March 2, 1922] 



NATURE 



287 



tions, illumination of the actual ground, and fixed 

 illuminated signs to show the position of wind, etc. 

 At Croydon the lighting of high wireless masts, which 

 form dangerous obstructions, has been effected by 

 placing looo-c.p. gas-filled lamps, screened red, on the 

 top of the masts. These form a good recognition mark. 

 Ground illumination requires special care to avoid 

 ilazzling the eyes of pilots at some angles. A special 

 arrangement recommended at the International Air 

 Convention is the use of hghts arranged in the form 

 of two " L's " to indicate positions for " taking off " 

 and landing. Such lights were originally mounted in 



reflectors covered by flat glass discs in such a way 

 that they were reSidily visible from above, but in- 

 visible at close range. Better methods of diffusion, 

 enabling lights to be seen at all angles, have since 

 been devised. Searchlights appear helpful, but have 

 to be used with care to avoid confusing shadows when 

 the machine is near the ground. An appendix to the 

 paper contains particulars of the recommendations of 

 the International Air Convention in regard to signals 

 of distress, etc. Much has yet to be done in this new 

 field, but the paper affords a useful review of existing 

 procedure. 



The Preservation of Stone. 



A LECTURE to the Royal Society of Arts on the 

 ■^^ above subject by Mr. Noel Heaton is pubUshed 

 in the Journal of the society for December 30 last. 

 The lecturer gave an account of the various attempts 

 which have been made to solve the important problem 

 of preventing the decay and disintegration of stone- 

 work in buildings. The great majority of modem 

 stone buildings, and a still greater proportion of 

 medieval buildings, are constructed of limestone or 

 sandstone, and the problem centres around these 

 \arieties rather than about the more resistant granite, 

 used only to a limited degree. The causes of dis- 

 integration may be natural, depending on fluctuations 

 of temperature, on rain, on erosion by wind, and, in 

 ferruginous sandstones, on oxidation. Minute differ- 

 ences in structure often cause great differences in dura- 

 biUty. The growth of vegetation on stone usually 

 hastens decay. The most potent cause of decay is, 

 however, the " unnatural " action of sulphuric acid, 

 derived from coal-smoke, coupled with the accumula- 

 tion of soot and grime. Sir Frank Baines, who intro- 

 duced the lecturer, stated that, roughly, 80,000 tons of 

 sulphuric acid are thrown annually into the London 

 atmosphere. Strain set up by the rusting of iron is 

 also a contributory cause of decay. The lecturer then 

 turned to the means of preventing decay. 



An indirect method of preventing decay is to fur- 

 ther, by every possible means, the campaign against 

 atmospheric pollution. The stone may be treated 

 with preservatives, which were divided into three 

 groups : (a) those acting merely as surface coatings ; 

 (Z>) those impregnating the stone without chemical 

 action ; and (c) those operating by chemical reaction 

 with the stone. In the first class are paint and lime- 

 wash, the latter being useful where the stone is 

 subjected to a moist atmosphere, but protected from 



rain. In the second class are mineral wax applied 

 by heat or in solution in benzene, drying oils, creosote, 

 or gelatinous precipitates formed on the stone. The 

 first process is very old, and is effective for certain 

 purposes. Treatment with alum solution, followed 

 by soft soap, which results in the precipitation of an 

 aluminium salt of the fatty acids, is recommended. 



In the third class treatment with baryta is effective 

 in repairing a stone disintegrated by sulphuric acid. 

 A common method is the deposition of silica or siU- 

 cates. Treatment with waterglass leads to unsightly 

 efflorescence. This may be reduced by treating with 

 a solution of arsenic acid after the waterglass, but 

 the most satisfactory results are obtained with silico- 

 fluorides, introduced in France by Kessler in 1883. 

 A solution of magnesium silicofluoride reacts with 

 limestone : 



MgSiFg +2CaC03 = SiO, +MgF2 +2CaF2 +2CO.2. 



The solution, known as " Fluate," is manufactured in 

 France, and the lecturer stated that, although the 

 results were conflicting, it appeared to be beneficial. 

 In America the double salts of magnesium and zinc 

 were preferred. The use of the solution has recently 

 been investigated by Prof. Desch, in conjunction with 

 the Department of Scientific and Industrial Research, 

 and, although the detailed results have not yet been 

 published, the conclusions appear to be that too strong 

 a solution should not be used (not stronger than 

 10 per cent.), and that the mode of application should 

 be adjusted to particular conditions. The method is 

 most useful on new work. The use of nostrums of 

 unknown composition is strongly condemned, as they 

 may cause great injury. Sir Frank Baines also con- 

 tributed some valuable information in the discussion 

 on the lecture. 



Mathematics in Japan. 



A GOOD many years ago there was an exhibition 

 -^ *■ at Earl's Court in which the Japanese Govern- 

 ment and nation took a conspicuous part. For 

 -cveral reasons the Japanese art section was par- 

 icularly interesting. It contained priceless and 

 luthentic specimens of their national painting and 

 luindicraft before they were influenced by foreign 

 methods and ideals. Besides this, there were paint- 

 ings by some of their modern artists who adopted 

 Western methods and conventions. The contrast was 

 \'ery striking, and in some respects not very satis- 

 factory. 



Similar reflections are suggested by the present state 

 of Japanese mathematics, as shown, for example, in 

 various mathematical papers recently received from 

 the University of Tokyo. Circumstances are dif- 

 ferent because mathematical science is now cosmo- 

 politan, and no single nation can afford to neglect 

 its various developments. At the same time, hke 

 nationality in drinks, there is a kind of nationality 



NO. 273 [, VOL. 109] 



in science, art, or any other human activity, which is 

 justifiable, and even instructive, if it is not carried to 

 excess. We may notice it, for example, in the papers 

 and treatises of the leading mathematicians, such as 

 Klein and Dedekind on one hand and Poincar6, 

 Hermite, and Darboux on the other. The elegance 

 of the best French text-books is scarcely equalled, if 

 at all, by those of any other nation ; at the same 

 time, the corresponding German works are distin- 

 guished by thoroughness, method, and fulness of 

 references. The treatise on elliptic modular functions 

 by Klein and Fricke and Poincare's memoirs on 

 Fuchsian functions illustrate the point. 



It is difficult to be sure how far Japanese mathe- 

 matics is entirely original. They had various ap- 

 proximations to TT, some of which, at any rate, seem 

 to have been of their own invention. They had an 

 extraordinary gift for solving numerical equations of 

 high degrees by approximation, and one Japanese 

 writer appears to have anticipated many of Steiner's 



