Emission

“ Experience, finally, rectifying the vague predictions to which the most enlightened minds abandon themselves with so little reserve, shows that the calorific rays which emanate from the plane surface of a heated body have not the same force, the same intensity in all directions; that the maximum corresponds to the perpendicular emission, and the minimum to the emissions parallel to the surface.
Between these two extreme positions, how does the diminution of the emissive power operate? Leslie first sought the solution of this important question. ”

“ According to the theory of emission, the transmission of energy is effected by the actual transference of light-corpuscules from the luminous to the illuminated body, carrying with them their kinetic energy, together with any other kind of energy of which they may be the receptacles. ”

“ If an emission theory is accepted, it would seem most natural to assume that the excited portion of a reflecting mirror acts as a new source of light and that reflected light has the same velocity c with respect to the mirror as has original light with respect to its source. ”

“ With the emission of radiation it can go from stationary states with greater energy to others with less energy, ending its journey by remaining in the orbit which corresponds to the least possible energy. ”

“ If the deductions be in accordance with the facts, we accept the theory: if in opposition, the theory is given up. A single experiment is frequently devised, by which the theory must stand or fall. Of this character was the determination of the velocity of light in liquids, as a crucial test of the Emission Theory. ”

“ In the main, these facts may be summed up as the emission of certain radiations from known elemental matter: the material alpha particles with positive charge, the beta particles or negative electrons, and the gamma rays analogous to X rays. The emission of these rays results in the production of great heat. Then there is the law of transformations by which whole series of new elements are generated from the original element and maintain a constant equilibrium of growth and decay in the series. Lastly, we have the production of helium from the alpha particles. ”

“ It is only the presence of material bodies that by their continued emission and absorption can transform the surrounding radiation towards the unique constitution which corresponds to their temperature. We can define the temperature of an isolated field of radiation, of this definite ultimate constitution, to be the same as that of the material bodies with which it would thus be in equilibrium. ”

“ Again, the fact that hydrogen emits its characteristic radiations only when it is ionized or excited favors the theory that the process of emission is a process of settling down to a normal condition through a series of possible intermediate states, and is therefore in line with the view that a change in orbit is necessary to the act of radiation. ”

“ A. An atomic system possesses a number of states in which no emission of energy radiation takes place, even if the particles are in motion relative to each other, and such an emission is to be expected on ordinary electrodynamics. ”

“ There is no doubt that the process which takes place in the emission of radiation from the radioactive elements is a transformation of the element, an explosion of the atoms accompanied by the emission either of double-charged helium atoms or of electrons, and the forming of the atoms of a new element. The energy of the rays is an internal atomic energy, freed by these transformations. ”

“ According to an emission theory suggested by Stewart [3] light reflected from a mirror acquires a component of velocity equal to the velocity of the mirror image of the original source. Evidence disproving the possibility of such a principle will also be presented in this article.
A very complete emission theory of electromagnetism has been presented by Ritz. ”

“ What is important from the astrophysical point of view is the association of known lines in the spectrum with different levels of energy in the atom, these levels representing definite electron orbits. Absorption and emission of energy take place in an atom by the transfer of an electron from an orbit associated with low energy to an orbit associated with high energy, and vice versa. ”

“ In the same way that, for the purpose of knowing the constitution of matter, it first occurred to us to investigate gases, which appear to be molecular edifices built on a more simple and uniform plan than solids, we ought naturally to think that an examination of the conditions in which emission and absorption are produced by gaseous bodies might be eminently profitable, and might perhaps reveal the mechanism by which the relations between the molecule of the ether and the molecule of matter might be established. ”

“ It is necessary to admit an intermediary substance between the universe and ourselves? The od, a new imponderable, a sort of electricity, is perhaps nothing else. Its emissions explain the light that those who have been magnetised believe they see: the wandering flames in cemeteries, the forms of phantoms. ”

“ This limitation naturally caused inventors to search for methods by which the emission of light could be obtained from coal-gas otherwise than by the incandescence of the carbon particles contained within the flame itself. ”

“ The energy which is given to the electron by such an impulse is expended in the emission of the light waves and is thus transformed into radiation energy in the emitted light, while the electrons fall to rest again unless they receive in the meantime a new impulse. We can get an understanding of what these impulses in various cases may be by thinking of them, in the case of a glowing solid, for example, as due to the collisions of the molecules ”

“ Inasmuch as matter is the source of all heat and light radiations, the mechanism responsible for the emission and absorption of these radiations must be intimately related to the nature and constitution of matter itself and therefore theories of emission and absorption systems depend to a large extent upon our theories of the nature of atoms and molecules. ”

“ These electrons, which thus have a variable velocity, generate around themselves a transverse electromagnetic wave which is propagated with the velocity of light; for the charged particle becomes, as soon as it experiences a change of speed, the centre of a radiation. Thus is explained the phenomenon of the emission of radiations. In the same way, the movement of electrons may be excited or modified by the electrical forces which exist in any pencil of light they receive, and this pencil may yield up to them a part of the energy it is carrying. ”

“ In our day, when it is probable that force, motion, gravity, heat, light, electricity, magnetism, are simply modifications of one and the same agent, and the effect of the vibrations of that impalpable and invisible fluid known as ether, the assertion that the sun is the only fuel, the only force, must not call forth anywhere the smile of incredulity. All fuels, all forces, are to be regarded as only parts of the sun's heat. What is coal? ”

