One of the inevitable results of these difficulties in manufacturing processes and of deficiency of knowledge, is the production of a large amount of goods of an inferior quality; and useless goods, technically called "wasters," the cost of which has to be laid upon the saleable ones, and thus the price of the latter is enhanced to the consumer. For instance, flint gla.s.s discoloured by iron has sometimes to be sold at a loss for making common enamel; waste window gla.s.s has to be sold as "rockery" for ornamenting gardens, and defective articles of gla.s.s or metal have to be re-melted.
In consequence of this want of new knowledge, manufacturers continue to suffer losses which might be avoided; high prices of useful articles are maintained; defects in their quality are not improved; preventable accidents still continue to happen; the health of workmen continues to suffer; many means of curing diseases remain unknown; medical practice remains full of empiricism, &c., &c.
The great sewage question is apparently in this predicament; we are probably trying to solve it without first discovering the requisite knowledge; inventors, engineers, and consulting chemists have racked their brains, and have not been able to devise a satisfactory {76} remedy, and meanwhile the health of the entire population of this country is suffering.
If we so neglect the fundamental means of ameliorating our condition we deserve to suffer. One would suppose that cholera, contagious diseases, colliery accidents, pollution of air and water, enormous waste of heat from fires, and a mult.i.tude of other evils which depend upon physical and chemical conditions, are of but little importance, that we should so neglect one of the most effectual means of preventing them; and it is perfectly clear that by neglecting to aid research, those who gain so much money and advantage from original science, and render no return, are unwittingly sacrificing national interests upon a large scale to personal benefit.
The practice of some manufacturers using and deriving great profit from new knowledge evolved by research, without recompensing the discoverers, sometimes causes injury to the public welfare by preventing the publication of discoveries which have an immediate practical application. Experience of this kind has constrained me to postpone the publication of a method I have found of readily and quickly converting lumps of white phosphorus into the red variety in a state of powder without protracted heat or grinding.
"What will be the next chapter of British enterprise and invention, and who and where the men to perform the chief part in it? As to the work to be done, there can be no doubt or mystery, for not a day pa.s.ses {77} without loud complaints, indignant remonstrances, fatal oversights, sad mis-calculations, terrible shortcomings, social or material evils to be remedied if possible, whole ma.s.ses of people, indeed whole cla.s.ses to be succoured and lifted out of the slough, and enormous difficulties placed by nature in our way evidently that we may exercise our wit and our virtues in the attempt to overcome them. Here, from all these Isles, there arises a despairing cry from agriculture, as if it had really reached the end of its tether, and had found itself landed in utter helplessness and insolvency--a bad speculation altogether. Here are countless problems, and at the same time countless discoveries, which if they lead to nothing else, prove the inexhaustible nature of our dominion over the elements. Then, for the sea, with its terrible average of wreck and total loss running on without intermission and with but rare abatement, who shall say there is here no work for the discoverer and inventor who will give his heart and soul and mind to it?"
It is indeed high time, that by means of discoveries which will enable us to predict with certainty the nature of coming seasons, we shall be better enabled to cope with adversities in agriculture; also, that the numerous wrecks, and the thousands of lives lost with them every year on our coasts, should be diminished. But these desirable results cannot be effected by invention based upon insufficient knowledge; invention must be preceded by general as well as special research, because the former often discloses important {78} truths which we cannot predict. Our present electric lights in light-houses and on large ocean steamers, had their origin, not in direct inventions or special researches for the purpose, but in abstract researches on apparently remote subjects.
It is nothing less than a national crime that proper provision has not yet been made for investigating scientifically the causes of famine and pestilence, also physiology and pathology, and the discovery of the laws which regulate diseases and epidemics. What can be more painful to behold than a mother and father deprived of a whole family of five or six children in rapid succession by scarlatina or other contagious disease, and both the parents and medical men utterly unable to save them; and this is a common occurrence. Persons who are ignorant of science look with an abject feeling of helplessness upon great national calamities, and even upon private afflictions, such as a local epidemic, as if there was absolutely no remedy, whilst scientific men believe that by extension of knowledge, such evils might be largely avoided or prevented.
