The London dispensatory, containing: I, the elements of pharmacy; II, the botanical description ... and medicinal properties, of the substnaces of the materia medica; III, the pharmaceutical preparations and compositions of the London, Edinburgh, and Dublin Colleges of Physicians ... a practical synopsis of materia medica, pharmacy, and therapeutics : illustrated with many useful tables and copper-plates of pharmaceutical apparatus / by Anthony Todd Thomson.

  • Thomson, Anthony Todd, 1778-1849.
Date:
1818
Catalogue details

Licence: Public Domain Mark

Credit: The London dispensatory, containing: I, the elements of pharmacy; II, the botanical description ... and medicinal properties, of the substnaces of the materia medica; III, the pharmaceutical preparations and compositions of the London, Edinburgh, and Dublin Colleges of Physicians ... a practical synopsis of materia medica, pharmacy, and therapeutics : illustrated with many useful tables and copper-plates of pharmaceutical apparatus / by Anthony Todd Thomson. Source: Wellcome Collection.

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    A ray of light falling upon a polished surface is reflected from it at an angle equal to the angle of its incidence. When a ray of light moving in a straight line passes within a certain distance of a body parallel to its direction, it bends towards the body, or is inflected; but when the body parallel to its course is at a greater distance, the ray is bent from it, or deflected. When it passes obliquely from one medium to an¬ other of a different density, it is bent a little from the line of its former direction, and assumes a new one, or is refracted. In passing into a denser medium it is refracted towards the per¬ pendicular ; but from the perpendicular when passing into a rarer medium. The refraction is proportional to the density of the medium, but in that of a combustible the refraction is greater than the ratio of its density. Every ray of light is resolvable into seven other distinct rays, each possessing a different degree of refrangibility; and con¬ sequently divisible from each other by the prism. The ulti¬ mate or component rays are distinguishable by the impression of colours they excite on the eye; and are arranged in the fol¬ lowing order, red, orange, yellow, green, blue, indigo, violet. The red is the least refrangible, reflexible, and inflexible; the violet the most; and that of the others follow s the order in which they are placed. The colour of bodies depends on their trans¬ mitting or reflecting those rays only which excite the impres¬ sions of their colour. The reflection of the whole prismatic rays constitutes white; the absorption or suffocation of all or the greater part of these occasions black, which is the total absence of light. The illuminating power of the rays of light differs. Those towards the middle of the prismatic spectrum, as above ar¬ ranged, possess the greatest illuminating power; but this diminishes as the rays approach towards the extremities. Light enters into combination with bodies; and in some cases is again extricated without any change being produced, as in pyropliori, or substances which absorb light, and emit it again when carried into a dark place. In some cases, how¬ ever, the absorption of light by bodies occasions very sensible changes in them : the colour of plants, for example, their taste and odour, and the quantity of combustible matter they con¬ tain, depend on light: for a plant reared in the dark is nearly colourless, insipid, inodorous, and contains a very small pro¬ portion of combustible matter. The natural sources ofiight are the sun and fixed stars; but it is also artificially produced by combustion, chemical combi¬ nation, heat, and percussion. The sun’s rays, the greatest source of light, have been found to be composed of three difi- b 3