Darwin and Modern Science [389]
terminals through a glass vessel containing air at very low pressure, it is found that rectilinear rays, known as cathode rays, proceed from the surface of the cathode or negative terminal. Where these rays strike solid objects, they give rise to the Rontgen rays now so well known; but it is with the cathode rays themselves that we are concerned. When they strike an insulated conductor, they impart to it a negative charge, and Thomson found that they were deflected from their path both by magnetic and electric forces in the direction in which negatively electrified particles would be deflected. Cathode rays then were accepted as flights of negatively charged particles, moving with high velocities. The electric and magnetic deflections give two independent measurements which may be made on a cathode ray, and both the deflections involve theoretically three unknown quantities, the mass of the particles, their electric charge and their velocity. There is strong cumulative evidence that all such particles possess the same charge, which is identical with that associated with a univalent atom in electrolytic liquids. The number of unknown quantities was thus reduced to two--the mass and the velocity. The measurement of the magnetic and electric deflections gave two independent relations between the unknowns, which could therefore be determined. The velocities of the cathode ray particles were found to vary round a value about one-tenth that of light, but the mass was found always to be the same within the limits of error, whatever the nature of the terminals, of the residual gas in the vessel, and of the conditions of the experiment. The mass of a cathode ray particle, or corpuscle, as Thomson, adopting Newton's name, called it, is about the eight-hundredth part of the mass of a hydrogen atom.
These corpuscles, found in so many different kinds of substance, are inevitably regarded as a common constituent of matter. They are associated each with a unit of negative electricity. Now electricity in motion possesses electromagnetic energy, and produces effects like those of mechanical inertia. In other words, an electric charge possesses mass, and there is evidence to show that the effective mass of a corpuscle increases as its velocity approaches that of light in the way it would do if all its mass were electromagnetic. We are led therefore to regard the corpuscle from one aspect as a disembodied charge of electricity, and to identify it with the electron of Lorentz and Larmor.
Thus, on this theory, matter and electricity are identified; and a great simplification of our conception of the physical structure of Nature is reached. Moreover, from our present point of view, a common basis for matter suggests or implies a common origin, and a process of development possibly intelligible to our minds. The idea of the evolution of matter becomes much more probable.
The question of the nature and physical meaning of a corpuscle or electron remains for consideration. On the hypothesis of a universal luminiferous aether, Larmor has suggested a centre of aethereal strain "a place where the continuity of the medium has been broken and cemented together again (to use a crude but effective image) without accurately fitting the parts, so that there is a residual strain all round the place." (Larmor, loc. cit.) Thus he explains in quasi-mechanical terms the properties of an electron. But whether we remain content for the time with our identification of matter and electricity, or attempt to express both of them in terms of hypothetical aether, we have made a great step in advance on the view that matter is made up of chemical atoms fundamentally distinct and eternally isolated.
Such was the position when the phenomena of radio-activity threw a new light on the problem, and, for the first time in the history of science, gave definite experimental evidence of the transmutation of matter from one chemical element to another.
In 1896 H. Becquerel discovered that compounds of the metal uranium continually emitted rays
These corpuscles, found in so many different kinds of substance, are inevitably regarded as a common constituent of matter. They are associated each with a unit of negative electricity. Now electricity in motion possesses electromagnetic energy, and produces effects like those of mechanical inertia. In other words, an electric charge possesses mass, and there is evidence to show that the effective mass of a corpuscle increases as its velocity approaches that of light in the way it would do if all its mass were electromagnetic. We are led therefore to regard the corpuscle from one aspect as a disembodied charge of electricity, and to identify it with the electron of Lorentz and Larmor.
Thus, on this theory, matter and electricity are identified; and a great simplification of our conception of the physical structure of Nature is reached. Moreover, from our present point of view, a common basis for matter suggests or implies a common origin, and a process of development possibly intelligible to our minds. The idea of the evolution of matter becomes much more probable.
The question of the nature and physical meaning of a corpuscle or electron remains for consideration. On the hypothesis of a universal luminiferous aether, Larmor has suggested a centre of aethereal strain "a place where the continuity of the medium has been broken and cemented together again (to use a crude but effective image) without accurately fitting the parts, so that there is a residual strain all round the place." (Larmor, loc. cit.) Thus he explains in quasi-mechanical terms the properties of an electron. But whether we remain content for the time with our identification of matter and electricity, or attempt to express both of them in terms of hypothetical aether, we have made a great step in advance on the view that matter is made up of chemical atoms fundamentally distinct and eternally isolated.
Such was the position when the phenomena of radio-activity threw a new light on the problem, and, for the first time in the history of science, gave definite experimental evidence of the transmutation of matter from one chemical element to another.
In 1896 H. Becquerel discovered that compounds of the metal uranium continually emitted rays