Many persons however, actuated by the very kindest of motives, but insufficiently acquainted with the necessity, conditions, results, and advantages of experiments, unwittingly obstruct the discovery of new knowledge in physiology and pathology, by attempting to prevent experiments being made upon animals.
We should not strain at a gnat and swallow a camel. Nearly every step in life involves a choice {79} between two alternatives, and this is the case with experiments upon living creatures, either such experiments must be made, or the wholesale slaughter of men and other animals, by pestilences, epidemics, small-pox, foot and mouth disease, &c., must continue. Many of the properties of living bodies, like those of dead ones, can only be ascertained by means of experiments, no other course is possible; and the knowledge so obtained enables us not only to prolong the lives but also to alleviate the sufferings of all kinds of living creatures. Nearly all our medical and surgical knowledge has been obtained by observation and study, either of the results of experiments made by ourselves, or by the course of nature for us; and the former is often attended by immeasurably less pain and expence than the latter. No one who has ever made in a proper manner new experiments, would venture to a.s.sert that valuable knowledge is not gained by them; and this statement is as correct of experiments in physiology as in all the other sciences.
The total amount of pain inflicted upon animals by vivisection experiments in this country is infinitesimally small--because, firstly, the proportion of experimentalists in so-called "vivisection," does not amount to one person in one million of our inhabitants:--secondly, students cannot be induced to enter upon scientific research in physiology, because such labour is unrewarded, either by enabling them to obtain certificates, degrees, or money. Whatever pain also, {80} is inflicted in such experiments, is by men of the highest eminence in physiology, and therefore by the most competent persons.
Experimental research is an occupation requiring an exceptional kind of ability and experience; and persons who have never made experiments, nor studied their relation to human welfare, are largely incompetent to determine when and how they should be made, the real effects of them, or the value of the knowledge they afford. To persons inexperienced in scientific research, many experiments appear useless, which have great practical value, either immediately or at a later period. Our greatest curse is ignorance; and knowledge, by enabling us to avoid the fatal effects of pestilences, and epidemics, is as necessary as food to mankind.
The "Anti-vivisection" movement however is but one of the phases of the ever-existing conflict between the advancing and r.e.t.a.r.ding sections of mankind.
Greater sympathy with suffering accompanies greater civilization. The increased humanity of the present age over that of previous ones, is largely due to the discovery and extension of new scientific knowledge.
Science, by showing more clearly to man his true position in nature and in relation to his fellow-men and other animals, has rendered more evident the concrete fact, that the happiness of each depends upon the happiness of all, and the happiness and welfare of all upon that of each individual. It has also operated in a more apparent, though less {81} important way, by inculcating better systems of hygiene, improved sanitary arrangements, &c, &c. It is not to the zeal of "anti-vivisectionists," but to the well-directed labours of experimental medical men, that mankind are indebted for the discovery and invention of nearly every known method of preventing and alleviating animal suffering and of prolonging human life.
This statement is true of vaccination, the use of chloroform in general surgery, dentistry, and midwifery, of carbolic acid spray in surgical operations; the abolition of the practice of searing amputated limbs with a red-hot iron; and many other improvements. Ferrier"s comparatively recent vivisection experiments have already enabled medical men to treat more successfully those formidable diseases, epilepsy and abcess of the brain.
What this nation badly requires, is not less experimental research, but more. When famines result from insufficiency of Solar heat, instead of investigating the conditions of the Sun"s surface to enable us to predict their occurrence and provide accordingly, we allow them to come upon us in our unprepared state and produce their fearful effects. When contagious disease overtakes us, what do we do? Instead of previously employing and paying scientific investigators to make experiments in physiological and chemical science, to enable us to combat it successfully, we vainly attempt to apply our present stock of chemical and physiological knowledge to ward off the difficulty. When high price of fuel intervenes, instead {82} of previously giving discoverers the means of finding new principles relating to heat, and to chemical, and electrical action, we ineffectually endeavour by means of invention, to economise fuel. These are the pottering, short-sighted, and ignorant ways in which "the great English nation"
temporises with great evils, and permits national welfare to be sacrificed to private gain, instead of employing for the discovery of new knowledge some of that superfluous wealth which in many instances is a curse to its possessors.
