Series XIX. CONTENTS. Par. ... § 26. On the magnetization of light and the illu- ¶ 1. Action of magnets on light............ 2146 Series XX. § 27. On new magnetic actions, and on the mag- 2243 3. Action of magnets on other substances acting magnetically on light ......... 2275 1. Crystalline polarity of bismuth 2457 2. Crystalline polarity of antimony...... 2508 3. Crystalline polarity of arsenic and general observations...... 6. On the position of a crystal of sulphate Series XXIV. § 30. On the possible relation of gravity to elec- ....... 2702 Series XXVIII. § 34. On lines of magnetic force; their definite character; and their distribution within a magnet and through space............ 3070 2. Revolving rectangles and rings... 3192 On the magnetic affection of light (repeated reflections) .... On the distinctions between the ferro-magnetic and diamagnetic On the diamagnetic conditions of flame and gases On the use of gutta percha in electrical insulation ... Observations on the magnetic force-law of distance (R. I.)... § 26. On the magnetization of light and the illumination of magnetic lines of force. i. Action of magnets on light. ¶ii. Action of electric currents on light. iii. General considerations. Received November 6,-Read November 20, 1845. Ti. Action of magnets on light. 2146. I HAVE long held an opinion, almost amounting to conviction, in common I believe with many other lovers of natural knowledge, that the various forms under which the forces of matter are made manifest have one common origin; or, in other words, are so directly related and mutually dependent, that they are convertible, as it were, one into another, and possess equi1 Philosophical Transactions, 1846, p. 1. 2 The title of this paper has, I understand, led many to a misapprehension of its contents, and I therefore take the liberty of appending this explanatory note. Neither accepting nor rejecting the hypothesis of an æther, or the corpuscular, or any other view that may be entertained of the nature of light; and, as far as I can see, nothing being really known of a ray of light more than of a line of magnetic force or electric force, or even of a line of gravitating force, except as it and they are manifest in and by substances; I believe that, in the experiments I describe in the paper, light has been magnetically affected, i. e. that that which is magnetic in the forces of matter has been affected, and in turn has affected that which is truly magnetic in the force of light by the term magnetic I include here either of the peculiar exertions of the power of a magnet, whether it be that which is manifest in the magnetic or the diamagnetic class of bodies. The phrase" illumination of the lines of : VOL. III. B valents of power in their action'. In modern times the proofs of their convertibility have been accumulated to a very considerable extent, and a commencement made of the determination of their equivalent forces. 2147. This strong persuasion extended to the powers of light, and led, on a former occasion, to many exertions, having for their object the discovery of the direct relation of light and electricity, and their mutual action in bodies subject jointly to their power; but the results were negative and were afterwards confirmed, in that respect, by Wartmann3. 2148. These ineffectual exertions, and many others which were never published, could not remove my strong persuasion derived from philosophical considerations; and, therefore, I recently resumed the inquiry by experiment in a most strict and searching manner, and have at last succeeded in magnetizing and electrifying a ray of light, and in illuminating a magnetic line of force. These results, without entering into the detail of many unproductive experiments, I will describe as briefly and clearly as I can. 2149. But before I proceed to them, I will define the meaning I connect with certain terms which I shall have occasion to use—thus, by line of magnetic force, or magnetic line of force, or magnetic curve, I mean that exercise of magnetic force which is exerted in the lines usually called magnetic curves, and which equally exist as passing from or to magnetic poles, or forming concentric circles round an electric current. By line of electric force, I mean the force exerted in the lines joining two bodies, acting on each other according to the principles of static electric induction (1161, &c.), which may also be either in curved or magnetic force" has been understood to imply that I had rendered them luminous. This was not within my thought. I intended to express that the line of magnetic force was illuminated as the earth is illuminated by the sun, or the spider's web illuminated by the astronomer's lamp. Employing a ray of light, we can tell, by the eye, the direction of the magnetic lines through a body; and by the alteration of the ray and its optical effect on the eye, can see the course of the lines just as we can see the course of a thread of glass, or any other transparent substance, rendered visible by the light and this is what I meant by illumination, as the paper fully explains.- December 15, 1845. M. F. 1 Experimental Researches, 57, 366, 376, 877, 961, 2071. : 2 Philosophical Transactions, 1834. Experimental Researches, 951-955. 3 Archives de l'Electricité, ii. pp. 596-600. straight lines. By a diamagnetic, I mean a body through which lines of magnetic force are passing, and which does not by their action assume the usual magnetic state of iron or loadstone. 2150. A ray of light issuing from an Argand lamp, was polarized in a horizontal plane by reflexion from a surface of glass, and the polarized ray passed through a Nichol's eye-piece revolving on a horizontal axis, so as to be easily examined by the latter. Between the polarizing mirror and the eye-piece two powerful electro-magnetic poles were arranged, being either the poles of a horse-shoe magnet, or the contrary poles of two cylinder magnets; they were separated from each other about 2 inches in the direction of the line of the ray, and so placed, that, if ou the same side of the polarized ray, it might pass near them; or if on contrary sides, it might go between them, its direction being always parallel, or nearly so, to the magnetic lines of force (2149.). After that, any transparent substance placed between the two poles, would have passing through it, both the polarized ray and the magnetic lines of force at the same time and in the same direction. 2151. Sixteen years ago I published certain experiments made upon optical glass1, and described the formation and general characters of one variety of heavy glass, which, from its materials, was called silicated borate of lead. It was this glass which first gave me the discovery of the relation between light and magnetism, and it has power to illustrate it in a degree beyond that of any other body; for the sake of perspicuity I will first describe the phænomena as presented by this substance. 2152. A piece of this glass, about 2 inches square and 0.5 of an inch thick, having flat and polished edges, was placed as a diamagnetic (2149.) between the poles (not as yet magnetized by the electric current), so that the polarized ray should pass through its length; the glass acted as air, water, or any other indifferent substance would do; and if the eye-piece were pre 1 Philosophical Transactions, 1830, p. 1. I cannot resist the occasion which is thus offered to me of mentioning the name of Mr. Anderson, who came to me as an assistant in the glass experiments, and has remained ever since in the Laboratory of the Royal Institution. He has assisted me in all the researches into which I have entered since that time, and to his cáre, steadiness, exactitude, and faithfulness in the performance of all that has been committed to his charge, I am much indebted.--M. F. |