Essays on the use and limit of the imagination in science

by John Tyndall

In affirming that the growth of the body is mechanical, and that thought, as exercised by us, has its correlative in the physics of the brain, I think the position of the ‘Materialist’ is stated, as far as that position is a tenable one. I think the materialist will be able finally to maintain this position against all attacks; but I do not think, in the present condition of the human mind, that he can pass beyond this position. I do not think he is entitled to say that his molecular groupings and his molecular motions explain everything. In reality they explain nothing. The utmost he can affirm is the association of two classes of phenomena, of whose real bond of union he is in absolute ignorance. The problem of the connexion of body and soul is as insoluble in its modern form as it was in the prescientific ages. Phosphorus is known to enter into the composition of the human brain, and a trenchant German writer has exclaimed, ‘Ohne Phosphor, kein Gedanke.’ That may or may not be the case; but even if we knew it to be the case, the knowledge would not lighten our darkness. On both sides of the zone here assigned to the materialist he is equally helpless. If you ask him whence is this ‘Matter’ of which we have been discoursing, who or what divided it into molecules, who or what impressed upon them this necessity of running into organic forms, he has no answer. Science is mute in reply to these questions. But if the materialist is confounded and science rendered dumb, who else is prepared with a solution? To whom has this arm of the Lord been revealed? Let us lower our heads and acknowledge our ignorance, priest and philosopher, one and all. Perhaps the mystery may resolve itself into knowledge at some future day. The process of things upon this earth has been one of amelioration. It is a long way from the Iguanodon and his contemporaries to the President and Members of the British Association. And whether we regard the improvement from the scientific or from the theological point of view, as the result of progressive development, or as the result of successive exhibitions of creative energy, neither view entitles us to assume that man’s present faculties end the series,—that the process of amelioration stops at him. A time may therefore come when this ultra-scientific region by which we are now enfolded may offer itself to terrestrial, if not to human investigation. Two-thirds of the rays emitted by the sun fail to arouse in the eye the sense of vision. The rays exist, but the visual organ requisite for their translation into light does not exist. And so from this region of darkness and mystery which surrounds us, rays may now be darting which require but the development of the proper intellectual organs to translate them into knowledge as far surpassing ours as ours surpasses that of the wallowing reptiles which once held possession of this planet. Meanwhile the mystery is not without its uses. It certainly may be made a power in the human soul; but it is a power which has feeling, not knowledge, for its base. It may be, and will be, and we hope is turned to account, both in steadying and strengthening the intellect, and in rescuing man from that littleness to which, in the struggle for existence, or for precedence in the world, he is continually prone.

EARLIER THOUGHTS.[8]

A WORK recently published by Mr. Murray contains a sketch of the grounds on which the most advanced scientific thinkers of the present day base their convictions as to the physical character of Light and Heat. The fundamental idea there developed is, that the phenomena of light and heat, like those of sound, are essentially mechanical. Precisely the same reasoning applies to the vibrating ether which produces the one as to the vibrating air which produces the other, and both are dealt with substantially as we should deal with the waves of a liquid or the swing of a pendulum. Reflection on this subject has suggested the thought that the considerations brought forward in the sketch referred to may apply themselves to certain phenomena which are usually considered to lie outside the pale of physics, and thus may indicate new relationships between man regarded as a being of intellect and emotion, and the wondrous material system in the midst of which he dwells.

All our intercourse with the external world consists exclusively in an interchange of motion. From a vibrating, sonorous body, for example, pulses are sent to the ear and stir the auditory nerve to motion. From a luminous body pulses are sent to the eye, and stir the optic nerve to motion. Other pulses of different periods strike upon other nerves, and produce the sensation of heat; but, in all cases, whether it be light, or sound, or ordinary feeling, the excitement of the nerves, regarded more strictly, is the excitement of motion. And if the motion be induced by internal causes instead of external, is it not fair to infer that the effect on consciousness will be the same? Let any nerve, for example, be thrown by morbid action into the precise state of motion which would be communicated to it by the pulses of a heated body, surely that nerve will declare itself hot—the mind will accept the subjective intimation exactly as if it were objective. The retina, as is well known, may be excited by purely mechanical means. A blow on the eye will cause a luminous flash, and the mere pressure of the finger on the external ball will produce a star of light, which Newton compared to the circles on a peacock’s tail. Disease makes people see visions and dream dreams; but, in all such cases, could we examine the organs implicated, we should, on philosophical grounds, expect to find them in that precise molecular condition which the real objects, if present, would superinduce.

