5M 



NA TURE 



[March 29, 1900 



their secret societies, their educational systems, their 

 army, their monetary systems, postal arrangements, 

 banks, theatres, and public institutions generally. This 

 book is a traveller's account of the country, with no pre- 

 tensions to be regarded as scientific ; indeed, in reading 

 the book with a view to matters of direct scientific 

 interest, we have found nothing more noteworthy from 

 this aspect than the description of the Chinese methods 

 of performing calculations and of teaching arithmetic in 

 schools. In connection with Japan, attention is called to 

 the serious competition on the part of the Japanese, 

 which threatens to undermine European commerce in 

 the East ; and the translator, as president of an Associ- 

 ation for trading with the East, corroborates this view. 



Europeans have been engaged by Japanese firms to 

 teach them European methods of manufacture, and 

 Japan is now sending out goods precisely similar to those 

 of European make, and with the trade marks copied on 

 them, and is able to sell them at lower prices than the 

 Germans. It is particularly in the competition to supply 

 the Chinese markets that Japan seems likely to outstrip 

 Germany most effectually. 



Practical Chemistry. Part i. By William French, M.A., 



F.I.C. Pp. xvi + 136. (London: Methuen and Co., 



1900.) 

 An Introduction to Qualitative Analysis. By H. P. 



Highton, M.A. Pp. xii + 170. (London: Rivingtons, 



1900.) 

 The many excellent elementary text-books now available 

 for students of chemistry ought to have a very distinct 

 influence upon chemical teaching in schools. The two 

 books under notice differ in several respects, but each is 

 the work of a teacher who knows the capacity of a school 

 curriculum for science, and the limitations as well as the 

 capabilities of the human boy. Mr. French's book 

 follows more or less closely the chemical subjects in- 

 cluded in the syllabus of elementary physics and chemis- 

 try prescribed for Evening Continuation Schools. The 

 syllabus is a reasonable one, and* therefore it has been 

 possible to describe a course of work which will meet 

 with the approval of the advocates of rational methods of 

 instruction in chemistry. Intelligent work in experimental 

 science is now encouraged by the authorities of the 

 University Local Examinations as well as the Education 

 Department ; and Mr. French's book provides a course 

 of instruction which may be adopted with advantage, not 

 only by teachers who have the requirements of examiners 

 and inspectors in view, but who desire also to cultivate 

 habits of observation and reasoning in their pupils. 



Mr. Highton's book contains a carefully graduated 

 course of practical chemistry which will serve as an 

 introduction to simple qualitative analysis. It is not so 

 distinctly a product of the "heuristic" movement as Mr. 

 French's book, and is largely devoted to systematic 

 analysis. The first part contams simple qualitative ex- 

 periments and preparations leading up to analysis ; while 

 the second comprises all the metals and acid radicals 

 not included in Part i.,and met with in simple qualitative 

 analysis. The third part deals with the separation and 

 identification of the separate parts of a mixture of two or 

 more simple salts. After a pupil has been taught to 

 think, a course of practical chemistry such as this may 

 be intelligently performed ; but if he is introduced to 

 chemistry by reagents and precipitates, the educational 

 value of his work will be very small. Mr. Highton has suc- 

 ceeded in rnaking a useful course of analytical work for 

 boys preparing for examinations in practical chemistry. 

 Essai de Chronologic des Temps prehistoriques. By M. 



Roisel. Pp. 60. (Paris : Felix Alcan, 1900.) 

 An essay in which evidence for three glacial epochs is 

 made the basis of a division of the Quaternary period 

 into seven distinct ages, extending from the year 88,000 

 B.C. to 6500 A.D. 



NO, 1587, VOL. 61] 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of rejected 

 manuscripts intended for this or any other part of Nature, 

 No notice is taken of anonymous communications. ] 



Atmospheric Electricity. 



From a paragraph in the "Notes" in Nature of March i (vol. 

 Ixi. p. 422), it will be seen that the theory advanced by Mr. 