“ It shows us atoms of hydrogen or of sodium pulsating rhythmically with like oscillations in star-cloud or sun-cloud, and in London or Berlin. It exhibits to our eyes or to our scientific imagination a picture of the universe as a single whole, a picture of its evolution as a continuous process—one type of matter diffused throughout space; one gravitative attraction binding it together firmly in all parts; one multiform energy quivering through its molecules or traversing its ether, in many disguises of light, and heat, and sound, and electricity. ”

“ Limiting, then, our study to the molecular condition of a gas, picture to yourselves what must be the condition of our atmosphere, with its molecules flying about in all directions. Conceive what a molecular storm must be, raging about us, and how it must beat against our bodies and against every exposed surface. The molecules of our atmosphere move, on an average, nearly four (3.8) times slower than those of hydrogen under the same conditions; but then they weigh, on an average, fourteen and a half times more than hydrogen-molecules, and therefore strike with as great energy. ”

“ Now when the light we examine comes from a glowing solid, like white-hot iron, or a glowing liquid, or a gas under such enormous pressure that it behaves like a liquid, then the images of the slit always overlap each other, so that we see a continuous unbroken band of colour. However much you spread out the light you can never break up or separate the spectrum in any part. [2] But when you send the light, of a glowing gas such as hydrogen through the spectroscope, or of a substance melted into gas or vapour, such as sodium or iron vaporised by great heat, then it is a different story. ”

“ The recent experiments which indicate a change in the mass of an electron with the speed, together with the phenomenon of radioactivity, have in some minds created a doubt as to the exact validity of some of the most general laws of nature. In the following pages I shall attempt to show that we may construct a simple system of mechanics which is consistent with all known experimental facts, and which rests upon the assumption of the truth of the three great conservation laws, namely, the law of conservation of energy, the law of conservation of mass, and the law of conservation of momentum. ”

“ When a body loses energy by radiation, that energy is restored during an encounter; the way in which this energy is restored will profoundly affect the vibrations of the molecule, and hence the observed spectrum. I have endeavored by means of theoretical considerations, or speculations, as you may perhaps feel inclined to call them, to lead you on to an experimental law which I believe to be of very great importance. The spectrum of a molecule is in fact variable at any given temperature, and changes if the molecule is surrounded by others of different nature. ”

“ We thus see how the response is dependent on the molecular condition, and how a change of this condition may even give rise to a reversal of response, say, from a diminution to an increase of resistance. The nature of the chemical substance, the molecular condition, the intensity and duration of radiation, the pressure, the temperature, and even the electromotive force used for detection, are the factors which are instrumental in the modification of the final response. I have already shown [3] how the increasing effect of continuous radiation may produce molecular reversal. ”

“ Again, we find that the radiations which produce chemical change are more refrangible than either of the others, and the maximum of this power is found at the point where light rapidly diminishes, and where scarcely any heat can be detected: it extends in full activity, above its maximum, to a considerable distance, where no trace of light under ordinary conditions exists, and below that point, until light, appearing to act as an interfering agent, quenches its peculiar properties. ”

“ Every form, whether inorganic or organic, which we can discover within the limits of human search, is composed of atoms, which are capable of assuming, under the influence of certain physical forces, conditions essential to the physical state of that body of which they constitute a part. [1] The known forces, active in pro [Pg 5] ducing these conditions, are modes of motion; gravitation and aggregation, heat, light; and associated with these, actinism or chemical radiation; electricity, under all its conditions, whether static or dynamic ”

“ We can give a familiar illustration of gas in a state of extreme tenuity. Look at the beautiful incandescent light with which in these days our buildings are illuminated. How brilliantly those little globes shine! The globe has to be most carefully sealed against the outside air. If there were the smallest opportunity for access, the air from outside would rush in and the lamp would be destroyed. In the preparation of such a lamp elaborate precautions have to be taken to secure that the exhaustion of the air from the little globe shall be as nearly perfect as possible. ”

“ Of course, gases do radiate heat and light under some circumstances, but the radiation seems to be produced either by chemical action, as in the flames coloured by metallic vapours, or by electric discharge, as in vacuum tubes, the arc or the electric spark. ”

“ Perhaps we shall not greatly err if we regard a molecule as representing on a small scale something analogous to the solar system, while the various atoms which constitute the molecule may be likened to the various bodies of the solar system. The short historical sketch which we are about to give will embrace, therefore, along with energy, the progress of thought and speculation with respect to atoms and also with respect to a medium, inasmuch as these subjects are intimately connected with the doctrines of energy. ”

“ Soon after the introduction of gas as an illuminating agent it was realised that the luminosity of the flame is dependent on the presence of solid particles, which by the heat of combustion of the gas are raised to a temperature at which they emit radiations of wave-lengths corresponding to the ‘luminous rays’ of the spectrum. ”

“ Every elementary substance when in the gaseous state, and under low pressure, if brought to incandescence by heat, shines with light which, when dispersed, gives a discontinuous spectrum, made up of separate bright lines ”

“ By the impact of stars, by high speeds and collisions. In a collision any rate of heat generation may be attained. In a chemical process we are limited. When oxygen and hydrogen combine, they fall, metaphorically speaking, from a definite height. We cannot go very far with a blast, nor by confining heat in a furnace, but in an exhausted bulb we can concentrate any amount of energy upon a minute button. Leaving practicability out of consideration, this, then, would be the means which, in my opinion, would enable us to reach the highest temperature. ”