The Year-Book of Facts in Science and Art

The Year-Book of Facts in Science and Art

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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. 1851 edition. Excerpt: ...rays are brought to a focus by means of an achromatic object-glass, the author finds that the point of most intense heat is within the focus of the compound lens. In a direct experiment with a. 6-inch objectglass of Tu1ley's he found that black glazed paper was not burnt but only smoked when held two inches beyond the focus, --at 1 inch it took fire in 39 seconds, --at half an inch in 27, --at the focus in 24, --at a quarter of an inch within ihefocus in 11, --at half an inch within in 14, --and at 1 inch within in 19 seconds. Hence it follows, from the difierent positions of the principal foci of light and heat, that the eye-piece which makes the image rays parallel, leaves the hot rays divergent, and passes to some extent on the outside of the illuminating rays; when the eyehole becomes essentially important, not only for the general purpose of stopping out false light, but particularly for stopping out all injurious heat during the examination of the sun with large telescopes.--Atlzenwum, No. 1191. CAUSE or VARIATION IN THE ANGLES or CRYSTALS. M. J. NIoxLEs states that the cause is the intervention of foreign substances. In September, 1849, he pointed out this cause in the Variations of the angles of the prisms of sugar of gelatine: and he now adduces a new fact which readily allows of verifying the influence that a small quantity of foreign substances may exert on the crystalline form of bodies which are deposited in its presence. When a solution of chloride of cobalt containing an excess of sal-ammoniac is allowed to evaporate spontaneously, crystals of the last-mentioned salt are obtained which are more or less coloured, the angles of which are always near, but never 90: the difference often exceeds 7, and yet these crystals more

Product details

  • Paperback | 156 pages
  • 189 x 246 x 8mm | 290g
  • United States
  • English
  • black & white illustrations
  • 1236862643
  • 9781236862648