, these are not different kinds of electricity, but one and the same property developed in different ways. The same also is the case with magnetic electricity, of which I shall presently have much to say: it is electricity produced by means of magnets, but is in no respect different from frictional or voltaic electricity. Of course, however, it will be understood that for special purposes one method of producing electricity may be more advantageously used than another. Just as heat produced by burning coal is more convenient for a number of purposes than heat produced by burning wood, though there is no scientific distinction between coal-produced heat and wood-produced heat, so for some purposes voltaic electricity is more convenient than frictional electricity, though there is no real distinction between them.

Every one knows that when by means of an ordinary electrical machine electricity has been generated in sufficient quantity and under suitable conditions to prevent its dispersion, a spark of intense brilliancy and greater or less length, according to the amount of electricity thus collected, can be obtained when some body, not similarly electrified, is brought near to what is called the conductor of the machine. The old-fashioned explanation, still repeated in many of our books, ran somewhat as follows:--'The positive electricity of the conductor decomposes the neutral or mixed fluid of the body, attracting the negative fluid and repelling the positive. When the tension of the opposite electricities is great enough to overcome the resistance of the air, they re-combine, the spark resulting from the heat generated in the process of their combination.' This explanation is all very well; but it assumes much that is in reality by no means certain, or even likely. All we know is, that whereas before the spark is seen the electrical conditions of the conductor and the object presented to it were different, they are no longer different after the flashing forth of the spark. It is as though a certain line (straight, crooked, or branched) in the air had formed a channel of communication by which electricity had passed, either from the conductor to the object or from the object to the conductor,--or possibly in both directions, two different kinds of electricity existing (before the flash) in the conductor and the object, as the old-fashioned explanation assumes. Again, we know that the passage of electricity along the air-track supposing there really is such a passage, but in any case the observed change in the relative electrical conditions of the conductor and the object, is accompanied by the generation of an intense heat along the aërial track where the spark is seen.

In the case of electricity generated by means of a galvanic battery, we do not note the same phenomena unless the battery is a strong one. We have in such a battery a steady source of electricity, but unless the battery is powerful, the electricity is of low intensity, and not competent to produce the most striking phenomena of frictional electricity. For instance, voltaic electricity, as used in telegraphic communication, is far weaker than that obtained from even a small electrical machine. What is called the positive extremity of the battery neither gives a spark, nor attracts light bodies. The same is true of the other, or negative extremity. The difference of the condition of these extremities can only be ascertained by delicate tests--the deflections of the needle, in fact, by which telegraphic communications are made, may in reality be regarded as the indications of a very delicate electro-cope.

But when the strength of a galvanic battery is sufficiently great, or, in other words, when the total amount of chemical action brought into play to generate electricity is sufficient, we obtain voltaic electricity not only surpassing in intensity what can be obtained from electrical machines, but capable of producing spark after spark in a succession so exceedingly rapid that the light is to all intents and purposes continuous.

Without considering the details of the construction of a galvanic battery, which would occupy more space than can here be spared, and even with fullest explanation would scarcely be intelligible (except to those already familiar with the subject), unless illustrations unsuited to these pages were employed, let us consider what we have in the case of every powerful galvanic battery, on whatever system arranged. We have a series of simple batteries, each consisting of two plates of different metal placed in dilute acid. Whereas, in the case of a simple battery, however, the two different metals are connected together by wires to let the electric current pass (the current ceasing to pass when the wires are disconnected), in a compound battery, in which (let us say) the metals are zinc and copper, the zinc of one battery is connected with the copper of the next, the zinc of this with the copper of another, and so on, the wire to the copper of the first battery and the wire from the zinc of the last battery being free, and forming what are called the poles of the compound battery--the former the positive pole, the later the negative pole. When these free wires are connected, the current of electricity passes, when they are disconnected the current ceases to pass, unless the break between them is such only that the electricity can, as it were, force its way across the gap. When the wires are connected, so that the current flows, it is as though there were a channel for some fluid which flowed readily and easily along the channel. When the circuit is absolutely broken, it is as though such a channel were dammed completely across. If, however, while the poles are not connected by copper wires or by other freely conducting substances, yet the gap is such as the electricity can pass over, the case may be compared to the partial interruption of a channel at some spot where, though the fluid which passes freely along the channel is not able to move so freely; it can yet force its way along, with much disturbance and resistance. Just as at such a part of the course of a liquid stream--say, a river--we find, instead of the quiet flow observed elsewhere, a great noise and tumult, so, where the current of electricity is not able to pass readily we perceive evidence of resistance in the generation of much heat and light (if the resistance is great enough).

