[104] _On the Polarization of the Chemical Rays of Light_: by John Sutherland, M.D., in which the author refers to the following experiment of M. J. E. Bérard--“I received the chemical rays directed into the plane of the meridian on an unsilvered glass, under an incidence of 35° 61'. The rays reflected by the first glass were received upon a second, under the same incidence. I found that when this was turned towards the south, the muriate of silver exposed to the invisible rays which it reflected was darkened in less than half an hour; whereas, when it was turned towards the west, the muriate of silver exposed in the place where the rays ought to have been reflected, was not darkened, although it was left exposed for two hours. It is consequently to be presumed that the chemical rays can undergo double refraction in traversing certain diaphanous bodies; and lastly, we may say that they enjoy the same physical properties as light in general.”--Philosophical Magazine, vol. xx. Dr. Leeson has stated that Daguerreotype pictures can be taken more readily under the influence of polarized light, than by ordinary radiation. [105] _On the Magnetization of Light, and the Illumination of Magnetic Lines of Force_: by Michael Faraday, D.C.L., F.R.S.--Philosophical Transactions, vol. cxxxvii.--The following remarks are to the point of doubt referred to in the text.--“The magnetic forces do not act on the ray of light directly and without the intervention of matter, but through the mediation of the substance in which they and the ray have a simultaneous existence; the substances and the forces giving to and receiving from each other the power of acting on the light. This is shown by the non-action of a vacuum, of air or gases, and it is also further shown by the special degree in which different matters possess the property. That magnetic force acts upon the ray of light always with the same character of manner, and in the same direction, independent of the different varieties of substance, or their states of solid or liquid, or their specific rotative force, shows that the magnetic force and the light have a direct relation; but that substances are necessary, and that these act in different degrees, shows that the magnetism and the light act on each other through the intervention of the matter. Recognising or perceiving _matter_ only by its powers, and knowing nothing of any imaginary nucleus abstract from the idea of these powers, the phenomena described must strengthen my inclination to trust in the views I have advanced in reference to its nature.”--Phil. Mag. vol. xxiv. [106] The invention of the camera obscura certainly belongs to Giambattista Porta, and is described in his _Magiæ Naturalis, sive de Miraculis Rerum Naturalium, Libri Viginti_; Antwerp, 1561. An English translation made in 1658 exists, but I have not seen it.