From- the American Journal of Science and Arts, No. 1, Vol. 38. LETTER TO PROF. FARADAY, tJTofy'^ THEORETICAL OPINIONS BY R. HANRE, M. D., Professor of Chemistry in the University of Pennsylvania.* Dear Sir,—I have been indebted to your kindness for several pamphlets comprising your researches in electricity, which I have perused with the greatest degree of interest. You must be too well aware of the height at which you stand, in the estimation of men of science, to doubt that I enter- tain with diffidence, any opinion in opposition to yours. I may say of you as in a former instance of Berzelius, that you occupy an elevation inaccessible to unjustifiable criticism. Under these circumstances, I hope that I may, from you, experience the can- dor and kindness which were displayed by the great Swedish chemist in his reply to my strictures on his nomenclature. I am unable to reconcile the language which you hold in para- graph 1615, with the fundamental position taken in 1155. Agree- ably to the latter, you believe ordinary induction to be the action of contiguous particles, consisting of a species of polarity, instead * To the Editors of the American Journal of Science and Arts,— Gentlemen : I avail myself of the medium of your Journal to address to the celebrated Faraday, a letter on the subject of certain hypothetical inferences which he has made from his late ingenious experimental researches. R. H. 2 A letter to Prof. Faraday. of being an action of either particles or masses at " sensible dis- tances." Agreeably to the former, you conceive that "assuming that a perfect vacuum was to intervene in the course of the line of inductive action, it does not follow from this theory that the line of particles on opposite sides of such a vacuum would not act upon each other." Again, supposing " it possible for a positively electrified particle to be in the centre of a vacuum an inch in di- ameter, nothing in my present view forbids that the particle should act at a distance of half an inch on all the particles forming the disk of the inner superficies of the bounding sphere." Laying these quotations before you for reconsideration, I beg leave to inquire how a positively excited particle, situated as above described, can react " inductrically" with any particles in the super- ficies of the surrounding sphere, if this species of reaction require that the particles between which it takes place be contiguous. Moreover if induction be not "an action either of particles or masses at sensible distances," how can a particle situated as above described, " act at the distance of half an inch on all the particles forming the disk of the inner superficies of the bounding sphere ?" What is a sensible distance, if half an inch is not ? How can the force thus exercised obey the " well known law of the squares of the distances," if as you state (1375) the rare- faction of the air does not alter the intensity of the inductive ac- tion ? In proportion as the air is rarefied, do not its particles be- come more remote ? Can the ponderable particles of a gas be deemed contiguous in the true sense of this word, under any circumstances ? And it may be well here to observe, that admitting induction to arise from an affection of intervening ponderable atoms, it is difficult to con- ceive that the intensity of this affection will be inversely as their number as alleged by you. No such law holds good in the com- munication of heat. The air in contact with a surface at a con- stant elevation of temperature, such for instance as might be supported by boiling water, would not become hotter by being rarefied, and consequently could not become more efficacious in the conduction of heat from the heated surface to a colder one in its vicinity. As soon as I commenced the perusal of your researches on this subject, it occurred to me that the passage of electricity through a vacuum, or a highly rarefied medium, as demonstrated by vari- A letter to Prof. Faraday. 3 ous experiments, and especially those of Davy, was inconsistent with the idea that ponderable matter could be a necessary agent in the process of electrical induction. I therefore inferred that your efforts would be primarily directed to a re-examination of that question. If induction, in acting through a vacuum, be propagated in right lines, may not the curvilinear direction which it pursues, when passing through, " dialectics," be ascribed to the modifying influence which they exert ? If, as you concede, electrified particles on opposite sides of a vacuum can act upon each other, wherefore is the received theory of the mode in which the excited surface of a Leyden jar induces in the opposite surface, a contrary state, objectionable ? As the theory which you have proposed, gives great importance to the idea of polarity, I regret that you have not defined the meaning which you attach to this word. As you designate that to which you refer, as a " species of polarity," it is presumable that you have conceived of several kinds with which ponderable atoms may be endowed. I find it difficult to conceive of any kind which may be capable of as many degrees of intensity as the known phenomena of electricity