Positive ray

“ When energy has to be transferred from a charged atom to a corpuscle, the latter only receives a very small fraction of the energy of the atom, thus a very small fraction of the energy of the positive rays may be transformed into a kind available for light production. ”

“ In the positive rays in hydrogen the molecules frequently outnumber the atoms, but no radiation that can be attributed to the molecules has yet been detected.The spectrum of hydrogen is there, but as it does not show the Döppler effect it cannot be due to the molecules. ”

“ From the points of the triangle stream pencils of luminosity showing the characteristic red colour of the positive rays in helium, while the middle points of the sides are the origin of streams of greenish luminosity, the colour of the path of the cathode rays through helium. The difference In the character of the rays is also made evident by bringing a small magnet near the discharge tube; the green rays are visibly deflected by the magnet but no appreciable effect is produced on the red rays. ”

“ It is much better explained by supposing their eyes to be constructed to respond to wave-lengths either greater or less than those of mankind.
A ray of light, then, consists of a single line of undulations of a definite wave length, such that if it falls upon the eye it will produce sight; if it falls upon a thermo-pile it heats it by just the same quantity that another wave-length would heat it; if it falls upon matter in unstable chemical relations, it will do chemical work, depending upon the kinds of matter. A red ray is as effective for some substances as a violet ray is for others. ”

“ If the rays had any existence outside of the eye, they would still be seen; instead of which, the whole of them disappear when the luminous point, or, in the case of the street-lamp, when the flame, is covered by the screen. A second proof that the origin of the phenomenon is in the eye, and not in the object, is afforded by the fact that if, while attentively observing the rays, we incline the head, the rays turn with the eyes, so that when the head is resting on the shoulder the ray which appeared vertical becomes horizontal. ”

“ That both the compound rays of ordinary sunlight and ultra-violet rays (“artificial sunlight”) are highly effective in the treatment of a number of complaints is now well known. They are both in general use for the external treatment of rickets, tuberculosis, and a number of other diseases. Light-rays are also applied to hasten the healing of wounds. ”

“ A ray of light impinging upon a piece of black cloth is said to be absorbed. If only a part of the ray is absorbed, the rest being reflected, the parts of the ray reflected produce the sensation of color.
If a ray of light is passed through a wedge-shaped prism the component parts of the ray are unequally bent or refracted, and reach the eye in a series of colors. Red is the least refracted; violet suffers the greatest refraction. A ray of white light, therefore, is not of a “bundle” of wave-lengths of the same magnitude, but a bundle of an infinite number of rays of different wave-lengths. ”

“ It is proper to remark at this point that, when we analyze light in this way to examine it in its elements, we perform an operation entirely parallel to that of the chemist who separates the simple elements of a compound body. The elementary ray is a chemical species in light. It has all the characteristics of a species. It is incapable of decomposition, it has an individuality of its own, characterized by its wave-length, by the physiological effects it induces, whether acting alone or in association with other rays, and by the phenomena which it exhibits in its relations with bodies. ”

“ As to the eye itself, certain of the wave lengths are competent to produce the sensation we call light, but the same ray will heat the face of a thermopile or produce photographic effects if permitted to act upon the proper material, so there is no more propriety in calling it a light ray than in calling it a heat ray or an actinic ray. What the ray will do depends solely upon what kind of matter it falls upon, and all three of these names, light, heat, and actinism, are names of effects of radiant energy. ”

“ It is hardly necessary to occupy time with experiments in showing that a ray of light can be reflected and refracted by mirrors and prisms, and converged or diverged by transparent lenses. These are simple optical facts, and if you are not familiar with them it will be easy for you to make their acquaintance by studying any simple book upon optics; but I should like to draw your attention to the fact that, in addition to rays of light and electric radiation, we are acquainted with another kind of radiation, which is also susceptible of being refracted, and that is commonly called dark heat. ”

“ Those that exist beyond the red ray are capable of producing heat, while those that are beyond the violet excite chemical action. These invisible violet rays can be actually made perceptible to the eye, or, in other words, the undulations or waves proceeding from this end of the spectrum can be made to strike against certain substances and induce luminous vibrations, so as to connect the dark space beyond the violet with a brilliantly illuminated band. ”

“ But when certain other substances, such as sulphate of quinine, or a thin slip of uranium glass, are placed in the path of the rays, this rapid motion is arrested and modified, and these rays, which in themselves are not luminous, are reflected back to our eyes as luminous rays. The rapidity of the vibrations being moderated, our retinas become sensible to them as rays of blue light. ”

“ The rays on the further side of the red, not perceptible to our eyes—the so-called dark heat-rays—are likewise absorbed in their passage through the water, and an object at some depth under water would therefore only be reached by rays of high refrangibility, particularly blue rays. ”

“ And yet the waves of red light, measured by the amount of energy which they carry, are immensely more powerful than the waves of blue. The blue rays are usually called chemical rays—a misleading term; for, as Draper and others have taught us, the rays that produce the grandest chemical effects in nature, by decomposing the carbonic acid and water which form the nutriment of plants, are not the blue ones. ”

“ Hopefully no one finds it problematic, that I treat a light ray almost as a ponderable body. That light rays possess all absolute properties of matter, can be seen at the phenomenon of aberration, which is only possible when light rays are really material. — And furthermore, we cannot think of things that exist and act on our senses, without having the properties of matter. ”

“ Ultra-violet rays affect life. The amount of ultra-violet coming from the sun is variable. Does this mean that some of the obscure, day by day variations of health can be due to this? Some days everybody seems happy and cheerful. ”

“ These colored rays are now known to be the sources of all the tints by which nature adorns the surface of the earth, or art imitates, in its desire to create the beautiful. These colored bands have not the same illuminating power, nor do they possess the same heat-giving property. The yellow rays give the most LIGHT; the red rays have the function of HEAT in the highest degree. ”