 C. T. R. Wilson, of the Cavendish Laboratory, Cambridge, and 

 recently supported by Elster and Geitel, of the origin of atmo- 

 spheric electricity is gradually crystallising and becoming accepted, 

 as might be expected when supported by such authorities. This 

 theory is founded on the very beautiful and interesting experi- 

 ments of these investigators, which show that there are ions in 

 our atmosphere, and that these ions can form nuclei for the con- 

 densation of water vapour ; and, further, that the negative ions 

 become centres of condensation with a less degree of super- 

 -saturation than the positive ones, and consequently during con- 

 densation they will be the first to be carried down by precipi- 

 tation, the positive ions being left in the atmosphere. 



Before meteorologists accept this explanation of atmospheric 

 electricity there are some points I would like to place before 

 them for their consideration. These ions do not act as centres 

 of condensation unless the air be highly supersaturated, whilst 

 dust particles are active in saturated air, and some of them in air 

 that is not quite saturated. So that before we can accept this 

 theory of the electrification of the air we must be sure there is 

 such a thing as dust-free air in our atmosphere ; because if there 

 is not there can be no such thing as the supersaturated air 

 required to produce this separation of positive and negative ions. 



Mr. Wilson is evidently conscious of this difficulty (Phil. 

 Trans, vol. cxciii. pp. 289-308), as he adds a note to the end 

 of his paper, in which he states that there is no evidence of 

 supersaturation in the atmosphere ; but he also says there is an 

 equal lack of evidence against its existence ; and whilst admitting 

 it cannot exist in the lower dust-charged layers of the atmosphere, 

 he is reluctant to give up the theory on that account, and 

 supposes it may be possible that cloudy air may be purified of its 

 dust as it ascends, by the dust particles becoming weighted by 

 the vapour condensed on them, when they will fall, or the air 

 may rise up through them and be dust-free when it escapes. 

 Now any one who has been in clouds, or knows the slow rate at 

 which cloud particles descend, will be aware that this process is 

 an extremely slow one, and compared with movements of the 

 cloud as a whole very insignificant. But suppose we give the 

 cloud every chance to get free from its cloud particles : let it be 

 kept quite still and free from eddies, and time allowed for all 

 the water particles to fall out of it. Now what would be the 

 condition of the air afterwards ? Practically what it was before 

 the cloud was formed. There would be a smaller number of 

 dust particles in the air, but there would still be plenty to form 

 a number of clouds in succession if the vapour supply was not 

 exhausted. When a cloud forms in ordinary impure air, only a 

 small proportion of the dust particles become active centres of 

 condensation, whilst many receive no charge of vapour. On the 

 Rigi Kulm {Trans. Roy. Soc. Edin. vol. xxxvii. Part iii. 

 No. 28) I have counted as many as 3000 and 4000 dust particles 

 per c c. in clouds, and on one occasion as many as 7700 in a 

 dense cloud. Whilst in fog, which we may call a low-level 

 cloud, I have observed as many as 50,000 dust particles per c.c. 

 With thousands of dust particles in each cubic centimetre it is 

 evident a cloud has dust nuclei sufficient for making a number of 

 clouds should the first formed cloud particles be precipitated, as 

 these dust particles will move with the air, whilst the cloud 

 particles fall out. 



No doubt clouds do not always have such large numbers o. 

 dust particles in them as the clouds above referred to, but 

 cumulus clouds seem to be always pretty well supplied in that 

 way, especially over continental areas. Then, as the quantity 

 of water to be condensed is limited to the amount the cloud 

 takes up with it from the surface of the earth — as it is not 

 Hkely to have any vapour added to it unless it falls below the 

 rain cloud level — there seems generally to be enough dust 

 particles to condense all the water. 



We must further remember that nature is economical in its 

 use of these dust particles. If the cooling is taking place very 

 rapidly, a large number of particles at once become active^ 

 but after a time a number of them lose their load of water by 