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CHAPTER II.
THE SCIENTIFIC BASIS OF MENTAL AND MORAL PROGRESS.[12]
It is not highly necessary after what has been already said in these pages, to adduce much evidence to show that scientific discoveries, either directly or through the medium of the inventions based upon them, have been a great cause of mental and moral progress. As however there are many persons who do not perceive the dependence of such progress, and especially of moral advance, upon science, a few of the chief relations of those subjects to each other may be pointed out.
The dependence of mental progress upon science may be rendered manifest in several ways:--1st. By showing that new scientific knowledge is continually extending and modifying our views of existing things. 2nd. That inventions based upon scientific discoveries have aided and extended our mental powers:--3rd. That mental phenomena may be made the subject of experiment, observation, a.n.a.lysis, and {84} inference:--4th. That the criteria of truth, and the mental powers and processes employed for discovering and detecting truth, are the same in mental as in physical science, and, 5th.
That mental action is subject to the great principles and laws of science.
And moral progress may be proved to have a scientific basis:--1st. By shewing that moral actions are a cla.s.s of mental actions, and therefore subject to the same fundamental laws and influences:--2nd. That the discovery of new scientific knowledge, and the use of inventions based upon it, often conduce to morality:--3rd. That moral phenomena may be made the subject of experiment, observation, a.n.a.lysis, and inference:--4th. That the criteria of truth, and the mental faculties and processes employed, in discovering truth, are the same in moral as in physical science:--5th. That the fundamental rules of morality are subject to the great principles of science:--6th. That moral improvement follows in the wake of scientific advance:--and 7th. By showing the moral influence of experimental research in imparting "the scientific spirit;" promoting a love of truth; dispelling ignorance and superst.i.tion; detecting error; imparting certainty and accuracy to our knowledge; inculcating obedience to law; producing uniformity of belief; aiding economy and cleanliness, promoting humanity, &c, &c. Each of these will be treated with extreme brevity.
MENTAL PROGRESS.
The chief object of this chapter is only to shew {85} that mental action is largely consistent with the great principles of science; not that in our present state of knowledge, mental phenomena can be entirely explained by them, or that mental actions involve nothing more than physical and chemical processes.
That mental progress is advanced by scientific discovery is a common circ.u.mstance. Our ideas of facts, our knowledge of general principles, our views of man, of nature, and of the Universe; and even our modes of thought, have been gradually and profoundly changed by the new knowledge acquired by means of scientific research. This truth is capable of being most extensively ill.u.s.trated by a mult.i.tude of facts in the whole of the sciences, and in the arts, manufactures, and other subjects dependent upon science. For example, in astronomy, great changes, produced by the results of scientific discovery have taken place in our ideas respecting the magnitude of s.p.a.ce and of the Heavenly bodies, the const.i.tution, form, and motion of the Earth, the functions of the Sun and Moon, the distances of the Sun and fixed Stars, the nature of eclipses and comets; and a great many other matters. In terrestrial physics, the mental advances have been equally great in our ideas respecting the causes of tides and of winds, the pressure of the atmosphere, the existence and course of the Gulf Stream, the physical conditions of the Equator and Poles, the conditions upon which day and night, summer and winter depend, the depth of the ocean, the height of the atmosphere, the cause of rainbows, of {86} rain, hail, snow, mist and dew, of thunder and lightning, the composition of air, water, mineral, and organic substances, and other most numerous and varied phenomena. In the subjects of heat, light, electricity, magnetism, chemistry, vegetable and animal physiology, psychology and morality, and the more concrete subjects depending upon them, such as politics, trade, commerce, government, &c., our ideas have equally advanced, in consequence of scientific research; and to fully describe the mental progress resulting from discovery in nearly all branches of human knowledge would require a series of books to be written on the History of all the Sciences.
