The Terrestrial Magnetic Elements at Greenwich for the year 1913 were:—
| Declination | 15° 15.2´ west. |
| Dip | 66° 50.5´. |
| Horizontal Force | 0.1851 C.G.S. units. |
J. R. A.
Physics.
The constitution of the atom continues to be a subject of experimental inquiry. According to Sir Ernest Rutherford's views on the scattering of [Greek: a]α-rays the atom consists of a central nucleus of positive electricity around which one or more electrons revolve. Mathematicians have objected that such a system is not stable, but N. Bohr has evaded this difficulty by introducing Planck's theory of a quantum of energy, which states that energy is not emitted continuously but in discrete atomic quantities. For the simple atoms of hydrogen and helium Bohr's theory gives some remarkably accurate representations of certain properties of these elements; especially in relation to the spectral lines. Van der Broek contends that the nuclear positive charge is exactly equal to the atomic number, and certain experiments by Moseley on the x-ray spectra of the elements are regarded as confirmatory of this.
The quantum hypothesis of Professor Planck, referred to above, which regards energy as transferable in definite units and not continuously, is being applied to several physical problems with some measure of success. For example, Professor Nernst has recently investigated the specific beats of the solid elements at very low temperatures and by the application of a formula due to Debye, involving the quantum hypothesis, a very good agreement between theory and experiment is obtained. An excellent review of this work and the bearing of the quantum hypothesis on such different subjects as photo-electricity, the line spectra of the elements, and radiation generally, has been written by Mr. J. H. Jeans and published by the Physical Society of London. Mr. Jeans inclines to the view that the classical Newtonian Mechanics must be revised to meet the conditions which the quantum hypothesis have called forth.
Professor Millikan has attempted direct proof of a cardinal feature of this hypothesis, namely the direct proportionality between the frequency and the energy of radiation, by showing experimentally that the energy of the electrons ejected from metals by the action of light is proportional to the frequency of the light vibrations.
An important discovery has been made by J. Stark that hydrogen in a state of luminescence when subjected to an electric field has its spectral lines resolved into three or more components, an effect analogous to the Zeeman effect in which the spectral lines are resolved into components by the action of a magnetic field. The effect has been observed independently by Lo Surdo whilst working on the positive rays in a vacuum tube. The two outer components of an electrically resolved line are polarised at right angles to the remainder, the separation of the components being proportional to the field intensity and increasing with decreasing wave length. The electric effect is not the same in all its details as the magnetic effect and is not always quite easily interpreted, but the discovery puts a new means in the hands of the physicist for the investigation of the structure of the atom.
Messrs. Kaye and Higgins have continued their researches on the emission of electricity from substances at temperatures of 2000° to 2500° C. from which currents, generally of negative electricity, are obtained of a density as much as 1 to 2 ampères per sq. cm. Boiling brass, however, emits a positive current of 0.5 ampères per sq. cm. The subject is of considerable interest in connection with the problem of the electric and magnetic state of the sun. These experiments, however, are not altogether in agreement with Professor Richardson's view that the emission of thermions from hot bodies is a kind of evaporation of electrons following a law like that of liquid evaporation under rise of temperature.
A most interesting experiment has been carried out by Professor K. Onnes as a branch of his low temperature researches. A coil of lead was constructed and cooled to within a few degrees of absolute zero at which temperature its resistance is 2 × 10-10 of what it is at normal temperature, consequently an induced current when started persists after the inducing electromotive force is withdrawn, as there is no appreciable resistance and therefore no dissipation of energy into heat. In this way it has been possible to realise the conception of electric currents continuously circulating round atoms, which was first introduced by Ampère to account for magnetism.