422 



NATURE 



[December 12, 1912 



solar radiation for its maintenance — a suggestion due 

 to Ileaviside. This, in conjunction with refraction 

 due to a gradient of ionisation, enables many pheno- 

 mena to be explained without appealing either to 

 diffraction or to absorption in the air or by the earth's 

 surface. 



Prof. A. E. Kennelly (of Harvard University) 

 pointed out that partially quantitative observations 

 on the effect of sunrise and sunset on signals received 

 near Boston from the Marconi station at Glace Bay, 

 N.S., indicated that an influence on received signals 

 was projected ahead of the sunrise at the sending 

 station. The effects might be partially explained if 

 the ionisation of sunlight in the upper atmosphere 

 produced a wall or nearly vertical series of ionised 

 strata at the boundary of the daylight illumination 

 with absorption in those strata and some irregular 

 reflection from their faces. 



Lord Rayleigh thought that there would always be 

 many difficulties so long as we considered the earth 

 a perfect conductor and the air a dielectric. Some 

 seemed to suppose that the following of a wave round 

 the earth was a consequence of the normality of the 

 wave to the surface. That this is not so can be seen 

 at once by realising that the same condition holds in 

 the case of a sound wave. 



The Sommerfeld theory was probably mathematic- 

 ally right, but a lot of time would be required to 

 form an opinion as to its applicability to the problem. 

 Sommerfeld came to the conclusion that it is the 

 imperfection in the conductivity of the earth which 

 facilitates transmission. This is certainly not in 

 accordance with the first ideas we would come to. 

 He approved of the lines of Dr. Eccles's investigation, 

 especially in connection with the day and night com- 

 plications. He was specially interested in the differ- 

 ence found to be necessary between the sending and 

 receiving antennae. This seemed to be in contradic- 

 tion to the well-known principle of reciprocity. The 

 explanation may be that for the validity of this 

 principle all the effects must be linear. It is worth 

 while to consider this difference between the two ends. 



Prof. Macdonald and Dr. Nicholson both empha- 

 sised the certainty of results calculated on the pure 

 diffraction theory, and the insufficiency of that theory, 

 and expressed approval of investigations on the lines 

 which Dr. Eccles took. Dr. Nicholson considered 

 Prof. Sommerfeld 's work to be rigorous so far as it 

 went, but it was not certain that the investigation 

 for a flat interface would apply to the earth. A 

 very small area on the earth's surface would corre- 

 spond to a very large area on a plane if one solution 

 were mathematically transformed into the other. 



Prof. A. G. Webster emphasised the importance of 

 the lack of homogeneity of the earth and air. Captain 

 Sankey seemed to despair of recording instruments, 

 because they record everything. Prof. S. P. 

 Thompson directed renewed attention to the pioneer 

 work of Sir Oliver Lodge in 1894. Mr. S. G. Biown 

 mentioned some experiments of his own in iSqg. 

 Contributions to the discussion were also made by 

 Prof. Howe, Major Squire, and Prof. F. Baily. In 

 a communicated contribution to the discussion. Prof. 

 .'\. Sommerfeld emphasised the importance of the 

 surface-waves. He thought that the difference 

 between the day and night effect was due either to 

 the increase of the conductivity of the air or to the 

 upward bending action supposed by Dr. Fleming. 

 He thought that one could not at the same time 

 consider the ionisation a satisfactory explanation of 

 the bending of the waves round the earth in long- 

 distance transmission. 



One important outcome of the discussion is that a 

 committee of the .Association has been formed to deal 



NO. 2250, VOL. 90] 



with radio-telegraphic investigations. The committee 

 is without any specific instructions, but its first inquiry 

 will probably be as to what concerted action is possible 

 between investigators on this important subject. 



General Physics. 



Prof. S. P. Thompson gave a simple demonstration 

 of the varying depth of the extraordinary image 

 formed by a cleave of unaxial crystal. A block of 

 Iceland spar was rotated so that the entrance and 

 exit faces remained in fixed planes. Of the two 

 images of a small electric light seen through this 

 block, the ordinary image remains 'fi.xed ; the extra- 

 ordinary revolves round it in a tortuous curve. 



Lord Rayleigh described some iridescent effects 

 produced by a surface film on glass. These were 

 specially brilliant when the glass was immersed in 

 water, owing to equalisation of the amount of light 

 reflected from the two surfaces. With regard to 

 methods of cleaning, Prof. Webster inquired whether 

 he had tried the well-known use of a gelatine film 

 for removing all traces of dirt. 



Prof. E. G. Coker described experiments on the 

 flow of mercury in small steel tubes, especially at 

 high velocities, at which the flow may be turbulent. 

 The lowest velocity at w-hich turbulent motion may 

 commence is found to vary inversely as the diameter 

 of the pipe and directly as the viscosity. 



Dr. J. Gray gave several exhibitions of some spin- 

 ning tops, many of them of new design, which 

 appeared very useful for exhibiting gyrostatic proper- 

 ties. 



Prof. W. Peddle described an apparatus for in- 

 vestigating the motion in torsional oscillations when 

 viscous and hysteretic effects are present. The ap- 

 paratus enabled a determination to be made of the 

 connection between displacement and time throughput 

 the motion. The author discussed the theoretical char- 

 acter of the results obtained. 



Dr. S. R. Milner read an interesting paper on the 

 current-potential curves of the oscillating spark. Two 

 induction coils connected in series were actuated by 

 the same mercury break ; one of these charged a 

 Leyden jar battery and produced the spark, the other 

 simultaneously discharged through a vacuum tube 

 giving kathode rays w-hich were deviated in two direc- 

 tions at right angles by the magrnetic field of the 

 spark current and the electric field of the spark 

 potential-difference. Photographs of the resultant 

 curves due to single sparks were shown. 



Dr. W. F. G. Swann described experiments indi- 

 cating that the conductivity of paraffin wax increases 

 with the field when values up to 100,000 volts per 

 centimetre are employed. 



Prof. W. G. Duffield and Mr. G. E. Collis ex- 

 hibited photographs of a deposit upon the poles of 

 an iron arc burning in air. The deposit, which is of 

 a feathery nature, appears to be an oxide of iron. 

 These gfrowths vary from a millimetre to a centi- 

 metre in length; they increase in size by the con- 

 densation of metallic vapour or the vapour of an oxide 

 of iron. 



A paper by Dr. G. E. Gibson on a new method of 

 determining vapour densities was taken as read in 

 the absence of the author. The quartz manometer 

 employed consists of a bulb of less than i c.c. capacity 

 blown on a quartz tube .^ mm. in diameter, and flat- 

 tened at one end so as to form a flexible membrane 

 t/io mm. thick. The interior of this membrane is 

 filled with the vapour under investigation, while the 

 exterior is enclosed in a quartz chamber which com- 

 municates with a mercury manometer. A distortion 

 of the membrane caused by a difference in pressure 

 between the interior and the exterior causes a small 