Other causes also, which I need hardly mention, besides scientific discovery, have of course contributed to the mental progress of mankind. We arrive at true ideas, not only by the more certain and systematic process employed in scientific research, but largely also by the uncertain method of trusting to instinct and habit, by adopting dogmatic opinions, and by the semi-scientific plan of following empirical rules.
Dogma and empiricism, in nearly all subjects, has rendered immense service to mankind. Contemporaneously with the progress produced by new knowledge, the mental condition of man has been maintained and prevented from receding, by the combined influence of hereditary mental proclivity, acquired habit, promulgation of dogmatic opinions and empirical rules, and by previously known verified truth. Religious {87} belief has thus been the forerunner of Science. Dogma and empiricism are indispensable agents of civilization; they cannot be dispensed with by the great ma.s.s of mankind, who have not the time at command, nor possess the other means, necessary for acquiring verified knowledge. They afford rough and ready guides and useful "rule of thumb" methods, though less certain and less accurate than those afforded by verified and definite science.
That various inventions, based upon scientific discoveries, have greatly aided and extended our mental powers is quite certain. The discovery of the properties of a mixture of solution of nutgalls and green vitriol, has, through the invention of ink, exercised an immense influence in promoting the mental developement of mankind; and the discovery of the properties of esparto gra.s.s and other materials for making paper has contributed to this result. Every discovery also resulting in inventions which facilitated the transmission of intelligence has had a similar effect. Amongst these are magnetism, which, in the mariner"s compa.s.s greatly a.s.sisted navigation and the conveyance of letters by sea; and the steam engine which facilitated the transmission of letters by land and by water; the electric telegraph, the telephone, and other contrivances for transmitting ideas, have also greatly promoted mental advance. The steam engine, by largely abolishing physical drudgery, gave time for study and mental and moral improvement. It has been said that "it is impossible to lay down a {88} railway without creating an improved intellectual influence. It is probable that Watt and Stephenson will eventually modify the opinions of mankind, almost as profoundly as Luther and Voltaire." Photography has exercised an immense intellectual influence of an improved kind, by making common to all mankind views of the beautiful scenery of all parts of our globe, and portraits of individuals of all nations and of all cla.s.ses of society. Processes of printing from electrotype plates, pictures and letter-press, upon the paper wrappers used by grocers and other tradesmen, have also carried into the homes of millions of poor persons truthful ideas and an improved intellectual influence. The invention of steel pens, of which a thousand millions are made yearly in Birmingham alone, must also have considerably aided intellectual progress. The various calculating machines used by merchants, the copying presses, papyrographs, and the numerous inventions for copying and multiplying letters and circulars and for domestic printing, have saved intellectual toil, and promoted the diffusion of intelligence. These are only a few of the numerous ways in which inventions based upon scientific discoveries, have resulted in mental progress.
Less perhaps has been done in the way of actual definite scientific experiments upon mental actions and processes than in almost any other department of science, and this is partly accounted for by the fact that the other sciences require to be largely advanced before we can use them to examine mental action, {89} and partly also because (as occasionally happens) the latter has been a neglected subject of research. During the past few years however, various experimental investigations have been made, especially by Donders in Holland, and Mosso in Turin, for the purpose of elucidating the physical conditions of mental action; and it has been found that instead of an act of thought being instantaneous, as was formerly believed, it requires a variable time.[13] Numerous desultory experiments made upon dreamers, and with drugs, alcohol, &c., upon persons in the waking state, also prove that mental phenomena are amenable to scientific research. F. Galton has even proposed experiments and methods for measuring the mental faculties of different persons.[14] The effects of exciting different parts of the brain of animals by means of electric currents, and the localization of the functions of the brain effected by the experiments of Ferrier, Hirtzig and others, also tend to throw further light upon mental phenomena. The fact alone that mental actions and conditions may be made the subject of experiment, and consequently of observation, comparison, a.n.a.lysis and inference, proves that they may be rendered sources of new facts and principles, and are therefore within the domain of science. As the dependence of mental phenomena upon physical conditions has been clearly demonstrated, an extensive reduction of them to scientific laws is only a question of time and labour.
