Sir William Crookes
Published: 2013-09
Total Pages: 474
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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1861 edition. Excerpt: ...for this and the succeeding experiments, was the powerful one constructed by Mr. Saxton for the Gallery of Practical Science in Adelaide Street. To render it convenient for these experiments, that is, to ensure the appearance of the spark always at the same point, thefollowing temporary alteration was made: --The place of the revolving star was supplied by a small oval disc, which while it revolved acted on ono arm of a lever, beneath which a spring was placed like that to a flute key; this lever was fixed on a plato of sheet-iron, having at its extremity a small cup to hold the mercury, and the other end of the lever was bent at right angles, so that as the oval disc revolved the bent end of the lever was alternately dipped into the metal and removed, and tho spark always occurred precisely at the same point. Another advantage was obtained by this arrangement, --Chemical Niwvi March jo, 1861.) On Electric, Voltaic, and Electro-Magnetic Sparks. 199 the mercury was not thrown out of the cup as it is in tho ordinary disposition of the apparatus. III. I next proceeded to observe the prismatic analysis of the electro magnetic spark taken from different metals while in a fluid state. For this purpose I employed the following metals in the purest state I could obtain them: --Zinc, cadmium, bismuth, tin, and lead. I placed the metal intended to he the subject of experiment in the cup formed in the iron plate, and melted it by the application of a spirit-lamp placed beneath; the spark was then taken as above described. Not having at my disposal an instrument like that which Frauenhofer employed in his experiments, by which the degrees of refrsngibility might bo absolutely measured, I was obliged to content myself with an ordinary..