Identifier: s03philosophicalmag36londuoft (find matches)
Title: The Philosophical magazine; a journal of theoretical, experimental and applied physics
Year: 1798 (1790s)
Authors:
Subjects: Physics
Publisher: London Taylor & Francis (etc.)
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: Ontario Council of University Libraries and Member Libraries

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ords which pass over two other larger pulleys; these are ofwood ; they are both 15 centimetres in diameter, and are fixedupon a common axis, which is furnished with a small handle.Lastly, the cords are arranged so that the two brass pul-leys, and consequently the two discs, turn in the same direc-tion. This system is similar to that of the anorthoscope^as it has been presented to the public, except the equalityin diameter of the brass pulleys, the community of directionof their motions, the less number of the openings of theblack disc, and the greater width of these openings. Likethe anorthoscope also, the present instrument must be em-ployed in the evening, and strongly illumined by a good lamp * From the Bulletin de IAcad, de Bruxellcs, vol. xvi. p. 424. ^ In order that,-in the disc thus varnished, the tints of the colouredparts may remain very bright when observed by transmission, it is well forthe colours to be applied on both sides of the paper. Phil. Mag. S. 3. Vol. xxxvi. PL U.
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071 the Permanetice of Impressions on the JRetiyia. ^So conveniently placed behind the coloured disc; lastly, the ob-server must also place himself on the other side of the appa-ratus, that is to say, opposite to the black disc, keeping hiseyes on a level with the centres of the discs, whilst anotherperson turns the handle with sufficient rapidity. The di-stance of the observer from the apparatus must be a metre atleast. With this arrangement, let us imagine, for an instant, thatthe diameters of the two brass pulleys are mathematicallyequal, that the same is the case with the two wooden pulleys,and that the thicknesses of the two cords are also exactlyalike. Then the velocities of the two discs will be perfectlyequal; and as they are in the same direction, it is clear thatif, at the commencement of the movement, the two openingscorrespond, for example, to the red sectors, they will continueto correspond with them indefinitely; so that, if the velocity issufficient, the observer will s

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