534: 



PHYSICS, PROGRESS OF, IN 1901. 



rays is very feeble, while fluorescence is bright. 

 Phosphorescence accompanies oxidation, hydra- 

 tion, and dehydration. Jn living beings there is 

 probably hydration and dehydration. In radio- 

 active bodies phosphorescence is readily lost by 

 hydration and by heat, which points to chemical 

 "reactions rather than to atomic properties as the 

 cause. Perfectly pure substances are not phos- 

 phorescent; traces of other substances are neces- 

 sary. Sulphide of strontium, for example, needs 

 one part per 10,000 of a salt of manganese or 

 bismuth. Phosphorescence of living beings is 

 practically universal in deep-sea life. The phe- 

 nomenon survives the life of the animal, but 

 deprivation of air and moisture stops it. It is 

 apparently due to chemical reactions. Fluores- 

 cence is explicable on principles of resonance, but 

 protracted phosphorescence, visible and invisible, 

 seems hardly so. It seems to be due to chemical 

 reactions going on even within the solid, and yet 

 extremely mobile, so that they can be set up or 

 arrested in fractions of a second, and reversible, 

 but also dependent upon the temperature, so that 

 the combination is promptly broken up by a very 

 high temperature, slowly by a lower, and not at 

 all at a sufficiently low, temperature. This points 

 toward a new field in chemistry. H. Becquerel 

 (Comptes Rendus, July 22), in observations on 

 uranium radiation at very low temperatures, finds 

 no alteration in the amount of radiation emitted, 

 even at the temperature of liquid air. The writer 

 has verified Dewar's experiment, in which, when 

 a crystal of nitrate of uranium is plunged in 

 liquid air, it becomes luminous spontaneously, and 

 believes that Prof. Dewar is correct in attributing 

 this to electrical action provoked by a molecular 

 contraction. Rutherford and McClung (Philo- 

 sophical Transactions, Feb. 27), in a discussion 

 of the energy of Becquerel rays, note that radium 

 and polonium vary very much from sample to 

 sample, both in intensity and in kind of radiation, 

 while uranium seems constant. Probably the 

 radio-activity of uranium is possessed by the 

 whole mass of the substance. In ten million 

 years each gramme of uranium in pitchblende 

 must have radiated at least 300,000 calories, and 

 radium far more. To consider these substances 

 as transformers of energy leads to many difficul- 

 ties. Possibly the regrouping of the components 

 of a molecule might explain the supply of energy, 

 but hardly in the case of radium, should it prove 

 to be persistent in its radio-activity. 



Electricity. Electrification. W. C. Henderson 

 (Philosophical Magazine, 50, November, 1900) de- 

 scribes experiments to determine whether a liquid 

 when electrified loses any of its charge by evap- 

 oration. The loss of charge from an insulated 

 vessel was found to be the same whether the ves- 

 sel was empty or contained a liquid. Experiments 

 were made with cool water, hot water, and ether, 

 and in each case the result showed no loss of 

 charge by evaporation. These results are in op- 

 position to the recently published observations 

 of Pellat. 



Conduction. E. Griineisen (Annalen der Phys- 

 ik, September, 1900) finds that the addition of 

 foreign substances reduces electric conductivity 

 to a greater extent than it does thermal con- 

 ductivity. This is specially evident in iron. F. 

 Streintz (Annalen der Physik, September, 1900)' 

 has made some experiments on powdered con- 

 ductors which indicate something like a transition 

 from metallic to electrolytic conduction. He pre- 

 pared fine powders of platinum black, graphite, 

 and lampblack, and subjected them to consider- 

 able pressure in a hole bored in a block of ebonite. 

 Judged by the temperature coefficient of the re- 



sistance, lampblack thus prepared is equivalent 

 to a dilute solution of sulfuric acid, while graph- 

 ite ranges itself among the metals. V. Cremieu 

 (Comptes Rendus, May 0) follows up his experi- 

 ments showing that electric convection produces 

 no magnetic effect by an attempt to show that 

 '"' open currents " exist, as they must if his earlier 

 experiments are correct. (See Convection, below.) 



Resistance. H. Chevallier (Comptes Rendus, 

 Dec. 24, 1900), who has previously determined 

 tiie permanent changes produced in platinum- 

 silver wire under the influence of temperature, 

 especially the change in its electrical resistance, 

 has conducted experiments which show that os- 

 cillating temperatures produce a greater change 

 in the resistance than steady temperatures. The 

 author concludes that the permanent modifica- 

 tions in the body itself are mostly due to small 

 oscillations of temperature. J. Patterson (Cam- 

 bridge Philosophical Society, April 22) has inves- 

 tigated further the facts, discovered by Longden, 

 that the resistance of thin metallic films, depos- 

 ited on glass by the cathode discharge, is much 

 greater than that calculated from the ordinary 

 specific resistance of the metal. The -author tries 

 the effect of a magnetic field upon the resistance 

 of such films, and finds that for bismuth the 

 change of resistance in the field is a small in- 

 crease, but very much smaller than that for the 

 same metal in the form of wire. The change of 

 resistance decreases with decrease in the thickness 

 of the film. 



Coherence. T. Mizuno (Philosophical Maga- 

 zine, November, 1900) states that the results of 

 experiment tend to show that the action of the 

 coherer depends in some way on the microscopic 

 sparks produced in fine metallic particles by elec- 

 tric waves, giving rise to a " welding " action that 

 forms conducting chains of particles and lessens 

 resistance. From a series of experiments on met- 

 als, alloys, and their mixtures, the author draws 

 the following conclusions: (1) In platinum, lead, 

 nickel, aluminum, cadmium, copper, steel, silver, 

 and potassium coherers the action of electric 

 waves is to reduce resistance at first largely and 

 then irregularly, and the resistance finally as- 

 sumes a fixed value. (2) With iron, tin, bismuth, 

 zinc, and antimony coherers, the resistances are 

 diminished at first, but soon afterward the 

 changes become very irregular. (3) With one 

 and also two small lead-ball coherers the resist- 

 ance attains its final value very rapidly. (4) In 

 the alloys the general tendency is to the reduction 

 of resistance to limiting values, with more or less 

 irregularity. (5) With coherers formed of mixed 

 metals, the change of resistance seems to be chief- 

 ly governed by the percentage ratios of the con- 

 stituents. (6) With zinc, lead, potassium, and 

 electric fuse, the resistance suddenly assumes in- 

 finite value at a certain stage during the experi- 

 ment. The results appear to support the view 

 that the action may be due to something like 

 welding. The lower the melting-point the greater^ 

 is the reduction of resistance. G. Ferriti (Eclair* 

 filectrique, Sept. 29, 1900) has experimented with 

 coherers of carbon-carbon, carbon-metal, metal- 

 metal, metal-liquid, in air, oil, and vacuum re- 

 spectively. The results with metals were always 

 better than with carbon. In general, the most 

 effective coherer has a resistance of 1,000 to 25,000 

 ohms, and works with a current less than a 

 milliampere. If the initial resistance is too high, 

 ihe effects are feeble and generally disappear; 

 if too low, the effects at first may be striking, 

 but they may suddenly cease. If the initial resist- 

 ance is infinite, the action is irregular; the strong 

 impulse necessary for coherence will probably 



