idea. The first experiments were made by observing black figures traced near the circumference of the disc, which was illuminated solely by the rapidly recurring flashes, and it often happened that the figures, with their details, were seen quite as clearly and sharply as though the disc had been stationary; on the other hand, sometimes the edges seemed blurred, as though the disc had moved through a few degrees during the act of discharge. The result being doubtful, the mode of experimenting was quickly changed; about fifteen narrow radial apertures were made near the circumference of the disc, and the flashes and illuminated clouds were observed through these openings, the disc being made to revolve as before. The distance of the eye from the apparatus was about eight inches, and it was of course adjusted so as to obtain distinct vision of the disc. The result was that sometimes the openings were seen quite unchanged in appearance, but more frequently they were most distinctly elongated into well defined streaks some degrees in length. They were observed often and without dif ficulty, but as farther confirmation I may add that I requested Prof. Joy, who was ignorant of the actual form of the aperture, to state his opinion of their apparent shape while the disc was in rotation. The reply was that they resembled Prince Rupert's drops-a not unfair description of the phenomena in question. Repeated estimates of their size were then made with paper and pencil. Some time afterward I measured the velocity which I could communicate to this disc in the manner above described, by attaching to it a small hollow axis through which the steel pin passed, the disc being then caused to wind up a thread stretched by a small weight. The rate of rotation thus attainable was found to be about twelve revolutions per second, which is a little more than I had anticipated. The average size of the streaks was 9°, corresponding to a duration of of a second. It hence results that the duration of the flashes of lightning on the occasion referred to was in round numbers about of a second, some of them, however, seeming to be confined to smaller limits.

I know of only a single circumstance which might militate against the correctness of the above conclusion, and it is but fair to give it such weight as it may carry. Becquerel has succeeded with some difficulty in observing a faint phosphorescence when an electric discharge is passed through rarefied air, and it is not absolutely impossible that the effects observed by me were due to a cause of this kind.

This point can hereafter readily be decided by observing with a revolving disc, not the distant clouds, but a sheet of white paper, placed so as to receive the light from the electrical flashes. Columbia College, Nov. 10th, 1870.

ART. IV.-On the physical condition of a closed circuit contiguous to a permanent and constant Voltaic current; or, on the electrotonic state;" by ALFRED M. MAYER, Ph.D.

IN 1831, after Faraday had made his brilliant and unequaled discoveries of Voltaic and magnetic induction, he gave, in his first series of experimental researches, a section on a "New electrical State or Condition of Matter;" which he designated as the electro-tonic state. This can, in a few words, be explained as a certain state of electrical tension produced in a closed metallic circuit by the proximity of another circuit, through which circulates an electric current. The latter circuit being broken, this tension evinces itself in producing, during its disappearance, an electric wave in the closed circuit, similar in character, but opposite in direction, to the one produced on forming the contiguous electric current.

Faraday, with his habitual philosophic reserve, hesitating to give a formal enunciation of any hypothesis as to the electrical or molecular condition of the wire during this state, says, (Exp. Res. 71) "this peculiar state appears to be a state of tension, and may be considered as equivalent to a current of electricity, at least equal to that produced either when the condition is induced or destroyed." But in the celebrated Bakerian lecture which he delivered in Jan., 1832, he reluctantly releases his mind from this opinion, and says, (Exp. Res. 231; 242), "The law under which the induced electric current excited in bodies moving relatively to magnets, is made dependent on the intersection of the magnetic curves by the metal being thus rendered more precise and definite, seem now even to apply to the cause in the first section of the former paper; and by rendering a perfect reason for the effects produced, take away any for supposing that peculiar condition which I ventured to call the electro-tonic state. * *** Thus the reasons which induce me to suppose a particular state in the wire have disappeared; and though it still seems to me unlikely that a wire at rest in the neighborhood of another carrying a powerful electric current is entirely indifferent to it, yet I am not aware of any distinct facts which authorize the conclusion that it is in a particular state."

In Dec., 1834, however, we see with what reluctance he gave up his first opinion, for he thus writes (Exp. Res. 1114) in reference to "the influence by induction of an electric current on itself, and on the inductive action of electric currents generally." "Notwithstanding that the effects appear only at the making and breaking of contact, (the current remaining unaffected, seemingly, in the interval), I cannot resist the impression that

AM. JOUR. SCI.-THIRD SERIES, VOL. I, No. 1.-JAN., 1871,

there is some connected and correspondent effect produced by this lateral action of the elements of the electric stream during the time of its continuance. An action of this kind, in fact, is evident in the magnetic relations of the parts of the current. But admitting (as we may do for the moment) the magnetic forces to constitute the power which produces such striking and different results at the commencement and termination of a current, still there appears to be a link in the chain of effects, a wheel in the physical mechanism of the action, as yet unrecog nized." Again, in 1838, (Exp. Res. 1661) he recurs to the idea of the electro-tonic state, in speaking of "the transverse effect of a current;" and in his "Relation of the electric and magnetic forces" (Exp. Res. 1729) he states, "It appears to me possible, therefore, and even probable, that magnetic action may be communicated to a distance by the action of the intervening particles, in a manner having a relation to the way in which the inductive forces of static electricity are transferred to a distance; the intervening particles assuming for the time more or less of a peculiar condition, which, (though with a very imperfect idea) I have several times expressed by the term electro

tonic state.'