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The principles of nature and the modes of mental action are the same for all men. It necessarily follows from the essential nature of truth and the invariability of the chief methods of detecting it, that the criteria of truth in mental science, and the mental powers and processes by which truth is arrived at and detected in that science, are essentially the same as in the physiological, chemical, and physical ones. In each of these subjects, we first, either with or without the aid of experiment, make observations, record facts, compare them, and draw conclusions from our comparisons; we also group the facts, and the conclusions, in every possible way, and then draw other conclusions; we also a.n.a.lyse, combine, and permutate the various truths arrived at, and cross examine the evidence in every possible manner in order to extract from it the greatest amount of new knowledge. And in each case we employ as the criteria of truth, the test of consistency with the whole of the evidence bearing upon the case, and especially with the great principles of science. We determine what is true, chiefly by comparison with those principles, because they are the most firmly established true ones and the most universal. There is no royal road to truth, and no special mental faculty for detecting it in any subject; and it is in consequence of our mental faculties being so very finite that we have no easier way of arriving at truth.
No dogmatic teaching can ever, except by accident, fully explain to man the true nature of mind; and {91} only in proportion as man becomes enlightened by extension of new scientific knowledge, especially in physiology, will he be able to view himself in a true aspect apart from his consciousness.
Science penetrates deeper than metaphysical speculation, into the nature of mental action, chiefly because metaphysics deals only with old ideas, whilst science furnishes us with new experience and therefore with new conceptions and wider evidence.
Fallacies are very prevalent, every subject of human study is liable to a very large cla.s.s of errors arising from the extremely imperfect state of our knowledge, and in very few subjects is our ignorance as great as in that of mental and moral phenomena. Every different subject of study also, has, in consequence of its special peculiarities, its own peculiar cla.s.s of fallacies, into which the student of it is likely to be led, unless he is previously guarded against them. In accordance with this truth, the study of man"s nature, especially the mental and moral portions, is particularly liable to a cla.s.s of errors arising from the circ.u.mstance, that the phenomena to be observed and the observing power are intimately connected together, each influencing and disturbing the other. The obstacles to our arriving at truth in the study of mental and moral actions, are greater and more frequent, the more nearly and intimately related the phenomena to be observed and contemplated, are to the observing and contemplating faculty, or rather to the contemplative action. When the two mental {92} actions are extremely intimate, as when attention is directed to the action of will (which is itself a conscious act of attention) undisturbed thought becomes very difficult; and when further, the contemplative faculty attempts to contemplate itself, as when consciousness attempts to observe consciousness, in order to define it, the attempt results in almost complete failure, probably because the two actions (observing and being observed) being opposite in kind, cannot coexist at the same time in the same structure. Knowledge of the exact nature of consciousness therefore, will probably only be arrived at by indirect means, when physiological and other knowledge is sufficiently advanced.
Consciousness, when uncorrected by sufficient knowledge and inference, is a great source of error. That which we feel, we think exists whether it does or not, until the subject is correctly explained to us. The incessant and irresistible obtrusion of consciousness exercises dominion over every mind, even of our greatest thinkers, and causes disturbance and interruption in nearly every train of thought. It is largely the cause of some of our most general ideas and emotions and insensibly influences our views of man and nature. It produces true impressions as well as erroneous ones. It is a cause of the feeling that an occult spirit exists within us independent of our material structure. Combined with the almost equally persistent impression of the uniformity of nature, it largely produces the idea that the spirit within us, {93} will live and be active for ever. And by uniting with the frequent impressions of failure of our efforts and desire for more perfect enjoyment, it largely originates the idea of everlasting happiness.
It is in accordance with modern scientific knowledge, to view the mind, not as a collection of distinct faculties, but rather as a single kind of power, like each of the physical forces, having several different modes of action; and as that which perceives, thinks, and wills. Its oneness is shewn by its inability to be simultaneously occupied by several diverse feelings, thoughts, or volitions, and by our incapacity to think of many varied ideas at once; the more ideas also or objects we attempt to perceive at once, the less we realize of each. In proportion as the mind is engaged upon one idea, so is it also unable to be occupied with another. Strong feelings exclude intellectual action. The mind can only execute several actions at a time, provided they have been rendered more or less automatic by habit, &c., but as all mental acts are in different degrees imperfectly automatic, and require more or less attention, and each individual mind is limited in its power, every such act withdraws a portion of attention from the more engrossing ideas. Power of mind and power of maintaining attention are nearly synonymous.
