The theory of light / by Thomas Preston.

  • Preston, Thomas
Date:
1901
Catalogue details

Licence: In copyright

Credit: The theory of light / by Thomas Preston. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    Similarly a supply of energy is required to maintain an electric current, and the phenomena arising from the current are manifestations of the presence of this energy in the ether around the circuit. Formerly an electrified body was supposed to have something called electricity residing upon it which caused the electrical phenomena, and an electric current was regarded as a flow of electricity travelling along the wire, while the energy which appeared at any part of the circuit (if con- sidered at all) was supposed to have been conveyed along the Avire by the current. The existence of induction, however, and electromag- netic actions betweeif bodies situated at a distance from each other, lead us to look upon the medium around the conductors as playing a very important part in the development of the phenomena. It is, in fact, the storehouse of the energy. Upon this basis Maxwell founded his theory of electricity and magnetism, and determined the distribution of the energy in the various parts of the field in terms of the electric and magnetic forces. The ether around an electrified body is charged with energy, and the electrical phenomena are manifestations of this energy, and not of an imaginary electric fluid distributed over the conductor. When we speak of the charge of an electrified conductor we refer to the charge of energy in the ether around it, and when we talk of the electric flow or current in a circuit we refer to the only flow we know of, viz. the flow of energy through the electric field into the wire. 328. Polarisation of the Ether—Electric Waves.—The work spent in producing the electrification of a conductor is spent on the ether and stored there, probably as energy of motion. To denote this we shall say that the ether around the conductor is polarised, this word being employed to denote that its state or some of its properties have been altered in some manner by the work done on it—that is, by the energy stored in it. In the case of a conductor possessing what is termed a positive charge, the ether around it is polarised in a certain manner and to a certain extent depending on the intensity of the charge. If the charge be negative the polarisation is in the opposite sense, the two being related, perhaps, like right-handed and left-handed twists or rotations. Now consider the case of a body charged alternately, positively and negatively, in rapid succession. The positive charge means a positive polarisation of the ether, which begins at the conductor and travels out through space. When 'the body is discharged the ether is once more set free and resumes its former condition. The negative charge now entails a modification of the ether or polarisation in the opposite sense. The result of alternate charges of opposite sign is that the
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