An important discovery of a new mineral has been made in Ceylon by Prof. W. R. Dunstan in the course of a mineral survey. The discovery, which has been named thorianite, is richly impregnated with the rare earth thoria, the proportion being approximately 75 per cent. What is of commercial importance, however, is the fact that the mineral is not combined with silica. In a paper recently read before the Acad mie des Sciences, M. Victor Cremieu describes a series of researches upon liquid drops suspended in a mass of liquid of the same density, with which they do not mix. The drops are thus free from the action of gravity and their mutual attraction is counterbalanced by the pressure of the liquid. If the distance which separates the drops is considerable with relation to their diameter, the capillary forces are quite negligible. Nevertheless, he observed that the drops approached each other slowly, whatever might be the ratio of their diameter and distance apart. In the present experiments he operated with a mass of liquid kept at a constant temperature and free from all disturbances. The liquid was a mixture of distilled water and alcohol, and the drops were formed of pure olive oil. The mixture, which has the same density as the oil, is placed in a vessel four inches high and six inches in diameter, covered with a glass plate. The oil drops are introduced by means of a capillary tube. The jar is surrounded by a metal cylinder to protect it from radiation from the observer, and the vertical and horizontal movement of the drops is observed by means of slits in the cylinder. It is found that the drop always rises in the liquid, as it is impossible to have an exact equality of the density, and a very slight chemical change also occurs which modifies the initial density. With a single drop, it is found that it always rises in a straight line, starting from any point in the vessel. But with two drops the effect is different. The drops were from one to five millimeters in diameter and placed twenty-five millimeters from the sides. They were one hundred millimeters apart at first. Two hours' readings were made of their position, and it was found that they rise in a slight curve, so as to approach each other. Adding a third drop causes a deviation in that direction, and the latter also rises in a curve. These experiments are difficult to carry out, and only six observations were obtained in two months, but they gave very constant results. The author is now studying the effect of solids suspended in a liquid in the same way. M. Le Roux has carefully studied low temperatures upon phosphorescence, using liquid air. Some previous researches show that the phosphorescence is weakened or extinguished at low temperatures. In the present case he uses a light blue calcium sulphide whose light varies with the temperature when at about the heat of the human body. He places the sulphide in small sealed tubes and excites them together by magnesium light. When one of the tubes is placed in liquid air the phosphorescence is completely extinguished. On taking out the tube the light returns at the end of a few seconds, and its intensity has a maximum value when the tube comes back to the temperature of the air. It appears somewhat higher than that of the check tube according as the cooled tube has remained more or less in extinction. This is explained at once by the hypothesis that the cooling only suspends the phosphorescence, without destroying it, even partially. The phosphorescence is preserved in the potential form. Therefore when the tube returns to the same temperature as the check tube, it is brighter, since it resumes its former value, while the check tube has already weakened. A second question may be asked. When the body is initially at a temperature where the luminous energy which it acquired would become continually latent, may it acquire such energy in the latent form alone? The experiments show that such is the case. A tube of sulphide, made inactive by placing it for a long time in the dark, was plunged in a bath of liquid air while still deprived of light. The whole was taken into the light and together with a check tube was excited by magnesium light. On bringing it again into the dark room, the immersed tube showed no light, as might be expected, but when taken out of the bath and allowed to heat, it became luminous and brighter than the check tube as before. It is to be remarked that the acquired luminous potential energy has always been the maximum which the light could produce upon the body. The conclusion may be reached that the maximum luminous potential energy which a given light can give to a certain body is independent of the temperature. The temperature factor only has an influence upon the speed of transformation of the potential luminous energy into actual luminous energy. A weighing machine, said to be the most powerful in the world, is being made in Birmingham. It is capable of registering a load of 220 tons.
This article was originally published with the title "Science Notes" in SA Supplements 59, 1525supp, 239 (March 1905)