Elements of experimental and natural philosophy : being a familiar and easy introduction to the study of the physical sciences; embracing animal mechanics, pneumatics, hydrostatics, hydraulics, acoustics, optics, caloric, electricity, voltaism, and magnetism / by Jabez Hogg.

  • Hogg, Jabez, 1817-1899.
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: Elements of experimental and natural philosophy : being a familiar and easy introduction to the study of the physical sciences; embracing animal mechanics, pneumatics, hydrostatics, hydraulics, acoustics, optics, caloric, electricity, voltaism, and magnetism / by Jabez Hogg. Source: Wellcome Collection.

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    633 those of the magnet. A cylinder covered with photographic paper is so placed that the point of light may fall on it. The cylinder is carried roimd on its axis by clock-work, and, by the combined movements of the point of light and of the cylinder, the magnetic curve is self-traced upon the sensitive paper. The photographic process has also been applied to the barometer, and to the wet and dry bulb thermometers; but the mode of application is different from the preceding, the light not being reflected from a mirror. As the preparation of the sensitive paper used in these instruments differs somewhat from that adopted in ordinary photographic processes, it may not be inappropriate to describe it. The paper is first washed with a solution of four grains of isinglass, eight of iodide, and twelve of bromide of potas- sium, in one fluid ounce of distilled water, and dried quickly by the fire; a considerable quantity of paper may be thus pre- pared at once. Previously to being placed on the cylinder, the ■ paper is washed over with a solution of fifty grains of nitrate • of silver to one ounce of water, which communicates to it the • requisite degree of sensibility. After having been in action Ifor twenty-four hours, the paper is removed from the cylinder, 1 and the impression developed with a warm soliition of twenty { grains of galUc acid to one ounce of water, with a small addi- Ition of the ordinary commercial strong acetic acid: this is •subsequently fixed in the usual way with, hyposulphite of Isoda. The principle of the photographic part of the apparatus is jshown in the annexed cut (fig. 362), in which a represents a part of a bar magnet; b a concave mirror, resting in a stirrup ly attached to the suspension apparatus, the whole being pported by a single thread; e a blackened glass cylinder, rapped round with photographic paper; d a plano-convex .^ns ; c a lamp placed a little out of the line which joins the ntres of the cylinder and magnet. In operation a pencil of Vht passes from c* through a very narrow slit or aperture, 'verges and spreads over the mirror b, from which it is re- ected, and diverges to the lens d, and is condensed into ri ell-defined spot of light at the surface of the paper. The tion of this spot upon the photographic paper is to leave a CO, which is, however, imperceptible, until removed and veloped in the manner pointed out.