The colour of light is determined by the frequency of the ethereal vibrations, as the pitch of sound is determined by the frequency of the aërial ones. The red or purple, for example, of a British maiden’s cheek and lips, the blue, violet, or brown of her eyes, have their strict physical equivalents in the lengths of the waves which issue from them; and these waves are not only as truly mechanical as the waves of the sea, but they are capable of having their mechanical value expressed in numbers. In the work already referred to, a chapter is devoted to the relation which subsists between light and heat and mere mechanical work. In virtue of this relation we can tell the precise amount of work which a given amount of sunshine can perform. Now, the hue of the cheek is caused by the extinction of certain of the solar rays by the colouring matter of the cheek, the residual colour being that seen. Could we interpose the substance to which some English cheeks owe their bloom in the path of a beam passing through a prism, we should probably find the orange and yellow and green of the prismatic spectrum more or less absorbed, the red and a portion of the blue being transmitted. This would give us a purplish blush resembling that of the permanganate of potash, commonly called the mineral chameleon, a solution of which acts upon the spectrum in the manner just described. Inasmuch, then, as we can calculate with perfect exactness the mechanical value of the total light which falls upon the epidermis, a certain fraction of this will express the mechanical value of the cheek’s colour. We do not therefore jest, but speak the words of truth and soberness when we affirm that the rays to which the tinting of any given cheek is due would, if mechanically applied, be competent to move a wheelbarrow through a certain space, or to lift a scuttle of coals to a certain calculable elevation.

But the human face and eyes flush at times with a radiance which might well be taken for a direct spiritual emanation entirely independent of ‘brute matter.’ Let us examine this point a little. Musical instruments, and also the human voice, have a peculiarity as regards their sounds which differs from mere pitch. A clarionet and a violin, for example, may be both pitched to the same note, but a listener who sees neither can at once tell that the qualities of the notes are different. This difference is what the French call timbre, and the Germans, we believe, Klang. So, also, we can distinguish one vowel from another, though all may have the same pitch. The difference here, according to the recent investigations of Helmholtz, is due to the fact that certain incidental notes commingle in each case with the principal one, and produce a composite result. The ‘harmonics’ of a string are known to be due to minor vibrations which superpose themselves upon the principal ones, as small ripples cover parasitically the surfaces of large sea-waves. The notes of the true simple wave and of its parasites are heard at once, and it is the variation of the latter which produces differences in the timbre of a musical instrument or of the human voice.

In speculating on those more subtle phases of expression to which we have above referred, might we not offer the conjecture that they are not due to those waves alone which make the eyes violet or give the cheek its rose, but are a result produced by the compounding of these with incidental waves, which influence the colour as the harmonic waves of sound influence the pure quality of a note? We have often watched with deep interest and sympathy the countenances of some of the praying women in the churches of the Continent. We have seen a penitent kneeling at a distance from the shrine of the Virgin, as if afraid to come nearer. Suddenly a glow has overspread her countenance, strengthening in radiance, till at length her very soul seemed shining through her features. Sure of her acceptance, she has confidently advanced, fallen prostrate immediately in front of the image, and remained therefor a time in silent ecstasy. We have watched the ebbing of the spiritual tide, and remarked the felicitous repose which it left behind. At each new phase of emotion the timbre of this woman’s countenance changed, and

The music breathing from her face

became altered in quality.

The tendency of the above remarks is to show that the most subtle phases of ‘expression’ have at least a proximate mechanical origin. The splendours of the ‘imperial Eleänore’—the ‘languors of her love deep eyes’—are all reducible to the same cause; and not only so, but they actually exist for a time in space, isolated alike from her and her worshipper. Every gleam of those eyes, every flush of her brows, every motion of her lips requires the ether for its transmission, and a certain calculable time to pass from her to him. During this time, the expression which is to stir the soul, to kindle love or quench it, exists in space as a purely mechanical affection of matter; and, for aught we know, a slight steepness in the front of an ethereal billow, a slight curl of its crest, or some other accident of form, may determine whether the recipient of its shock is to be elated with joy or steeped in misery.