Professor Jean Perrin in a recent course of lectures has explained his striking and beautiful experiments on the movement of small particles suspended in liquids. When an emulsion of such particles is dilute the laws which are applicable to gases are obeyed, but when the emulsion is concentrated van der Waal's law for dense vapours then holds good, and in this way these important laws of the behaviour of invisible molecules can be ocularly demonstrated.
Hiromu Takagi has examined the change of magnetic properties of magnetite with rise of temperature and is unable to confirm the sudden changes of susceptibility which were said to occur at definite points above the critical temperature. These changes Professor Weiss claimed as one proof of the existence of an elementary indivisible unit of magnetism, which he named the magneton, and the evidence for this unit must therefore rest upon other experiments.
The very large intrinsic field of a magnet required by the kinetic theory of magnetism receives some confirmation by the application of an experiment, by Hurmuzescu, on the electromotive force developed in a cell consisting of two identical pieces of soft iron in dilute acetic acid, one of which is strongly magnetised. Calculation then shows that if the electromotive force arises from an intrinsic field, such a field must have a magnitude of the same order as is required by the theory.
Electrification can be produced by the splashing of water, a subject which has received a good deal of attention as it has a bearing on the origin of atmospheric electricity. Mr. J. J. Nolan has found from his experiments that the charge is of positive sign and inversely proportional to the radius of the drops, and he deduces the result that the charge is proportional to the new surface formed as the water breaks up, and that the magnitude of the charge produced per unit area of water surface is 2.7 × 10-3 electrostatic units.
An interesting example of how pure science is beneficial to industry is afforded by Professor Bone's experiments on surface combustion. It has been a popular lecture experiment for a long time past to exhibit the combination of combustible gases below the flame temperature when they are in contact with solids, and it is in this way possible to keep a solid incandescent by flameless combustion. Applying this result Professor Bone has constructed a boiler in which the water is heated by the metal tubes within it being raised to a high temperature by flameless combustion, and such a boiler has a very high efficiency. A trial on a large scale gave an efficiency of 92.7 per cent.
The work of the National Physical Laboratory has been extended to include a new department for the testing of radium preparations and for certifying the strength of radio-active preparations. This department is under the superintendence of Dr. Kaye.
The death of Professor John Henry Poynting in March last is a loss to English science. His name will always be associated with the theorem on the transference of energy in the electro-magnetic field which he was the first to enunciate.
J. R. A.