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LONDON Physical Society, May 8.-Prof. Gladstone, F.R.S., president, in the chair.—Mr. Crookes, F.R.S., exhibited and described some very important experiments on attraction and repulsion resulting from radiation, which he has recently submitted to the Royal Society, and of which an account has already been given in this journal (vol. xi. p. 494). It is unnecessary therefore to describe them at length, but it may be pointed out that the most beautiful of the instruments is one which Mr. Crookes calls a radiometer. It consists of four arms suspended on a steel point resting in a cup so that they are capable of revolving horizontally. To the extremity of each arm is fastened a thin disc of pith, lampblacked on one side, the black and white faces alternating. The whole is enclosed in a glass globe, which is then exhausted as perfectly as possible and hermetically sealed. Several of these instruments varying in delicacy were exhibited, and experiments made showing the influence of light and heat of different degrees of refrangibility, and in proof of the law of inverse squares, & c.-The President, in expressing the cordial thanks of the Society, referred to Mr. Crookes' statement that the repulsion was proportional to the length of the vibrations, and asked whether at the red end of the spectrum there was an abrupt termination of the action, and a gradual diminution towards the ultra violet.—Mr. Walenn inquired as to the action of the magnet and of different axes of crystals in causing repulsion.-Prof. Woodward made some observations with reference to the manipulation.-Prof. Guthrie paid a graceful compliment to Mr. Crookes' work, and observed that researches might be divided into two classes; those in which the value of the work outweighed the merit of the author, and those in which a result of comparatively trifling significance is the outcome of years of patient labour. He expressed a strong conviction that Mr. Crookes' research had, in an almost unparalleled degree, both elements of greatness.—Mr. Crookes stated, in reply to Dr. Gladstone's question, that the glass envelope of the radiometer must be taken into account in considering the action of the rays of different refrangibility, and further, that the increased effect due to red light may have been in part due to the concentration of rays of low refrangibility which attends the use of glass prisms. A diffraction spectrum might give a different result. Ke added that when a ray falls on a surface capable of motion, which reflects it, very little work is done, but if the surface quenches the ray, motion is produced. He then thanked Prof. Guthrie for his kindly remarks.—Prof. Cornu, of the Ecole Poly-technique, described his recent experiments on the determination of the velocity of light. He gave an account of the method of Fou-cault, and exhibited the complete apparatus, including the arrangement of mirrors for multiplying the distance traversed between the two reflections from the revolving mirror (NATURE, vol. xi. p. 274). -Prof. Adams, vice-president, mentioned that M. Cornu had contributed in no small measure to the success which had attended the formation in France of a society closely corresponding to our British Association, and assured him that the Physical Society felt grateful for his presence, as he could well understand the difficulties with which the early days of such a society are beset. —M. Cornu stated, in answer to a question of Prof. G. C. Foster, that he objected to the revolving mirror method, because the distance to be traversed by the light was very small, and because the path of the ray lay through a vortex of air produced by the rapid revolution of the mirror.
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Societies and Academies . Nature 12, 58–60 (1875). https://doi.org/10.1038/012058b0
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DOI: https://doi.org/10.1038/012058b0