“ Synthetic sunlight produced by him with an electric arc light of his own invention proved as good as natural sunlight, and could be better regulated to the patient’s endurance. He used two distinct kinds of light-rays, the short ultra-violet rays for nerve nutrition, and the long red and infra-red rays for muscle treatment. Red rays, as can be seen when the hand is held up against the sunlight, penetrate the flesh to a considerable extent, and can therefore stimulate the sleeping muscle. ”

“ This quality, which varies to infinity, occasions the different kinds of rays to unite in every possible manner, and every possible proportion; and hence the inexhaustible variety of shades and hues which nature has diffused over the landscape of the world. When a body absorbs nearly all the light which reaches it, that body appears black. It transmits to the eye so few reflected rays that it is scarcely perceptible in itself, and its presence and form make no impression upon us, unless as it interrupts the brightness of the surrounding space. ”

“ The general trend of the discussion in the literature has been that the rays of the sun lying in the region of the spectrum comprising the violet and ultraviolet are of the greatest importance in determining the influence of insolation upon human beings, and these rays have a special, though undeserved, designation as actinic rays. ”

“ Then, again, if we look at faint stars, they do not grow any brighter as we look. Each ray sends its message to the brain, and that is all; we cannot heap them up in our eye, and, indeed, after a time we see less, because our nerves grow tired. But on a photographic plate in a telescope, each ray in its turn does a little work upon the chemicals, and the longer the plate remains, the stronger the picture becomes. ”

“ It is known that out of every 10,000 rays issuing from the sun, and penetrating space at the calculated rate of 200,000 miles in each second of time, about one-fifth part is altogether lost and absorbed in passing through the atmosphere, and never reaches the outer envelope of the human eye. It is also known that of the rays that proceed from the sun, some produce light, some heat, and some a peculiar kind of chemical action to which the marvels of photography are due. ”

“ That comprehends more truth, but it is not yet the Truth. Only when the giant lens shall have recombined the split-up rays, and when the invisible, chemical and heat rays have given proof of their own specific effects, will a view more [253] in accordance with the facts be able to arise, and men will perceive that the sun emits white light which is split up by the prism into differing rays with different peculiarities, which rays can be recombined by the lens into one mass of white light. ”

“ Nor does the optic nerve embrace the entire range even of radiation. Some rays, when they reach it, are incompetent to evoke its power, while others never reach it at all, being absorbed by the humours of the eye. To all rays which, whether they reach the retina or not, fail to excite vision, we give the name of invisible or obscure rays. ”

“ When white light is decomposed by the prism, we obtain seven groups of visible rays, of unequal refractive power, violet, indigo, blue, green, yellow, orange, and red. The spectrum or ribbon of colors thus obtained widens and spreads out by invisible radiations. Beyond the red, there exist radiations of dark heat, or calorific rays, and, outside of the violet, radiations which are called chemical or ultraviolet rays. The first affect the thermometer, the last occasion energetic reactions in chemical compounds. What is their influence upon vegetation? ”

“ As regards the penetration of light, assimilative rays useful to plant life probably do not reach beyond 150 fathoms. Photographic rays have been detected as low as 220 fathoms, and if any light penetrate beyond this depth, it will consist only of blue, violet and ultra-violet rays: it has been suggested that the red colour prevalent in many deep-sea animals may be a screen from these hurtful rays. ”

“ Of course, it is not denied that there is in each substance something that determines which are the rays absorbed, and which are the rays reflected to the eye—something that can destroy certain waves, but is powerless over others that rebound from the substance, and reaching the eye, there produce their characteristic impressions. And it is but this power of sending back only certain rays among the multitude which a sunbeam furnishes, that can be attributed to objects when we say that they have such or such a colour. ”

“ For the ray has really travelled from C to E, and from E to O, and it is that journey which determines the distance of the object; and hence we see ourselves as far beyond the mirror as we stand from it. Though a ray is here taken only from one part of the face, it may be easily 85 conceived that rays from every other part of the face must produce a similar effect. ”

“ In general, rays of light falling obliquely on any medium are bent as if they were attracted by it, when it has a greater density, or contains more of the inflammable principle, than the medium through which it was transmitted to it. More of the rays are reflected when they fall upon a body with a small degree of obliquity to its surface, and more of them are transmitted, or enter the body, when their incidence is nearer to a perpendicular. ”

“ Ordinary light—according to the undulatory theory—is due to vibrations transverse to the direction of the ray, but varying so rapidly as to show no particular direction of their own, the fronts of the light-waves crisscrossing at all angles. ”

“ Do the Sun's Rays put out the Fire (Vol. vii., p. 285.) .—It is known that solar light contains three distinct kinds of rays, which, when decomposed by a prism, form as many spectra, varying in properties as well as in position, viz. luminous, heating or calorific, and chemical or actinic rays.
The greater part of the rays of heat are even less refrangible than the least refrangible rays of light, while the chemical rays are more refrangible than either. ”

“ As these light rays have been characterized as invisible, it may be difficult to understand how invisible rays can cast a visible shadow, and it should be here stated that when these unseen rays fall upon certain chemical substances the latter are made to glow with a peculiar fluorescence, and a screen made of such fluorescing materials will light up where the rays fall upon it, and remain dark at the points where the rays are intercepted by a substance opaque to such rays, thus outlining a shadow. ”

“ By the other view, or the corpuscular hypothesis, the beam of white light is supposed to consist of certain coloured rays, each of which has physical properties peculiar to itself, and thus is capable of producing different physiological effects. These rays falling upon a transparent or an opaque body suffer more or less absorption, and being thus dissevered, we have the effect of colour. A red body absorbs all the rays but the red ”