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. 1846 edition. Excerpt: ...bodies in right lines with inconceivable velocity. According to the undulatory theory of more recent writers, light has no material existence, but its effects are produced by vibrations, or undulations, of a subtil ethereal medium universally diffused through nature; according to this view, the phenomena of light are produced by pulsations of ether on the retina of the eye, as those of sound are by pulsations of air on the nerve of hearing. Whatever may be the nature or cause of light, it has certam properties or effects which we are enabled to investigate. Thus, wo can determine, experimentally, the laws by which it is governed in its passage through different transparent substances, and also those by which it is governed when it strikes a substance through which it cannot pass. We are also enabled to test its nature, to a certain degree, by decomposing or dividing it into its elementary parts. 396. Luminous bodies are such as emit, or excite the perception of, light from their own substance. Of this kind are the sun, the stars, terrestrial flames of all kinds, phosphorescent bodies, and those substances which shine by being heated, or by friction. Non-luminous bodies are those which have not the power of emitting, or exciting the sensation of, light from their own substance, but possess the property of reflecting the light which is cast upon them from luminous bodies. To this class belong the moon and planets, which shine by reflecting the light of the sun. Non-luminous bodies may illuminate each other, but their reflected light is inferior, in point of brilliancy, to that which proceedsfrom luminousbodies. 397. " Transparent bodies are such as permit the rays of light to pass freely through them. Air and some of the gases are...