SCIENCE-GOSSIP. 



285 



CONDUCTED BY JAMES QUICK. 



Nuclei of Condensation. — Much useful work 

 has been done by Aitken and others upon the 

 essential part played by nuclei of some kind in 

 effecting condensation in the atmosphere. Still 

 the subject requires more data. Mr. C. T. R. 

 Wilson, in a paper read recently before the Royal 

 Society, takes up the matter and discusses the 

 relative efficiency of the Rontgen and the 

 Uranium rays, as well as of electrical discharges 

 from points, in producing condensation. It is 

 found that the nuclei from these rays require 

 about the same expansion of the air to bring the 

 latter to supersaturation point. In the case of 

 moist air exposed to ultra-violet light, and when 

 the radiation is weak, the nuclei require as great a 

 degree of supersaturation as the above. If the 

 radiation is stronger, however, these nuclei appear 

 to grow, and the expansion required for condensa- 

 tion then depends on the intensity of the ultra- 

 violet light and on the time for which the gas has 

 been exposed to the rays before expansion. 



New Influence Electrical Machine. — An 

 interesting new form of influence electrical machine 

 was described recently before the Physical Society, 

 by Mr. W. R. Pidgeon. As regards the rotating 

 discs and earthing arrangements, it is similar to a 

 Wimshurst machine. Each sector, however, is 

 embedded in an insulator, and only the brass knob 

 projects. The sectors receive their charge at a 

 moment when they stand between charged inductors 

 and when their capacity is at a maximum. Each 

 sector carries forward a double charge as compared 

 with that carried forward by a machine without 

 inductors. 



British Association Meeting at Dover. — 

 The Bristol meeting of the British Association in 

 September last was one of the most successful 

 held for a considerable number of years. This 

 year's meeting at Dover, although perhaps the 

 town and neighbourhood do not offer quite the 

 same scientific attractions as Bristol, should prove 

 quite as interesting. The meeting of the French 

 Association is arranged to be held contemporane- 

 ously at Boulogne, and the two bodies will 

 exchange visits. A statue of the poet Campbell 

 •will be inaugurated while the members of the 

 British Association are at Boulogne, and Dr. Chas. 

 Richet, Professor of Physiology in the University 

 of Paris, has consented to deliver one of the 

 evening discourses at Dover. 



Specific Resistance of Steels. — An interesting 

 paper, by H. Le Chatelier, dealing with the varia- 

 tion in the specific resistances of specimens of steel, 

 has appeared in " Comptes Rendus." His results 

 ■show that the resistance increases with the amount 

 of carbon ; the average increase being seven mi- 

 crohms for one per cent, of carbon by weight. The 

 resistance also increases with both silicon and 

 manganese. With the former about seven mi- 

 crohms for one per cent, increase, and with the 

 latter about five microhms. 



The Zeeman Effect. — At the beginning of 

 1897, Dr. Zeeman reported his observations 

 upon the effect produced upon a source of light 

 when placed in a strong magnetic field. The 

 spectral lines emitted by that source of light are 

 modified according to the direction in which 

 they are seen through the spectroscope. When 

 the light is viewed with the slit of the spec- 

 troscope across the lines of magnetic force, each 

 spectral line is split up into a triplet. More- 

 over, these three lines are plane polarized. When 

 the light is viewed along the lines of force, the 

 original spectral line becomes a doublet, and these 

 are circularly polarized. 



Regarding the Zeeman effect, Professor Fitz- 

 gerald points out that the converse of this should 

 exist. It is quite possible, he says, that if a 

 circularly polarized beam of sunlight were passed 

 through a strongly absorbing gas, it would 

 magnetise it to an observable extent. Professor 

 Fitzgerald is having the experiment tried, and 

 some interesting results may be looked for. 



Space-Telegraphy. — Sometimes a physicist is 

 asked : What is the practical use of so much 

 theorising upon the properties of the ether in 

 space ? But surely such a questioner has been 

 answered during the last two years. Space - 

 telegraphy has grown apace in this period, and 

 especially during 1898. December last, saw three 

 very important papers read before the Institution 

 of Electrical Engineers by three of the foremost 

 workers upon the subject: Professor Oliver J. 

 Lodge, On " Improvements in Magnetic Space- 

 Telegraphy " ; Mr. W. H. Preece, on " Etheric 

 Telegraphy"; and Mr. Evershed, on " Telegraphy 

 by Magnetic Induction." Theoretical reasoning 

 and experimental results were given in detail, the 

 result being that a general system of space signal- 

 ling looks decidedly hopeful. Considering, how- 

 ever, the amount of work that has been done and 

 is being carried on by Marconi, more reference 

 might, perhaps, have been made to him in the 

 those, papers than was done. Marconi's system 

 is capable of signalling a distance of twenty 

 to twenty-five miles. Successful work has been 

 done in England, Ireland and elsewhere, and it is 

 reported that arrangements have been sanctioned 

 by the various authorities for further trials between 

 important stations. 



Coherers. — The interest taken in the so-called 

 "Wireless Telegraphy " has produced many forms 

 of experimental coherers for receiving the wave 

 impulses, and transforming them. A sensitive 

 coherer is described by Arons in " Wiedemann's 

 Annalen." It is made by cutting a fine line across 

 a thin strip of tinfoil stuck on glass, laying a little 

 metallic powder over it, adding a drop of Canada 

 balsam, and covering it with a cover-glass. On 

 exposing such a coherer to the electric waves, full 

 contact will generally at once be produced, 

 especially when the particles are at all dense. 



There are, however, difficulties to be got over 

 in the working of coherers. Not only are they 

 affected by electrical impulses, but sound waves 

 also affect their resistance. This influence depends 

 upon the pitch of the sound. In some experiments 

 upon this point a Branly coherer, consisting of 

 copper filings, was placed in the focal line of a 

 Hertzian mirror. Of some twenty organ-pipes 

 sounded near, only one produced a deflection, but 

 this deflection was not less than that due to 

 electric waves. 



