July 3, 1913] 



NATURE 



47i 



withstanding the fact that all the temperatures are 

 below the critical. — E. E. Eournier d'Albe : The 

 efficiency of, selenium as a detector of light. The 

 efficiency of a selenium preparation used as a detector 

 of light is defined as the amount of additional conduc- 

 tivity imparted to it by the unit of incident light. Since 

 many factors affect the efficiency of a given selenium 

 bridge, standard conditions are chosen, chief among 

 them being an illumination of one lux. The law of 

 light action is studied, and the total effect is shown 

 to be proportional to the square root of the incident 

 energy, while the instantaneous effect is proportional 

 to the energy. This is verified down to an illumina- 

 tion of o-ooooi metre-candle. It is shown that sele- 

 nium is the most efficient light detector known, that 

 it is capable of discriminating minute differences of 

 luminous intensity far beyond the capacity of the 

 eye, and that, with suitable means of detecting minute 

 currents, it should offer a means of testing the quanta 

 theory of light by direct experiment. — A. E. Oxley : 

 The Hall effect in liquid electrolytes. Experiments 

 have been made on aqueous solutions of copper sul- 

 phate, silver nitrate, cadmium sulphate, and on copper 

 sulphate gel. Each substance was placed in a small 

 cell of glass or mica, and was subjected to a uniform 

 magnetic field. A Paschen galvanometer was used 

 to measure the transverse potential difference. In a 

 uniform magnetic field this transverse potential differ- 

 ence is due partly to a true Hall effect (depending on 

 the difference of the ionic mobilities), and partly 

 to a concentration Hall effect (depending on 

 the sum of the ionic mobilities). The latter 

 effect is primarily the one which has been measured 

 in this research, and the former, which is smaller. 

 is included. Eight experiments have been made, and 

 the transverse potential differences, which changed 

 sign on reversal of the magnetic field, have been found 

 to agree with the calculated values. The relation be- 

 tween the transverse potential difference and the 

 intensity of the magnetic field, for an aqueous solu- 

 tion of copper sulphate, is linear.— Prof. W. B. 

 Morton : The displacements of the particles and their 

 paths in some cases of two-dimensional motion of a 

 frictionless liquid.— S. Chapman : The diurnal variations 

 of the earth's magnetism produced bv the moon and 

 «un.— Prof. H. A. Wilson and Marjorie Wilson : The 

 electric effect of rotating a magnetic insulator in a 

 magnetic field.— A. Hopwood : The magnetic materials 

 in claywares. The author has found that white, 

 cream, grey, yellow, buff, red, or brown claywares are 

 feebly or moderately magnetic owing to the presence 

 of unfused grains of unchanged ferruginous minerals 

 and fused globules of complex ferruginous silicates; 

 while flashed, brindled, or blue claywares are always 

 strongly magnetic owing to the presence of complex 

 ferruginous silicates and finelv disseminated magnetic 

 oxide of iron. The origin of the complex ferruginous 

 silicates in claywares is quite different from that of 

 the magnetic oxide of iron. While the latter is pro- 

 duced either by the orientation of the magnetite 

 originally present in the clays, or by the reducing 

 action of the kiln gases on the precipitated or colloid 

 oxides, hydroxides, or carbonates of iron disseminated 

 throughout the clays, the former are produced by the 

 fusion of the granular or concretionary ferruginous 

 minerals, i.e. iron pyrites, siderite, haematite, mag- 

 netite, biotite, &c, occurring in the clays with the 

 surrounding matrix.— A. Hopwood and C' Weizmann : 

 Synthesis of the anhvdrides of o-aminoacyl glucos- 

 amines.— H. S. Jones : The flexure of telescope mirror- 

 discs arising from their weight, and its influence upon 

 resolving power.— Prof. W. H. Young : Fourier series 

 and functions of bounded variation. In the present 

 communication it is shown that in a number of funda- 

 NO. 2279, VOL. 91] 



mental theorems the derived series of the Fourier 

 series of a function of bounded variation may take 

 the place of the Fourier series of a summable function, 

 and this even when the function of bounded variation 

 is not continuous, or still less an integral. In par- 

 ticular, the coefficients of such a series" may be used 

 as convergence factors, with result-, which approxi- 

 mate to, or are even identical with, those obtained 

 when the convergence factors are the coefficients of a 

 Fourier series. The use of these convergence factors 

 transforms, in fact, when the function of bounded 

 variation is odd, a Fourier series into a Fourier series, 

 and an allied series into a Fourier series when the 

 function of bounded variation is even. — Prof. W. H. 

 Young : A condition that a trigonometrical series 

 should have a certain form. In the present communi- 

 cation a necessary and sufficient condition that a 

 trigonometrical series should have a form in which 

 its coefficients are expressible in terms of Stieltjes 

 integrals with respect to a function of bounded varia- 

 tion is obtained. — Prof. W. H. Young : Trigono- 

 metrical series the Cesaro partial summations of which 

 oscillate finitely. 



Paris. 

 Academy of Sciences, June 2j.— M. F. Guyoii in the 

 chair. — M. d'Arsonval : Some remarks on the papers 

 read at the meeting at Toulouse of the Congres 

 national du Froid. — J. Guillaume : The present sun- 

 spot minimum. During the seventy-three davs from 

 April 12 to June 23 no spot has been noted" on the 

 sun's disc. — A. Tian : An experimental determination 

 of the light energy absorbed in a photochemical 

 reaction. A description of a null method based on 

 the use of a thermopile. In the photochemical decom- 

 position of hydrogen peroxide there is no propor- 

 tionality between chemical action and the energy 

 absorbed, even when the light used contains no infra- 

 red rays. — Jacques Carvallo : A photo-electric pheno- 

 menon presented by liquid sulphur dioxide. In a pre- 

 ceding communication it has been shown that liquid 

 sulphur dioxide submitted to a constant potential 

 difference between two platinum electrodes is 

 traversed by a current which tends to a constant limit. 

 This phenomenon is sensitive to the action of light : 

 each exposure causes a sudden decrease in the cur- 

 rent. The effects have been proved to be due to 

 ultra-violet rays. — Thaddee Peczalski : A relation be- 

 tween _ the law of compressibility of gases and the 

 coefficients of expansion. — Andre" Leaute : The high- 

 frequency oscillations in very short electric arcs. From 

 the experiments described a new position is proposed 

 for safety fuses in connection with high-tension cir- 

 cuits. — P. Th. Muller and R. Romann : The electro- 

 lytic dissociation of a salt, governed by the mass law. 

 A study of the conductivity of solutions of piperidine 

 cyanacetate. For this salt the ionisation, measured 

 by the conductivity of the solution, is governed by 

 the law of mass action. — Marcel Boll : The photo- 

 chemical decomposition of solutions of oxalic acid in 

 presence of uranyl nitrate. The electrical con- 

 ductivity measurements showed that the reaction was 

 unimolecular, the solution being illuminated with 

 monochromatic light. The energy absorbed during 

 the reaction is much lower than the quantum of 

 Einstein.— Marc Landau : The phenomenon of photo- 

 catalysis. All compounds of uranium possess marked 

 photocatalytic properties; there is no relation between, 

 the values for the photocatalytic power and the radio- 

 active power of these compounds. Catalysis takes 

 place even when the uranium compounds used as 

 catalysers are insoluble. — E. Rengade : The melting 

 points, specific heats, and heats of fusion of the 

 alkali metals. Measurements of these three constants 

 are given for sodium, potassium, rubidium, and 