The recognised fundamental elements of mind are Receptivity and Perception of impression: Retentiveness of impression: Perception of agreement (or similarity) of impression: and Perception of difference {94} of impression.
All purely mental acts appear to be resolvable into these.
Many persons still entertain the idea that mental actions are largely independent of the natural conditions to which physiological, chemical, and physical phenomena are subject. The unscientific mind is readily beguiled by easy schemes of mental action, or simple systems of mental and moral philosophy, unaware that great abstract truths often require deep thought to discover them, or even to perceive them when discovered and published.
"A false notion, which is clear and precise, will always meet a greater number of adherents in the world than a true principle which is obscure."
It is not until unscientific persons have become used to advanced scientific ideas and nomenclature, and knowledge as so far progressed as to enable thinking men to ill.u.s.trate those ideas freely in familiar language, that great abstract truths are believed by the public. The ordinary and simple theory of the operations of the human mind is, that they often arise without any cause, and are frequently not obedient to ordinary influences, and this idea is still entertained and promulgated even by some of our most popular ministers of truth. It is therefore necessary in order to further prove that new scientific knowledge is really a basis of mental progress, to point out a few of the chief ways in which mental action essentially depends on scientific principles, and to adduce a few instances in which other substances than brain exhibit essentially similar phenomena. To {95} shew this however in a more satisfactory manner would require a large treatise to be written upon the subject.
The human brain and mind are evidently subject to the ordinary laws of matter and energy. Receptivity and retentiveness of impression is not only a property of brain, but of all solid matter without exception. Moser"s pictures, and Chinese mirrors, the impressions on each being reproducible by warm breath, are examples of this. And as these two properties are fundamental elements of mind, they must be present in and essential to, every mental action.
All phenomena require time and all matter occupies s.p.a.ce; thought and brain are no exception to this. Whilst all persons say "I must have time to think," many believe that thought is instantaneous. Time is a necessary condition of all thought, and therefore of all comparison, inference, imagination, and mental a.n.a.lysis; it takes time even to form an idea, or draw an inference from it, and the two cannot be formed simultaneously.
Professor Donders, of Utrecht, has invented what he terms a Noematachograph for registering the amount of time occupied in mental processes, and by the aid of that instrument has ascertained that the time required by a man of middle age to perform a single act of simple thought is about one twenty-fifth part of a second. It has also been ascertained that the time required is longer in some persons than in others; and longer if the {96} subject of thought is one with which the thinker is not familiar. Mosso, by means of an instrument which he calls a Plethysmograph, has shewn, that during mental action, either in the waking state, or in dreaming, there is a greater amount of blood determined to the brain, and more during difficult than during easy mental action. These are instances of scientific research casting a light upon mental processes.
Coexistence of matter and energy is another great truth which appears to be applicable to all nature; wherever there is matter, there is either active or stored up power; and as particular forms of energy are in some cases most exhibited by particular kinds of substance, (as magnetism by iron), so mind is a.s.sociated with living brain. As also we never see the physical powers exhibited except by material substance, so have we never yet observed mental action in a s.p.a.ce devoid of material. The most perfect vacuum yet produced contains many millions of particles of substance in each cubic inch. Of all the countless number of scientific phenomena observed since men have been able to reliably investigate, not one has afforded us conclusive evidence of mental action entirely independent of these conditions. In accordance also with the usual truth in science, that complicated action requires complex structures; mind, being the most intricate action, is manifested by the most complicated body.
Mind, like each of the physical forces may be {97} viewed as a mode of energy; it is essentially dynamic; activity or change, within or without us, appears to be the original source of all our mental impressions, and the cause of their re-excitement in an act of memory. A man"s mind, being continually excited by circ.u.mstances, must be active whether he will or no, and if it does not possess sufficient truthful ideas entirely to occupy it, it must be more or less occupied with erroneous ones. "We can neither feel, nor know, without a transition or change of state--and every cognition, must be viewed as in relation to some other feeling, or cognition," (Bain.
