November 29, 191 7] 



NATURE 



251 



pares the Ordnance Survey map of "Bourne Mouth" 

 in 181 1 with that issued in 1893. The present geo- 

 logical map, with its colouring of the plateau gravels 

 if Winton and Boscombe, and of the Bagshot Sands 

 if Parkstone, affords a good explanation of the human 

 development of the district. 



Accompanying the main coal seams in some parts 

 f England are often found seams of inferior coal sub- 

 ances. These frequently resemble cannel coal more 

 1 less closely, and are distinguished by giving a large 

 roportion of a very voluminous ash, making them use- 

 ss for ordinary fuel purposes. In some districts the 

 irbonaceous portion, considered apart from the ash, 

 - comparable in composition with that of a good coal, 

 ^o that the substance contains a large amount of poten- 

 tial energy, which is at present wasted. Experiments 

 have therefore been made in order to ascertain whether 

 by low-temperature distillation of the waste coal any 

 portion of this potential energy can be made available 

 in the form of oil fuel or other valuable products. 

 An account of these experiments is given by Mr. T. F. 

 Winmill in the Journal of the Society of Chemical In- 

 dustry for August 31. The main bulk of the liquid 

 products obtained was a hydrocarbon oil of a new type, 

 having a specific gravity of from 0794 to 0910, and 

 boiling between the range 150° to 360° C ; it proves 

 to be a mixture of unsaturated and polymethylene 

 hydrocarbons. The only obvious use for the mixture 

 is as a fuel oil. Unfortunately the experiments indi- 

 cated that treatment of the coal as described would not 

 in present circumstances be a commercially profitable 

 process, the cheapness of the waste coal being more 

 than offset bv the fact that no residue of saleable coke 

 is left. 



In a paper which appears in the Proceedings of the 

 Royal Society of Edinburgh for the session 1916-17 

 Dr. John Aitken gives an account of his investigation 

 of the nature of the nuclei present in air on which 

 condensation of moisture occurs when the air is 

 slightly supersaturated. The supersaturation is pro- 

 duced in the usual way by the expansion of the air 

 by amounts which, in Dr. Aitken 's apparatus, were 

 2, 4, 6, or 8 per cent. The smallest expansion causes 

 condensation on the largest nuclei, and it is repeated 

 until no further condensation occurs. Expansions of 

 4 per cent, then bring down smaller nuclei, and finally 

 expansions of 8 per cent, bring down the smallest in- 

 vestigated by Dr. Aitken. All are much larger than 

 the '■ small ions " recfuiring expansions of 25 per cent, 

 to bring them down. Pure air has fewer nuclei of 

 ■all kinds than polluted air, which, when freshly pol- 

 luted by combustion or some other chemical process, 

 has a great number of large nuclei, removable by a 

 2 per cent, expansion, and many requiring expansions 

 up to 8 per cent. The smaller nuclei disappear faster 

 than the larger. Many substances give off nuclei at 

 ordinary temperatures,' but heating facilitates the pro- 

 cess, especially if chemical action occurs. Dr. Aitken 

 takes exception to the use of the term ions for these 

 nuclei, even when they are electrically charged. 



Several aeronautical articles appear in the issue of 

 the Scientific American for October 6. .One article 

 deals with the training of airmen in the States, and 

 lays special emphasis upon the importance of the tech- 

 nical instruction which the men receive, enabling them 

 to understand every detail of the mechanical equipment 

 of their machines. A complete report is given of 

 Capt. Hucks's paper on "A Further Three Years' 

 Flying Experience" — noted recently in these columns. 

 An article on "The Classification of Military Aero- 

 planes " is of some interest, but most of its contents 

 is well known to those who follow aeronautical pro- 

 NO. 2509, VOL. 100] 



gress in this country. A short note on the use of kite 

 balloons deserves comment, as these invaluable aids to 

 artillery are seldom mentioned in our periodicals. 

 Their greatest advantage lies in the fact that they are 

 in direct telephonic communication with the battery 

 for which they are '' spotting," as the Scientific Amer- 

 ican duly points out. An excellent plate is given 

 illustrating the leading types of German aeroplanes 

 for 19 17, together with a table giving their main 

 dimensions, armament, and engine power. Among 

 the shorter articles is one which informs us that 

 America's first "Blimp" is now in commission. 

 Another short note discusses the advantages of the 

 tractor-pusher type of battleplane, a design in which 

 a small car is mounted in front of the airscrew of a 

 tractor machine, giving the gunner an excellent field 

 of fire. This idea is not new, but has not hitherto 

 met with much approval on account of the mechanical 

 difficulties of supporting the forward car. 



Engineering for November 23 contains an illustrated 

 article on the armament of aeroplanes, in which refer- 

 ence is made to the arrangements whereby a machine- 

 gun can be fired through the propeller. The German 

 Fokker of 1915-16 had a fixed quick-firing gun mounted 

 in this way, and combined with the engine, so that 

 its firing synchronised with the working of the engine. 

 This method has been adopted on most of the French 

 and enemy machines. Illustrations of a Parabellum 

 gun and also of a Maxim gun with the synchronising 

 device attached are given in the article. The ammuni- 

 tion used by the Germans is also illustrated ; the belt 

 contains ordinary, perforating, incendiary, and explo- 

 sive bullets. The incendiary bullets are hollow and 

 filled with an incendiary material, the basis of which is 

 phosphorus ; these bullets produce a trail of light, the 

 object of which is to fire airships and petrol tanks, and 

 also to enable the gunner to correct his range. The 

 perforating bullets consist of a hardened steel core 

 surrounded by a German-silver cover. The belts con- 

 tain about 10 or 15 per cent, of explosive bullets, the 

 action of which is that of small explosive shells. 



Since 1906, when Mr. Palin Elderton's useful volume 

 on "Frequency Curves and Correlation" was pub- 

 lished, many further advances have been made in 

 statistical method, and the author has now issued an 

 addendum (C. and E. Layton, 19 17) with the idea of 

 bringing the book up to date. The first part deals 

 with the exceptional types of frequency-distribution 

 derivable from Prof. Karl Pearson's differential equa- 

 tion, and the second and third parts describe brieflv 

 the calculation of a coefficient of correlation for a two- 

 rowed table by Prof. Pearson's method and the cor- 

 relation-ratio respectively. The pamphlet should be 

 in the possession of all owners of the original work, 

 a list of errata in which is also given. We have also 

 received a reprint of a short paper on the coefficient 

 of correlation by Mr. W. G. Reed, of the U.S. Weather 

 Bureau, from the Quarterly Publications of the Amer- 

 ican Statistical Association. The paper gives illustra- 

 tions of the calculation of the coefficient, and a biblio- 

 graphy of the literature. One illustration seems a 

 little misleading, though it is given as a warning. The 

 correlation between the phase of the moon and the 

 height of high-wate/ is found to be near zero. But the 

 phase of the moon is measured by the number of days 

 after full moon ; if it were expressed as a periodic 

 function the correlation would be high. 



Mr. V. C. Shippee contributes to the Chemical News 

 for November 2 an interesting note on pure sodium 

 chloride. A specimen prepared by dissolving metallic 

 sodium in distilled water, neutralising with pure hydro- 

 chloric acid, and precipitating with hydrogen chloride 