require ; especially according to your opinion that the only difference between the fluid evolved by galvanic apparatus and that evolved by friction, is due to op- posite extremes in quantity and intensity ; the intensity of elec- trical excitement producible by the one, being almost infinitely greater than that which can be produced by the other. What state of the poles can constitute quantity—what other state inten- sity, the same matter being capable of either electricity, as is well known to be the fact ? Would it not be well to consider how, consistently with any conceivable polarization, and without the assistance of some imponderable matter, any great difference of intensity in inductive power, can be created ? When by friction the surface is polarized so that particles are brought into a state of constraint from which they endeavor to return to their natural state, if nothing be superadded to them, it must be supposed that they have poles capable of existing in two different positions. In one of these positions, dissimilar poles co- inciding, are neutralized; while in the other position, they are more remote, and consequently capable of acting upon other mat- ter. 4 A letter to Prof. Faraday, But I am unable to imagine any change which can admit of gradations of intensity, increasing with remoteness. I cannot figure to myself any reaction which increase of distance would not lessen. Much less can I conceive that such extremes of in- tensity, can be thus created, as those of which you consider the existence as demonstrated. It may be suggested that the change of polarity produced in particles by electrical inductions, may arise from the forced approximation of reciprocally repellent poles, so that the intensity of the inductive force, and of their effort to return to their previous situation, may be susceptible of the gra- dation which your electrical doctrines require. But could the existence of such a repellent force be consistent with the mutual cohesion which appears almost universally to be a property of pon- derable particles ? I am aware that, agreeably to the ingenious hy- pothesis of Mossotti, repulsion is an inherent property of the parti- cles which we call ponderable; but then he assumes the existence of an imponderable fluid to account for cohesion; and for the necessity of such a fluid to account for induction it is my ultimate object to. contend. I would suggest that it can hardly be expe- dient to ascribe the phenomena of electricity to the polarization of ponderable particles, unless it can be shown that if admitted, it would be competent to produce all the known varieties of elec- tric excitement, whether as to its nature or energy. If I comprehend your theory, the opposite electrical state in- duced on one side of a coated pane, when the other is directly electrified, arises from an affection of the intervening vitreous particles, by which a certain polar state caused on one side of the pane, induces an opposite state on the other side. Each vit- reous particle having its poles severally in opposite states, they are arranged as magnetized iron filings in lines ; so that alternately opposite poles are presented in such a manner that all of one kind are exposed at one surface, and all of the other kind at the other surface. Agreeably to this or any other imaginable view of the subject, I cannot avoid considering it inevitable that each particle must have at least two poles. It seems to me that the idea of polarity requires that there shall be in any body possessing it, two opposite poles. Hence you correctly allege that agreeably to your views it is impossible to charge a portion of matter with one electric force without the other. (See par. 1177.) But if all this be true, how can there be a " positively excited particle ?" A letter to Prof Faraday. 5 (See par. 1616.) Must not every particle be excited negatively, if it be excited positively? Must-it not have a negative, as well as a positive pole ? I cannot agree with you in the idea that consistently with the theory which ascribes the phenomena of electricity to one fluid, there can ever be an isolated existence either of the positive or negative state. Agreeably to this theory, any excited space, whether minus or plus, must have an adjoining space relatively in a different state. Between the' phenomena of positive and negative excitement there will be no other distinction than that arising from the direction in which the fluid will endeavor to move. If the excited space be positive, it must strive to flow outward ; if negative, it will strive to flow inward. When suffi- ciently intense, the direction will be shown by the greater length of the spark, when passing from a small ball to a large one. It is always longer when the small ball is positive, and the large one negative, than when their positions are reversed.