the matter with whatever accuracy and precision may be had from the little scientific knowledge within my reach, as I believe that the evidence which such knowledge can allege is sufficiently strong and satisfactory to put common sense," which in this case is common ignorance, out of court.

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In the first place I must express my dissent from his opinion that it is not scientifically accurate to say that we do hear the human voice. There is a philosophy which holds that the testimony of our senses is unreliable as to their objects, and which thereby attempts to divorce science from the common sense of life. If there is inaccuracy in the expression, "hearing the voice," it is equally inaccurate to speak of "seeing a face," " touching a hand," and the conclusion must be at least the modified idealism of Herbert Spencer, that although the relation of my senses as to external objects may be practically useful for ordinary purposes, I must always put in a mental caveat against believing a real correspondence between the sensation in consciousness and the plexus of phenomena which gave rise to them. If Professor Ryan comes to that, I decline to argue further with him. I maintain that our senses do give us accurate knowledge, and that they do report to us accurately as to their objects, and the business of a true philosophy is to accept this fundamental fact and explain it, and not to attempt to impugn its certainty, and thus weaken the foundations of all knowledge.

I think then that we are safe in starting with the assumption that the expression, "hearing the human voice," represents a real objective phenomenon, and if we are to determine whether that phenomenon can be truly predicated in the case of the telephone, we must know what we mean by it as it is ordinarily used.

My description of it is as follows, but it must be borne in mind that I give it in the phraseology of the accepted theory of the vibratory character of sound in relation to which this discussion, in its present stage, must be conducted.

When I say then that I hear the human voice, I mean that a person's vocal organs have moved and given a vibratory motion, which is recognised as sound, to the air particles in immediate contact with them. These being elastic, yield to the pulse which they have received, and recoil, and thus send on the pulse to the next layer or shell of air,

until at last a series of vibrations, constituting a soundwave reaches the membrane of the drum of my ear, which takes up the same vibratory motion, and in some mysterious way passes the sound on to the brain.

Now, in this series of phenomena, constituting what is known as sound, I have to direct attention to a few especial points that seem to me to go to the kernel of this discussion:

1o The energy which is in play is not energy in general, but the special form of it known as sound. 2o That sonorous pulse, or sound energy, passes along the various lines of air particles, by their elasticity, preserving all through its course the same sonorous character until it impinges on the ear. 3o It is the same energy that at first is developed by the sounding body, and at the end affects the membrane of the ear; and finally, I have to add that this description is taken almost word for word from Professor Tyndall's lectures on sound, and is, I think, not only popular and sufficient, but, making due allowance for my poverty of expression, and scientific exposition, scientifically correct according to the received vibratory theory.

I will collate these points with the views of Professor Ryan, not precisely in the order I have given, but as they are suggested by the sequence of his argument, thus to refute him, or at least, to bring out distinctly the substance of our difference.

I will take first, then, his disquisition on identity and similarity of sound, in which he puts forward what seems to me these propositions: 1° That in strictness, identity cannot, in the vibratory theory, be predicated of a sound; and 2o that in the loose and popular language which may be admissible that perfect similarity is sufficient to constitute identity. Lest through misapprehension I may wrong him, I quote his words:

"For my part, I consider the word identical inapplicable in both cases; but as sound is vibration, if identity can be predicated of two sounds, it should depend on the identity of the period and amplitude of vibration, and on the equality of the masses of the vibrating particles-in fact, on mechanical and material similarity."

Therefore, the sound-waves proceeding from the telephone being mechanically similar to those falling upon it, are as much and as little entitled to be regarded as identical with the latter as if they had been produced in the ordinary way, neither more nor less."

On the other side I argued, and still maintain, that no "mere mechanical and material similarity" between the sound communicated to the transmitting instrument of a telephone and that given out by the receiver was of use to prove their identity, unless the latter were shown to be the continuation of the sonorous wave that constituted the existence of the former.

On Professor Ryan's theory a good mimic, a well trained parrot, or any other contrivance that could produce a sound perfectly similar to that of the sound imitated, would be as much and as little entitled to be called identical with it, as a man's own voice heard by different people at the same time or in succession at different distances. It is a strange philosophy that leads to such a conclusion.

To my mind the distinction between identity and similarity is neither "arbitrary nor "unreal," but most obvious. If I strike a tuning fork, its particles give a pulse, a sound-pulse-to the air particles in contact with it-and as long as that sound-pulse passes in unbroken succession from layer to layer of air particles, there is a sound-one sound-identical all through. It is identical with the vibrations of the air particles, that is with the sonorous wave passing in the form of vibrations through these particles of air.