Mental and Moral Science, p. 83); _i.e._ the mental effect of impressions upon us depends upon our immediately previous mental state; consciousness and perception appear to be based upon cerebral change or activity; after strong excitement of consciousness an increased amount of acid products is found in the secretions. "It is a general law of the mental const.i.tution, more or less recognised by inquirers into the human mind, that change of impression is essential to consciousness in every form," (Bain. Emotions and Will, 3rd edi. p. 550). A sufficient degree also of such change is a necessary condition of conscious perception; it is the stronger or more rapid only of mental changes that excite our consciousness.
We perceive nearly all things by means of a difference of impression which they make upon us; by contrast. That which makes no such difference of impression, such as the great uniformities of time and {98} s.p.a.ce, makes no immediate impression upon us. We only know of the existence of those uniformities by inference from our perceptions of sequences or of relative difference. Although the Earth moves at the rate of 62,000 miles an hour in its...o...b..t, consciousness does not perceive it. If also there was no error, we should be less immediately able to discern truth, without pain we should lose much of the enjoyment of pleasure. Without the contrast of imperfection we could not directly appreciate perfection.
This principle of "relativity," or of change of impression, operates both in the phenomena of dead and living matter and in those of mind; the selenium in a photophone is kept in a state of motion or activity, not by a beam of uniform light, but only by one which changes; electrical action is excited by a relative difference of friction, of temperature, of chemical action, &c.; chemical action also often results from a relative difference of property of two bodies. That the most inscrutable phenomenon of mind, viz., consciousness, is largely dependent upon relative physical and chemical conditions, is proved by the powerful influence which alcohol, chloroform, opium, haschish, and other substances, have in exciting or depressing it. These facts prove that excitement of consciousness or mental action depends upon precisely the same general condition, viz.: change of impression, as the excitement of some of the physical forces; and that mind possesses a similar property to the physical forces of being changed by inequality of impression. {99} Whilst copious evidence is available to shew that the mind is excitable by physical causes, no more conclusive proof exists that a mental impression arises without a natural cause, than that a physical one, such as a photographic impression, arises in that way.
Abundant evidence of non-creation of ideas out of nothing might be adduced; even imagination and invention are subject to this limit, because an unlimited number of new conceptions cannot be formed from a limited number of previous ideas.
The dependence of the mind (like any other mode of energy) upon physical conditions, is further proved by the fact that the mental and moral states of a man are largely governed by sensation; if the latter is unhealthy it makes the mind so, and it makes some difference what the part of the body is in which the sensation exists; most commonly it is the viscera. The mind is also intimately dependent upon the physical condition of the brain, and is largely affected by the quant.i.ty and quality of the blood in that organ.
The most fundamental principle which pervades every one of the sciences, and agrees with the actions of every natural form of energy without exception, including mind, is, that of consistency or non-contradiction. No machine or scientific apparatus of any kind can perform two contradictory acts at the same time. It is both a physiological and psychological fact, that we cannot experience two contradictory sensations, nor perceive two contradictory ideas at the {100} same instant. We can neither feel, perceive, nor observe, one thing, whilst we are feeling, perceiving, or observing, one of a contradictory nature; nor can we perform any two contradictory acts of comparison, inference, imagination, or volition, simultaneously. As also two mental actions are often not exactly alike, or entirely harmonious, they must so far as they are really contradictory, be mutually exclusive; and one of them must partly prevent the other, the strongest one prevailing, and this general truth is commonly though not explicitly, recognised in the maxim, that to do anything well, we must do only one thing at a time. In accordance with the universal truth, that contradictions cannot co-exist, it is well-known that one disease frequently expels another from our frame, and the action of counter-irritants is based upon the same principle. The fort.i.tude of martyrs may probably be explained by this power of one set of ideas and feelings to exclude another, and the facts of mental physiology afford plenty of other examples.