As late as 1851, Faraday yet hopes that future research may verify his idea of the electro-tonic state, for in his paper "on the lines of magnetic force," after having shown the relation of the magneto-electric current to the electro-conducting power of the substance in which it is induced, he writes (Exp. Res. 317273), "All the results described are those obtained with moving metals. But mere motion would not generate a relation, which had not a foundation in the existence of some previous state; and therefore the quiescent metals must be in some relation to the active center of force, and that not necessarily dependent on their paramagnetic or diamagnetic condition, because a metal at zero in that respect, would have an electric current generated in it as well as the others. The relation is not as the attractions or repulsions of the metals, and therefore not magnetic in the common sense of the word; but according to some other functions of the power. If such a condition be hereafter verified by experiment, and the idea of an electrotonic state be revived and established, then, such bodies as water, oil, resin, &c., will probably be included in the same state; for the non-conducting condition, which prevents the formation of a current in them, does not militate against the existence of that condition, which is prior to the effect of motion. A piece of copper, which cannot have the current, because it is not in a circuit, and a piece of lac, which cannot, because it is a non-conductor of electricity, may have peculiar but analogous states, when moving across a field of magnetic power."

*

*

*

*

*

In his paper on the physical character of the lines of magnetic force, occurs this remarkable paragraph (Exp. Res. 3269): "The mutual relation of the magnetic lines of force and the electric axis of power has been known ever since the time of Ersted and Ampère. This, with such considerations as I have endeavored to advance, enables us to form a guess or judgment, with a certain degree of probability, respecting the nature of the lines of magnetic force. I incline to the opinion that they have a physical existence correspondent to that of their analogue, the electric lines; and having that notion, am further carried on to consider whether they have a probable dynamic condition, analogous to that of the electric axis to which they are so closely, and, perhaps, inevitably related, in which case the idea of magnetic currents would arise; or whether they consist in a state of tension (of the æther?) round the electric axis, and may therefore be considered as static in their nature. Again and again the idea of an electro-tonic state has been forced on my mind; such a state would coincide and become identified with that which would then constitute the physical lines of magnetic force."

We see from the above extracts (all that refer to this subject) that Faraday never gave a formal statement of his conception of the physical condition constituting the electro-tonic state; but other electricians, including Weber, Neumann and A. De la Rive, have framed hypotheses, more or less probable, to explain this condition. The one most generally received, and indeed widely copied into existing treatises on physics, is that of A. De la Rive. (Traité d'Electricité, t. i, p. 445). I here give this in his own words; and will then describe certain experiments of precision, which I have made to test the truth of his hypothesis. This is the object of making this communication. "Without having recourse to conceptions and calculations as profound as Weber and Neumann's, I think that we can consider induction as the result of the ordinary inductive decomposition of the natural electricity of each particle of the induced conductor, by the already separated electricities of each corresponding particle of the inductor. In order that this shall take place, we must admit that the propagation of the current takes place by a series of decompositions and recompositions of the electricities of the successive molecules, in the same manner as takes place with insulating bodies, (referring to Faraday's theory of inductive action).

"Let A B be a conductor traversed by a current in the direction from A to B; the successive particles of which it is composed have their natural electricity decomposed, the turned towards A where is the positive pole of the apparatus, and the + turned towards B where is the negative pole. The electrici

ties, as soon as they have been separated, combine from particle to particle, thus: the negative of a with the positive of the pole A, the negative of b with the positive of a, and so on to the positive of h which combines with the negative of the pole B.

This recomposition, which is instantaneous, is immediately followed by a new decomposition, and this by a recomposition, and so on. This succession of decomposition and of recomposition is so rapid, that there is always, as experiment shows, an electric tension in each particle of the conductor, so that we can consider that the state in which it is represented in the figure, which we will call state of polarization, is nearly permanent.

"Now let A'B' be a second conductor similar to the first, as near to it as possible, and insulated with silk or wax. At the moment we pass a current in A B, and where consequently we polarize its particles, we produce in A'B' an opposite molecular polarization, the + of each particle being opposite the of each particle of A B and the before the +. It thereby follows that if, at the moment when A B is traversed by a current, the two extremities of A'B' are united by a conductor, such as the wire of a galvanometer, the + of the molecule a' combines, through this conductor, with the of the molecule h', and this produces an instantaneous current directed from A' to B' in the conductor, and from B' to A' in the wire A'B' itself, that is to say in a direction contrary to the inducing current. Also, if instead of being united by a conductor, the extremities A' and B' communicate with the two plates of a condenser, A' will give it a charge of positive electricity, and B' one of negative. As soon as a' has lost its positive electricity and h' its negative, the negative of a' is then disguised by the positive of b', and so on to the negative of g', which is disguised by the positive of h; these electricities do not neutralize each other, because they are retained by the opposite electricities of the particles of AB; but if at the instant that the current ceases to pass in A B, the