* But for any current it is no less necessary that the pressure should be on one side comparatively minus, than that on the other side, it should be comparatively plus ; and this state of the forces must exist whether the current originates from a hiatus before, or from pressure behind. One current cannot differ essen- tially from another, however they may be produced. In paragraph 1330, I have been struck with the following query, " What then is to separate the principle of these extremes, perfect conduction and perfect insulation, from each other ; since the moment we leave the smallest degree of perfection at either extremity, we involve the element of perfection at the opposite ends ?" Might not this query be made with as much reason in the case of motion and rest, between the extremes of which there is an infinity of gradations ? If we are not to confound motion with rest, because in proportion as the former is retarded, it differs less from the latter; wherefore should we confound insulation with conduction, because in proportion as the one is less efficient it becomes less remote from the other ? In any case of the intermixture of opposite qualities, may it not be said in the language which you employ " the moment we * See my Essay on the causes of the diversity in the length of the sparks, erro- neously distinguished as positive and negative, in vol. v, American Philosophical Transactions. 6 A letter to Prof. Faraday. leave the element of perfection at one extremity, we involve the element of perfection at the opposite." Might it not be said of light and darkness, or of opaqueness and translucency; in which case to resort to your language again, it might be added " espe cially as we have not in nature, a case of perfection at one ex- tremity or the other." But if there be not in nature, any two bodies of which one possesses the property of perfectly resisting the passage of electricity, while the other is endowed with the faculty of permitting its passage without any resistance ; does this affect the propriety of considering the qualities of insulation and conduction in the abstract, as perfectly distinct, and inferring that so far as matter may be endowed with the one property, it must be wanting in the other ? Have you ever known electricity to pass through a pane of sound glass? My knowledge and experience create an impres- sion that a coated pane is never discharged through the glass un- less it be cracked or perforated. That the property by which glass resists the passage of electricity, can be confounded with that which enables a metallic wire to permit of its transfer, agree- ably to Wheatstone's experiments, with a velocity greater than that of the solar rays, is to my mind inconceivable. You infer that the residual charge of a battery arises from the partial penetration of the glass by the opposite excitements. But if glass be penetrable by electricity, why does it not pass through it without a fracture or perforation ? According to your doctrine, induction consists " in a forced state of polarization in contiguous rows of the particles of the glass" (1300); and since this is propagated from one side to the other, it must of course exist equally at all depths. Yet the partial penetration suggested by you, supposes a collateral affection of the same kind, extending only to a limited depth. Is this con- sistent ? Is it not more reasonable to suppose that the air in the vicinity of the coating gradually relinquishes to it a portion of free electricity, conveyed into it by what you call "convection." The coating being equally in contact with the air and glass, it appears to me more easy to conceive that the air might be pene- trated by the excitement, than the glass. In paragraph 1300, I observe the following statement: uWhen a Leyden Jar is charged, the particles of the glass are forced into this polarized and constrained condition by the electricity of A letter to Prof. Faraday. 7 the charging apparatus. Discharge is the return of the parti- cles to their natural state, from their state of tension, whenever the two electric forces are allowed to be disposed of in some other direction." As you have not previously mentioned any particu- lar direction in which the forces are exercised during the preva- lence of this constrained condition, I am- at a loss as to what meaning I am to attach to the words "some other direction." The word some, would lead to the idea that there was an uncer- tainty respecting the direction in which the forces might be dis- posed of; whereas it appears to me that the only direction in which they can operate, must be the opposite of that by which they have been induced. The electrified particles can only " return to their natural state" by retracing the path by which they departed from it. I would suggest that for the words uto be disposed of in some other di- rection," it would be better to substitute the following, " to com- pensate each other by an adequate communication." Agreeably to the explanation of the phenomenon of coated electrics afforded in the paragraph above quoted (1300), by what process can it be conceived that the opposite polarization of the surfaces can be neutralized by conduction through a metallic wire ? If I understand your hypothesis correctly, the process by which the polarization of one of the vitreous surfaces in a pane produces an opposite polarization in the other, is precisely the same as that by which the electricity applied to one end of the wire extends itself