Text-book of medical and pharmaceutical chemistry / by Elias H. Bartley.

  • Bartley, Elias Hudson, 1849-1937.
Date:
[1899, ©1898]
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of medical and pharmaceutical chemistry / by Elias H. Bartley. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

    43/748 (page 39)
    LIGHT. The second so-called physical force which plays an important part in many chemical phenomena is light. According to the best con- ception we have of light, it is the effect upon the optic nerve pro- duced by undulations of an exceedingly subtle and highly elastic form of matter, called the luminiferous ether. That this ether really exists, pervading the spaces between the molecules of all bodies, and being many million times more elastic than air, and so light that it offers no appreciable resistance to the earth moving noo miles a minute through it, is merely a hypothesis. It has been advanced to explain certain well-known facts. That light passes from the sun and stars to the earth, no one can doubt; and yet, without some assump- tion like the above, we can not conceive how it does so unless we hold to a former view, which taught that light is in itself a form of matter, without weight, given off by luminous bodies, and able to pass through glass, water, rocks, etc. These properties are contrary to all known laws of ordinary matter, as also are those of the ether assumed in the other theory. It is believed that undulations may originate in certain motions of molecules or atoms ; that these motions or undulations are communi- cated to the ether and conveyed upon it in the form of waves ; and that the movement described by a given particle of ether is, in the main, an oscillation at right angles or perpendicular to the direction of the ray or beam. Transmission of Light.—The motion of a ray of light travels along the line of particles very much in the same way that it passes along the line of ivory balls placed in contact on the billiard table when a ball strikes the end one directly in line with the rest. The motion or impulse passes along the line, but the ball at the opposite end is the only one seen to move. The transmission of force may be illustrated by placing ,_/ a ruler on the table, holding it firmly '--'' in place, with a marble in contact with one end, and with a hard body striking a short, quick blow at the other end. The stick, as a whole, does not move, but the jar will be felt to pass under the hand and the marble will move from its place. A frequent class-room illustration of the transmission of force is that represented in figure 10. A number of wood or ivory balls are suspended by cords so that they