June 6, 1918] 



NATURE 



27: 



Dr. L. De Launay, in the issue of La Nature for 



May i8» describes the efforts of a French company to 

 cultivate the eucalyptus and pine on a large scale in 

 the Peiiarroya district of Spain (on the borders of 

 C6rdoba and Ciudad Real) for the production of 

 paper-pulp. At first the geological conditions of this 

 region were not considered favourable for intensive 

 afforestation, but experiment shov^ed that the two 

 woods mentioned would yield satisfactory results 

 under proper treatment. The results are justifying 

 expectations, and it is hoped that the once barren 

 region will in a few years repay the time and money 

 spent in developing it. The wood will be used for 

 pulping, pit-props (there are mines near), and for the 

 distillation of acetic acid, etc. 



From a copy we have received of Prof. Righi's paper 

 on the ionisation produced by X-rays in a magnetic 

 field, which appeared recently in the . Annales 'de 

 Physique, it is evident that the presence of a mag- 

 netic field has an influence on the process of ionisa- 

 tion of gas molecules not taken into account in 

 previous descriptions of the process. If two hori- 

 zontal plates are maintained at a difference of poten- 

 tial in a rarefied gas through which X-rays are 

 passing, and the electric current between the plates is 

 measured, we get the well-known relation between 

 the current and the applied potential. If a horizontal 

 ] magnetic field is superposed on the electric field 

 between the plates, we should expect the deflection 

 of the electrons produced by the field to diminish the 

 current between the plates. This Righi finds to be 

 the case for fields of looo gauss, but for fields of 

 300 or 400 gauss he finds the current is increased 

 slightly by the presence of the field. He ascribes J;his 

 effect to the electron placing itself so that its orbit is 

 perpendicular to the field. The force of the field on 

 it then being centrifugal, there is an increased tendency 

 for ionisation to occur in the gas. 



The British Journal of Photography in its issue of 

 May 5 directs attention to the numerous openings for 

 improvements in optical apparatus as at present con- 

 structed, and advises manufacturers to employ experts 

 to examine and improve their designs. As examples, 

 it suggests the provision of two shallow saw-cuts at 

 opposite ends of a diameter of each bezel ring used 

 in a lens mount, so that by placing the edge of a 

 steel rule in the cuts the ring can be easily removed. 

 For lantern condensers the fine threaded screw method 

 of mounting should be given up and replaced by the 

 bayonet catch, or, better, by a stiff spring ring inside 



i the mount holding the front lens against a loosely 

 fitting separating ring, which in turn holds the back 

 lens against a flange on the inside of the mount at 

 the lantern end. Holes should be provided in the 



'■■ mount to allow any condensed moisture to get away. 



? The condenser should be mounted in a-^cradle, which 

 will allow of its insertion and removal when the 

 lantern is in use without its being necessary to remove 

 the lamp and withdraw the condenser through the 

 body of the lantern, as is so often the case. 



Prof. E. W. Marchant read an interesting paper 

 on " Some Transient Phenomena in Electrical Supply 

 Systems " to the Institution of Electrical Engineers on 

 .\iay 24. The experiments were made with the help 

 of an oscillograph at the electrical station and sub- 

 stations of the Liverpool Corporation. Prof. Marchant 

 investigated the "current-rushes" on switching trans- 

 fcjrmers into the circuit. The results obtained bear 

 out the conclusions which Prof. Fleming arrived at in 

 ilie experiments he carried out twenty-five years ago 

 at the Deptford power-station of the London Electric 

 Supply Corporation, which was the first high-tension 



NO. 2536, VOL. lOll^ 



supply station in the world. Prof. Fleming's apparatus 

 was, naturally, more primitive, but with the help of 

 vacuum tubes and improvised electrical stethoscopes 

 he detected all the main phenomena. We were 

 specially interested in Prof. Marchant's oscillograms, 

 showing the rush of current which ensues when an 

 induction motor is switched into a circuit, as they 

 prove that, although the initial rush of current may- 

 be the same whether the machines be carefully syn- 

 chronised or not at the moment of switching in, yet 

 the current diminishes to its steady value much more 

 rapidly in the former case. The latter part of the 

 paper on the current-surges which occur when putting 

 alternators in parallel, and the transient currents 

 which ensue on switching on and off high-tension 

 cables, although containing little that is novel, gives 

 excellent illustrations of the substantial accuracy of 

 the ordinary differential equations used by engineers. 



OUR ASTRONOMICAL COLUMN. 



Early History ok the Solar System.— An impor- 

 tant contribution to the mathematical investigation of 

 the evolution of the solar system has been made by 

 Dr. Harold Jeffreys in a communication to the Roya'l 

 Astronomical Society (Monthly Notices, vol. Ixxviii., 

 p. 424). It is first "shown to'be improbable that the 

 planets were formed by the gradual condensation of 

 a gaseous mass, and it would seem that they were 

 strongly condensed from the beginning, and were 

 formed catastrophically. The tidal theory is therefore 

 adopted, according to. which a star of mass several 

 times greater than that of the sun approached it so 

 closely that the tidal action resulted in the extrusion 

 of one or two streams of matter having a considerable 

 velocity. These streams would break up almost at 

 once into a series of fluid masses, and the gaseous 

 matter set free in the initial disruption would form 

 a resisting medium, the effect of which would be to 

 reduce the eccentricities of the original orbits. From 

 the rate of change of eccentricity it is provisionally 

 estimated that the age of the solar system is 3 x 10* 

 years, which is in general agreement with the age 

 derived by radio-active methods. Among other results 

 of interest it is shown that all the bodies having 

 diameters less than 1000 km., if assumed to be com- 

 posed of silica, must have been liquid or solid from 

 the beginning, as smaller masses could not have been 

 held together by their own gravitation when in the 

 gaseous state. Dr. Jeffreys considers that the 

 asteroids were probably formed from a primitive planet 

 which approached Jupiter so closely as to be broken 

 up by tidal action. 



Stellar iNVEsriG.vriONs at Mount Wilson. — In the 

 Journal des Observateurs, vol. ii., No. 6, Mr. W. S. 

 .\dains gives a brief account of the more general 

 stellar investigations which have recently been carried 

 on at Mount Wilson Observatory. Following an ex- 

 planation of the spectroscopic method of determining 

 stellar parallaxes, it is stated that the method has 

 now been applied to more than a thousand stars, and 

 that the precision of the results appears to be of the 

 same order as that of parallaxes measured directly'. 

 In regard to stellar motions, space velocity appears 

 to be mainly a function of absolute magnitude, the 

 fainter stars moving more rajMdly than the brighter, 

 probably to some extent on account of difference in 

 mass, the less massive stars having the greater veloci- 

 ties. A recomputation of the constants of the solar 

 motion- gives the position of the sun's apex as R.A. 

 2709°, (feci. +292°, and velocity 2148 km. The 

 investigations of stream motion furnish considerable 

 support to the view that the stars show a motion of 

 revolution around the centre of the galaxy, and that 