to the other end. I cannot conceive how two processes severally producing re- sults so diametrically opposite as insulation and conduction, can be the same. By the former, a derangement of the electric equilibrium may be permanently sustained, while by the other, all derangement is counteracted with a rapidity almost infinite. But if the opposite charges are dependent upon a polarity indu- ced in contiguous atoms of the glass, which endures so long as no communication ensues between the surfaces; by what con- ceivable process can a perfect conductor cause a discharge to take place, with a velocity at least as great as that of the solar light ? Is it conceivable that all the lines of " contra-induction" or depolarization can concentrate themselves upon the wire from each surface so as to produce therein an intensity of polarization proportioned to the concentration; and that the opposite forces 8 A letter to Prof. Faraday. resulting from the polarization are thus reciprocally compensa- ted ? I must confess, such a concentration of such forces or states, is to me difficult to reconcile with the conception that it is at all to be ascribed to the action of rows of contiguous pon- derable particles. Does not your hypothesis require that the metallic particles, at opposite ends of the wire, shall in the first instance be subjected to the same polarization as the excited particles of the glass; and that the opposite polarizations, transmitted to some intervening point, should thus be mutually destroyed, the one by the other ? But if discharge involves a return to the same state in vitreous particles, the same must be true in those of the metallic wire: Wherefore then are these dissipated, when the discharge is suffi- ciently powerful ? Their dissipation must take place either while they are in the state of being polarized, or in that of re- turning to their natural state. But if it happen when in the first mentioned state, the conductor must be destroyed before the opposite polarization upon the surfaces can be neutralized by its intervention. But if not dissipated in the act of being polarized, is it reasonable to suppose that the metallic particles can be sundered by returning to their natural state of depolarization ? Supposing that ordinary electrical induction could be satisfac- torily ascribed to the reaction of ponderable particles, it cannot, it seems to me,-be pretended that magnetic and electro-magnetic induction is referable to this species of reaction. It will be admitted that the Faradian currents do not for their production require intervening ponderable atoms. From a note subjoined to page 37 of your pamphlet, it appears that " on the question of the existence of one or more imponder- able fluids as the cause of electrical phenomena, it has not been your intention to decide." I should be much gratified if any of the strictures in which I have been so bold as to indulge, should contribute to influence your ultimate decision. It appears to me that there has been an undue disposition to burden the matter, usually regarded as such, with more duties than it can perform. Although it is only with the properties of matter that we have a direct acquaintance, and the existence of matter rests upon a theoretic inference that since we perceive properties, there must be material particles to which those prop- erties belong ; yet there is no conviction which the mass of man- A letter to Prof. Faraday. 9 kind entertain with more firmness than that of the existence of matter in that ponderable form, in which it is instinctively recog- nized by people of common sense. Not perceiving that this con- viction can only be supported as a theoretic deduction from our perception of the properties; there is a reluctance to admit the existence of other matter, which has not in its favor the same instinctive conception, although theoretically similar reasoning would apply. But if one kind of matter be admitted to exist because we perceive properties, the existence of which cannot be otherwise explained, are we not warranted, if we notice more properties than can reasonably be assigned to one kind of mat- ter, to assume the existence of another kind of matter ? Independently of the considerations which have heretofore led some philosophers to suppose that we are surrounded by an ocean of electric matter, which by its redundancy or deficiency is capable of producing the phenomena of mechanical electricity, it has appeared to me inconceivable that the phenomena of gal- vanism and electro-magnetism, latterly brought into view, can be satisfactorily explained without supposing the agency of an inter- vening imponderable medium by whose subserviency the induc- tive influence of currents or magnets is propagated. If in that wonderful reciprocal reaction between masses and particles, to which I have alluded, the polarization of condensed or accumu- lated portions of intervening imponderable matter, can be brought in as a link to connect the otherwise imperfect chain of causes; it would appear to me a most important instrument in lifting the curtain which at present hides from our intellectual vision, this highly important mechanism of nature. Having devised so many ingenious experiments tending to show that the received ideas of electrical induction are inadequate to explain the phenomena without supposing a modifying influ- ence in intervening ponderable matter, should there prove to be cases in which the results cannot be satisfactorily explained by ascribing them to ponderable particles, I hope that you may be induced to review the whole ground, in order to determine whether the part to be assigned to contiguous ponderable parti- cles, be not secondary to that performed by the imponderable principles by which they are surrounded. But if galvanic phenomena be due to ponderable matter, evi- dently that matter must be in a state of combination. To 2 10 A letter to Prof. Faraday.