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26 April 24th The apparatus being so arranged as to produce a dark field, the glasses with the contained liquid being introduced, a line of light was observed along the edge of the water. The effect appeared to be that of depolarization, but I should desire to make a number of experiments before asserting probably that the phenomenon was the one which I anticipated. Colours were also observed which were probably due [[strikethrough]] I was about to say [[/strikethrough]] to the curve of the water [[strikethrough// but this could not be the case since [[/strikethrough]] They say as it [[strikethrough]] extend one side [[/strikethrough]] passed from the [[strikethrough [[second?]] [[/strikethrough]] second side of the first curves of the [[circled]] meniscus [[/circled]] would be refracted from the perpendicular and as it entered the first surface of the 2nd limb of the same would be bent in the same direction. So that both limbs of the [[circled]] meniscus [[/circled]] would act as a prism to refract the light and produce colours but I do not see that a bright lining of light could be produced in this way so as to exhibit the appearance of depolarization. The only defect in the experiment which strikes me at present is that the field was not perfectly dark the polarization was effected by one of Nichol's prisms or rather Nichol's polarizing eye pieces. I intend to repeat the experiment with a darker ground produced by the polarization of a tourmaline. [[end page]] [[start page]] April 27th 1843 27 Commenced to day to experiment with the apparatice of Mallone, made for me by Rumkhorff of Paris. The cost of this set of articles, including a file of a single row of elements for determining the heat of the different parts of the solar spectrum, was 90 [[francs?]]. The galvanometer is furnished with an article for increasing to [[?]] consisting of two magnets to be placed on the top of the glass cover, and which, by being separated at their lower extremities, act with increasing power on the compound needle below and thus render it approximately nearer a perfect [[?]] state. The result of the experiments made with this apparatus are very satisfactory. It exhibits polarization of heat by means of two bundles of mica, also depolarization by placing between the bundles a plate of mica. Also the different transmissive power of different substances. particularly those of alum and common salt. I was much surprised at the effect produced by one of the articles. It consists of a pile of mica plates moveable around an axis and adjustable to any angle by means of a graduated arc. When the pile of mica was placed perpendicularly to the beam of heat, the needle stood at about 4°, but when it was placed so as to make an angle with the beam of about 33°, then the needle stood at 13 or 14°. This phenomenon is mentioned by Mallone in his article on polarization transcribed into the scientific memoirs. The explanation appears to be that the heat which passes the first lamina of mica is partially polarized, and is then in a proper condition to pass the next plate, which is placed at the polarizing angle. The same effect is produced by the transmission of light, if the article of apparatus by [[?]] before a beam of light at right angles to the same, and afterward turned into an angle of 33°, with it a great increase will be perceived in the quantity of transmitted light.