If I strike the same tuning fork in perfectly similər circumstances, and in the same way to-morrow, I will get what I call an exactly similar sound, in amplitude and period of vibrations, &c., but not the same physical thing that constituted the sound of the day before. The two sounds are identical in value, but not in being--just as two sovereigns of the same weight and material are the same in value, but not in physical existence. I think this is plain, and I really do not know why the point has been raised. The exact resemblance which is alleged to exist, but which, as a matter of fact, does not exist between the sounds at both ends of a telephone proves nothing, and I think I am not only right, but evidently so when I contend that those who assert that they are both the sound of the same voice are under the necessity of establishing some more intimate connection between them.

Professor Ryan, at the expense of consistency, supplies that connection and proceeds:

"The preservation of individuality in what is called a soundwave or a series of waves does not warrant us in describing

succeeding vibrations as identical with proceeding. There is no exact conservation of motion, or vibration, or sound. Energy is the only thing which persists and is conserved through all transformations, and for which identity can be claimed at the end of its passage."

Again he writes p. 243:

"To sum up: My contention is that in all cases of communication by speech the hearer is merely cognizant of certain intelligible mechanical disturbances due to energy transmitted to him from the speaker."

Again, same page.

"It (the telephone) certainly conveys sound-waves to the listener not to be distinguished from those received in the ordinary way, and there is no break in the transmission of energy."

The suggestion in all these passages is, that the conservation of "energy" in the telephone is enough to give identity, as far as it is practicable, to the sounds at either end, without having regard to the forms which that energy may assume in the intermediate stage.

But, observe in the description which I have given of the phenomena of speech and hearing, as they ordinarily occur, that the listener is cognizant of more than energy in general passing from the speaker. "Energy in general!" Why, in the words of the old professor commenting on the sign-board, "Smith in general," there is no such thing.

Energy exists, or at least is known to us only in the concrete, and when I hear a voice I am cognizant not merely of energy but of energy differentiated as sound. I may not know what sound is in itself, no more than I know what heat and light and electricity are. But, I know that heat, as such, is not light, nor electricity either, although there may be, and most probably is, some mysterious correlation between all forces, or forms of energy. So, sound is not light, no more than seeing is hearing, and, consequently, when I affirm that I hear a man's voice, I mean that energy, under the special form of sound-articulate sound -has passed from his vocal organs to my ear.

That same description answers all Professor Ryan has written about "String Telephones," "A man shut up in an air-tight box," and all other illustrations, in which he attempts to find analogies for the telephone. In all such

cases, and, in fact, in every known case in which sound travels, it is sonorous in every stage of its course from sounding body to listener. The energy that is called into play is distinguishable as sound, and it preserves that sonorous character all through. There is no instance that I know of a sound in transit ceasing to be sonorous. Why, it seems a contradiction in terms. You might as well talk of an incorporeal body, or an invisible colour, as an inaudible sound. However it passes, whatever the medium, it is always recognisable as sonorous. Intercept it at any stage of its course, and it is audible. Bring your ear to any point along a string telephone, and you get the true sonorous vibration; so, also, with a beam of timber. Cut it and you hear the sound as it travels along; and the same holds good, as far as I know, for every instance of an ascertained phenomenon of sound. A speaking tube merely directs the sound waves. A partition between two rooms receives the sound wave as sonorous, preserves and transmits it as such; but, compare with all these instances in which Professor Ryan thinks he finds analogies for the telephone that instrument itself. Tap the wire of the telephone and you will get an electrical current, which, according to its quantity and intensity, will produce the same effect as any ordinary electrical current. In the whole science of sound and acoustics there is nothing bearing the faintest resemblance to such a phenomenon, and if the question is to be discussed fruitfully it must be with a recognition of this fact. There is no sound that can be detected between the extremes of the telephone; and this fact of itself is sufficient, in my opinion, to destroy the whole reasoning in Professor Ryan's

essay.

He felt the force of this difficulty, and attempts to remove it by what appears to me a very weak and unscientific expedient:

"If we imagine these particles to be merely like tennis-balls we must admit that the transformation of mechanical energy into electrical energy in the telephone wire constitutes apparently an important difference in the method of propagation. It should be remembered, however, that the transmission along the wire is practically instantaneous. The time occupied is much too short to be perceptible on ordinary lines. The inappreciable

interval of time during which the energy of the original soundwave is being transmitted along the wire hardly forms a solution of continuity. The energy is active all the while.”