- what other cause than an intense affinity between it and the metallic particles with which it is associated, can its confinement be ascribed consistently with your estimate of the enormous quantity which exists in metals ? If " a grain of water, or a grain of zinc, contain as much of the electric fluid as would supply eight hundred thousand charges of a battery containing a coated surface of fifteen hundred square inches," how intense must be the attraction by which this matter is confined ? In such cases may not the material cause of electricity be considered as latent agreeably to the suggestion of CErsted, the founder of electro- magnetism. It is in combination with matter, and only capable of producing the appropriate effects of voltaic currents when in act of transfer from combination with one atom to another; this transfer being at once an effect and a cause of chemical decompo- sition, as you have demonstrated. If polarization in any form, can be conceived to admit of the requisite gradations of intensity, which the phenomena seem to demand; would it not be more reasonable to suppose that it ope- rates by means of an imponderable fluid existing throughout all space, however devoid of other matter ? May not an electric cur- rent, so called, be a progressive polarization of rows of the electric particles, the polarity being produced at one end and destroyed at the other incessantly, as I understood you to suggest in the case of contiguous ponderable atoms. When the electric particles within different wires are polarized in the same tangential direction, the opposite poles being in prox- imity, there will be attraction. When the currents of polariza- tion move oppositely, similar poles coinciding, there will be repulsion. The phenomena require that the magnetized or polar- ized particles should be arranged as tangents to the circumference, not as radii to the axis. Moreover, the progressive movement must be propagated in spiral lines in order to account for rotary influence. Between a wire which is the mean of a galvanic discharge and another not making a part of a circuit, the electric matter which intervenes may, by undergoing a polarization, become the medium of producing a progressive polarization in the second wire moving in a direction opposite to that in the inducing wire ; or in other words an electrical current of the species called Faradian may be generated. A letter to Prof. Faraday. 11 By progressive polarization in a wire, may not stationary polar- ization, or magnetism be created ; and reciprocally by magnetic polarity may not progressive polarization be excited ? Might notthe difficulty, above suggested, of the incompetency of any imaginable polarization to produce all the varieties of elec- trical excitement which facts require for explanation, be sur- mounted by supposing intensity to result from an accumulation of free electric polarized particles, and quantity from a still greater accumulation of such particles, polarized in a latent state or in chemical combination ? There are it would seem many indications in favor of the idea that electric excitement may be due to a forced polarity, but in endeavoring to define the state thus designated, or to explain by means of it the diversities of electrical charges, currents and ef- fects, I have always felt the incompetency of any hypothesis which I could imagine. How are we to explain the insensibility of a gold leaf electroscope, to a galvanized wire, or the indiffer- ence of a magnetic needle to the most intensely electrified sur- faces ? Possibly the Franklinian hypothesis may be combined with that above suggested, so that an electrical current may be constituted of an imponderable fluid in a state of polarization, the two elec- tricities being the consequence of the position of the poles, or their presentation. Positive electricity may be the result of an accumulation of electric particles, presenting poles of one kind; negative, from a like accumulation of the same matter with a presentation of the opposite poles, inducing of course an oppo- site polarity. The condensation of the electric matter, within ponderable matter, may vary in obedience to a property analogous to that which determines the capacity for heat, and the differ- ent influence of dialectrics upon the process of electrical induc- tion may arise from this source of variation. With the highest esteem, I am yours truly, Robert Hare. h i