NATURAL PHILOSOPHY". 149 



We cannot doubt that the great loss of light proved by the experiments 

 above given, is to be, in part at least, accounted for by the conversion of a 

 portion of the light into heat, an effect perfectly in harmony with the the- 

 ory of transverse vibrations as applied to explain the phenomena of polari- 

 zation of heat. On this theory, heat and light are different effects produced 

 by one and the same cause, and they differ physically only in the rapidity 

 and amplitude of their vibrations. The screen through which the vibrations 

 of light are propagated serves to diminish, first the rapidity of the vibrations 

 requisite to produce the most infrangible rays, and in proportion as the trans- 

 parency of the screen is diminished by any cause, inherent or superficial, 

 this arrest becomes more and more complete. As the more rapid ethereal 

 vibrations have probably the least amplitude, we infer from analogy in sound- 

 waves, that as waves of least intensity have the greatest amplitude, so with 

 the luininiferous ether the extreme red has but little brilliancy. Hence the 

 loss of light from polished screens is small compared with that observed in 

 screens of opaline or roughened glass. It would be instructive to examine 

 the spectrum obtained from a pencil of rays under each of the cases given, 

 by means of a sulphide of carbon prism. 



The subjett of absorption of light by screens has long since been carefully 

 examined by Bouguer. By a photometric method essentially like Rum- 

 ford's, Bouguer measured the loss of light in the beam of a candle compared 

 with a flambeau, and also with the light of full-moon, in passing through 

 sixteen thicknesses of common window-glass having a united thickness of 

 21 '43 millimetres = -85 inch. The mean loss of light shown by these trials 

 was as 247 : 1, or over ninety-nine per cent of the whole quantity. 



Six plates of the purest mirror plate glass, having a united thickness of 

 15*128 millimetres, diminished the light in the ratio of 10 to 3, occasioning a 

 loss of about seventy per cent of diffuse daylight. A mass of very pure 

 glass, about three inches thick, diminished the light only about half the latter 

 amount, owing to its being a single mass, and not cut up into many planes. 



He also measured the absorbing power of sea- water for light, and found, as 

 the results of experiments made in France, and of observations also in the 

 torrid zone, that at the depth of three hundred and eleven French feet the 

 light of the sun would be equal only to that of the full moon, and at the 

 depth of six hundred aad seventy-nine feet would wholly disappear. He 

 estimates the transparency of the air as four thousand five hundred and 

 seventy-five times greater than that of sea-water; and from the properties of 

 a logarithmic curve (which he calls yraduhicique), whose functions he had 

 determined experimentally, he seeks to fix the outer limits of the atmosphere. 



OX A PROBABLE MEANS OF RENDERING VISIBLE THE CIRCULATION 



IN THE EYE. 



The following article is communicated to Silliman's Journal by Professor 

 Ogden W. Rood, of the Troy (N. Y.) University: 



Some time ago, while looking at a bright sky through three plates of 

 cobalt-glass, I saw with astonishment that the field of view was filled with, 

 and traversed in all directions by, small bodies resembling animalcules. 

 They were seen on the blue field as yellowish spots, and always appeared 

 elongated in the direction of their motion, which was, as a general thing, 

 tolerably uniform. The same result was obtained by experimenting upon 

 the eyes of a number of persons. Convex lenses of various foci, from three 



13* 