It will be observed that I have spoken in the preceding paragraph of the passage of a current along the wire connecting the two poles of a powerful electric battery, or along any substance connecting those poles which possesses the property of being what is called a good conductor of electricity. But the reader is not to assume that there is such a current, or that it is known to flow either from the positive to the negative pole, or from negative to positive pole; or, again, that, as some have suggested, there are two currents which flow simultaneously in opposite directions. We speak conventionally of the current, and for convenience we speak as though some fluid really made its way (when the circuit is complete) from the positive to the negative pole of the compound battery. But the existence of such a current, or of any current at all, is purely hypothetical. I should be disposed, for my own part, to believe that the motion is of the nature of wave-motion, with no actual transference of matter, at least when the circuit is complete. According to this view, where resistance takes place we might conceive that the waves are converted into rollers or breakers, according to the nature of the resistance--actual transference of matter taking place through the action of these changed waves, just as waves which have traversed the free surface of ocean without carrying onward whatever matter may be floating on the surface, cast such matter ashore when, by the resistance of the shoaling bottom or of rocks, they become converted either into rollers or into breakers.

I may also notice, with regard to good conductors and bad conductors of electricity, that they may be compared to substances respectively transparent and opaque for light-waves, or again, to substances which allow heat to pass freely or the reverse. Just as light-waves fail to illuminate a transparent body, and heat-waves fail to warm a body which allows them free passage, so electricity-waves (if electricity really is undulatory, as I imagine) fail to affect any substance along which they travel freely. But as light-waves illuminate an opaque substance, and heat-waves raise the temperature of a substance which impedes their progress, so waves of electricity, when their course is impeded, produce effects which are indicated to us by the resulting heat and light.

A powerful galvanic battery is capable of producing light of intense brilliancy. For this purpose, instead of taking sparks between the two metallic poles, each of these is connected with a piece of carbon (which is nearly as good a conductor as the metal), and the sparks are taken between these two pieces of carbon, usually set so that the one connected with the negative pole is virtually above the one connected with the positive pole, and at a distance of a tenth of an inch from each other or more, according to the strength of the battery. Across this gap between the carbons an arc of light is seen, which in reality results from a series of electric sparks following each other in rapid succession. This arc, called the voltaic arc, is brilliant, but it is not from this arc that the chief part of the light comes. The ends of the carbon become intensely bright, being raised to a white heat. Both the positive and negative carbons are fiercely heated, but the positive is heated most. As (ordinarily) both carbons are thus heated in the open air, combustion necessarily takes place, though it is to be noticed that the lustre of the carbons is not due to combustion, and would remain undiminished if combustion were prevented. The carbons are thus gradually consumed, the positive nearly twice as fast as the negative. If they are left untouched, this process of combustion soon increases the distance between them till it exceeds that which the electricity can pass over. Then the light disappears, the current ceasing to flow. But by bringing the carbon points near to each other (they must, indeed, be made to touch for an instant), the current is made to flow again, and the light is restored.

The following remarks by M.H. Fontaine (translated by Dr. Higgs) may help to explain the nature of the voltaic arc:--'In truth, the voltaic arc is a portion of the electric circuit possessing the properties of all other parts of the same circuit. The molecules swept away from point to point (that is, from one carbon end to the other) 'constitute between these points a mobile chain, more or less conductive, and more or less heated, according to the intensity of the current and the nature and separation of the electrodes' (that is, the quality and distance apart of the carbon or other substances between which the arc is formed). 'These things happen exactly as if the electrodes were united by a metallic wire or carbon rod of small section' (so as to make the resistance to the current great), 'which is but saying that the light produced by the voltaic arc and that obtained by incandescence arise from the same cause--that is, the heating of a resisting substance interposed in the circuit.'

The intensity of the light from the voltaic arc and the carbon points varies with circumstances, but depends chiefly on the amount of electricity generated by the battery. A fair idea of its brilliancy, as compared with all other lights, will be gained from the following statements:--If we represent the brightness of the sun at noon on a clear day as 1,000, the brightness of lime glowing under the intense heat of the oxy-hydrogen flame is about 7; that of the electric light obtained with a battery of 46 elements (Bunsen's), 235. With a battery of 80 elements the brightness is only 238. (These results were obtained in experiments by Fizeau and Foucault.) The intensity does not therefore increase much with the number of the component elements after a certain number is passed. But it increases greatly with the surface, for the experimenters found that with a battery of 46 elements, each composed of 3, with their zinc and copper respectively united to form one element of triple surface, the brightness became 385, or more than one-third of the midday brightness of the sun (that is, the apparent intrinsic lustre of his disc's surface), and 55 times the brightness of the oxy-hydrogen lime-light.

Another way of obtaining an intense heat and light from the electric current generated by a strong battery is to introduce into the electric circuit a substance of small conducting power, and capable of sustaining an intense heat without disintegration, combustion, or melting. Platinum has been used for this purpose. If the conductive power of copper be represented by 100, that of platinum will be represented by 18 only. Thus the resistance experienced by a current in passing through platinum is relatively so great, that if the current is strong the platinum becomes intensely heated, and shines with a brilliant light. A difficulty arises in using this light practically, from the circumstance that when the strength of the current reaches a certain point, the platinum melts, and the circuit being thus broken, the light immediately goes out.