Rensselaer Union, Volume 9, Number 32, Rensselaer, Jasper County, 26 April 1877 — The Properties of Light and Color. [ARTICLE]

The Properties of Light and Color.

Thk idea that everything can be added to light by passing it through colored transparent substances, or by reflecting it from colored surfaces,; is utterly erroneous, and proceeds simply from ignorance of the nature of light. It has been proved by Isaac Newton, and since his time by innumerable experiments of various kinds, that pure white light, such as comes from the sun to us, contains all the colors, as well as heat and chemical activity, and that they may be separated, or the light analyzed, by simply passing it through a prism of a transparent substance. The possibility of such a separation • has . been , understood only since the adoption of the vibratory theory, which also explains the nature of the caloric, luminous, colored and chemical rays. According to this theory, the vibrations, when at comparatively low velocity, manifest themselves as heat only; when the vibrations are rapid pnough to produce 450,000,000,000 waves per second, they become visible as red light; Five hundred billions produce the sensation of orange, 550,000,000,000 that of yellow, and so on through green, blue aad violet, the latter resulting from 850,000,000,000 of vibratings per second. Vibrations still more rapid are invisible to the human eye, but their existence is demonstrated by their chemieal action, in the same way aS the invisible vibrations below 450,C00,000,000 per second manifest themselves as heat only.

Densely transparent media retard the light, and this retardation will affect the rapid vibrations more than those of slower velocity; and under certain circumstances such media will cause light to be deflected 'from its course in such a way that the most rapid vibrations Will be most deflected and the slowest least. This is the principle of refraction, by which light can be separated into its caloric,'chemical and luminous rays of different colors. The refraction of light, permitting the examination of the colors Into which it has been split up, is the fundamental principle of the spetrosedpe, by which the Nature of various luminous and illuminated substances can be determined. The apparent colors of objects are caused by their reflecting rays of vibrations of certain velocities, and neither reflecting hor absorbing others; and the hues or transparent colored objects are similarly produced. They pass only certain rays, and absorb the others; ana the reflected or transmitted color is then called the color ot the object In order to perceive such a hue, it is essential that the light by which it is illuminated contains that color; and this is directly demonstrable by illuminating objects with light of one color, when objects of all other colors will appear black or gray. Buch a light can, for instance, be produced by burning alcohol in which common salt has been mixed; this produces a pure yellow flame, ana objects of whatever color, when seen by daylight, if illuminated by* Such* a flame, will Only show this color. Human faces, for instance, have in this light a ghastly, death-like appearance.

An ordinary ns, lamp, or candle light is not a pure white, being deficient in blue rays, and has an excess of red, orange and yellow; a white object cannot, by such a light, be distinguished from a yellow one; light bltae hannot be distinguished from green, and dark blue looks almost black. In regard to the nature of colored Objects, yrhethqr painted or dyed, and of transparent media, such as colored glass or liquid solutions, the analysis of their colors by means of the spectroscope shows that what we call simple colors are. in most cases complex. Only those colors are pure and simple which we obtain by the prismatic refraction, namely, the spectroscopic colors. The blue cobalt glass,, for instance, which is now called mazarin glass, is proved by the spectroscope not to owe fts violet shade to the very refrangible and chemically active violet ray# at the extreme end of the prismatic (spectrum; but on the contrary, this part of the spectrum is totally absent front light passed through blue glass. The special shade Of tile mazarin glass is caused by the fact that its blue is, tempered by a considerable quantity of the less refrangible red rays at the other or caloric extremity of the spectrum, and even with a trace, of orange. Its blue is, therefore, of less chemical activity than the prismatic blue, and of course in all its functions, such as heat, chemical action,

ete.', to far bUnw tM driglnal unchanged ‘"wJ hare gone Into the detail, of these rather elementary matter* for the purpose of expoalng the ignorance those who ’sssasax have used blue glass long ago. In order to moderate the intensitr« the U«M forth® photographer, who poaseee comuioa settle zgsatagtefii an impediment and the ndceemuy“Ame of exposure is rather extended, tar fta UM than dtherwise. Tt ls itrita*? that foch errors can prevail for yean, «ffien a rimsolar spectrum, to de the saore With U sensitized surface under a series of colored strips of glass. The writer of this artic e < did this more than thirty year* ago by the Daguerrean process, and satisfied himscj# about tha following points: 1. The chemical effect of the prismatic spectrum extends, fqr iodide of silver, from beyond the violet 1h the blue. 2. W hen bromine is used in connection with the iodine, it extends to within the green. While the yellow and red rays appear* to have .no effect on silver compounds, but may possess it for other substances. 8. In photographing pigments there is the utmost, diversity in th® results, according to the nature, of the pigment—much greater than the differences in shade leqd ,ps .tp expect. A> a general thing, the pure reds, orange and yellow, such ha are produced by vermilion and chromato* lesd. are photogfoptacally inert, and give blacks. The blues are the most active, most ’of all being ttltoaMZrlne, pext the lakes. But even the. red carmine takes well, as it has a violet shade; butwmbng tlte bluee, those bofderIna on green take least, and hence foliage tends to give dark efitects. which are only slightly corrected by using bbomihe. 4. In using ;as negatives stripe of colored glass to print in sunlight, muefi depends on thehhadh and intensity of the color. In general, jthq.chemical effect followwthu prismatic series from red to blue; but,the. most effective bide glass is always found to be far inferiors the sunlight alone, pure and simple. And this fact is sufficient to settle the question about the special vlrttiei claithea’fof Mae glass: it cannot possibly have any not already possessed by sunlight. However, If people,, ate indiiced by its pretended curative properties to take sun baths, which they otherwise might neglect, they may be oftefi benefited by the salubrious influence of the radiation of the mighty orb/an influence which cannpt sufficiently be »P----preefate d; "but the blue glass would probably get the credit which exclusively be-' longs to glorious old Sol.— American'.