The point intended to be set forth for the consideration of the hearers was whether it was not possible that the vibrations—which in a certain theory are assumed to account for radiation and radiant phenomena—may not occur in the lines of force which connect particles, and consequently masses, of matter together—a notion which, as far as it is admitted, will dispense with the æther, which, in another view, is supposed to be the medium in which these vibrations take place.
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Another consideration bearing conjointly on the hypothetical view, both of matter and radiation, arises from the comparison of the velocities with which the radiant action and certain powers of matter are transmitted. The velocity of light through space is about 190,000 miles[49] a second. The velocity of electricity is, by the experiments of Wheatstone, shown to be as great as this, if not greater. The light is supposed to be transmitted by vibrations through an æther which is, so to speak, destitute of gravitation, but infinite in elasticity; the electricity is transmitted through a small metallic wire, and is often viewed as transmitted by vibrations also. That the electric transference depends on the forces or powers of the matter of the wire can hardly be doubted when we consider the different conductibility of the various metallic and other bodies, the means of affecting it by heat or cold, the way in which conducting bodies by combination enter into the constitution of non-conducting substances, and the contrary, and the actual existence of one elementary body (carbon) both in the conducting and non-conducting state. The power of electric conduction, being a transmission of force equal in velocity to that of light, appears to be tied up in and dependent upon the properties of the matter, and is, as it were, existent in them.
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LATERAL VIBRATIONS.
Fig. 20.
In experimental philosophy we can, by the phenomena presented, recognise various kinds of lines of force. Thus there are the lines of gravitating force, those of electrostatic induction, those of magnetic action, and others partaking of a dynamic character might be perhaps included. The lines of electric and magnetic action are by many considered as exerted through space like the lines of gravitating force. For my own part, I incline to believe that when there are intervening particles of matter—being themselves only centres of force—they take part in carrying on the force through the line, but that when there are none the line proceeds through space. Whatever the view adopted respecting them may be, we can, at all events, affect these lines of force in a manner which may be conceived as partaking of the nature of a shake or lateral vibration. For suppose two bodies, A B, distant from each other, and under mutual action,[50] and therefore connected by lines of force, and let us fix our attention upon one resultant of force having an invariable direction as regards space; if one of the bodies move in the least degree right or left, or if its power be shifted for a moment within the mass (neither of these cases being difficult to realise if A or B be either electric or magnetic bodies), then an effect equivalent to a lateral disturbance will take place in the resultant upon which we are fixing our attention, for either it will increase in force whilst the neighbouring resultants are diminishing, or it will fall in force while they are increasing.
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The view which I am so bold as to put forth considers, therefore, radiation as a high species of vibration in the lines of force which are known to connect particles, and also masses, of matter together. It endeavours to dismiss the æther, but not the vibrations. The kind of vibration which, I believe, can alone account for the wonderful, varied, and beautiful phenomena of polarisation is not the same as that which occurs on the surface of disturbed water or the waves of sound in gases or liquids, for the vibrations in these cases are direct, or to and from the centre of action, whereas the former are lateral. It seems to me that the resultant of two or more lines of force is in an apt condition for that action, which may be considered as equivalent to a lateral vibration; whereas a uniform medium like the æther does not appear apt, or more apt than air or water.