398 



NA rURE 



'{Feb. 24, 1 88 1 



or cylinder of brass to swing in the liquid at various deptlis. 

 Tlie whole can be raised or lowered with a micrometer screw, 

 and it is tlirown into slij^ht oscillation by means of a magnet. 

 A rectangular glass vessel is used for the liquid. The author 

 finds that with distilled h ater the resistance increases suddenly 

 and to a quite consid. ruble extent whenever the upper edi;e c^f 

 the plate comes into the free surface, and he does not douM this 

 is due to increased friction in the surface layer. The increa-e 

 of resistance from the last previous position of the plate was 

 6o'9 per cent., and with four aqueous salt solutions there was also 

 an increase, varying between 75'i to 54-1 per cent. Precautions 

 adopted to prevent the presence of foreign particles on the sur- 

 face (filtration, covering with moist filter-paper, &c.) had hardly 

 any influence on the values. Long-standing of the liquid in- 

 creased the surface-resistance, and stirring then diminished it ; 

 still it was always considerable at first. With M. Plateau, Herr 

 Oberbeck found a decrease of resistance at the surface in some 

 liquids; this was comparatively small (alcohol 1 1 '9 per cent., 

 oil of turpentine 12-6, sulphide of carbun 26-3, &c.). A small 

 addition of alcohol to water lessens its surface-resistance pro- 

 perty in a marked degree, and with further addition the mixture 

 behaves like pure alcohol. 



l.N a paper on dew and fog {ZHts. fiir Meteor. Bd. xv. ]-. 

 381) Herr Dines, from observations of the former with watch- 

 glasses exposed on different substances at night, estimates the 

 annual dew formation to be about 35-5 mm. (on grass, 26 mm.) ; 

 at the best 38 mm. The average nightly dew (in 198 observa- 

 tions) was hardly o'l mm. ; in a few ca^es 0*3 mm. ; average on 

 grass o'o; mm. Morning fog along a river course arises wlien 

 the water is warmer than the air over it. The evaporation 

 goes on more quickly than the vapour can be carried away ; 

 hence the latter is condensed and spreads as fog (similarly with 

 fogs over the Gulf Stream). The evening fog on moist low-lying 

 meadows is due to the fact that the gi-ass surface cooled by radia- 

 tion cools the lowest air-layers, so causing condensation of the 

 aqueous vapour. The fine drops of dew, Herr Dines estimates, 

 are about [o'ooi mm. in diameter ; while the finest rain-drops 

 have a diameter of 0-3 to 0-33 mm. The particles of fog vary 

 in diameter from o'oi6 to 0"I27 mm. 



The colour-changes presented in the microscope by variou' 

 substances (chiefly mineral) of uneven surface, when immersed 

 successively in liquids of different refracting power, have been 

 made by Herr Maschke (Wied. Ann. No. 12) the basis of a 

 method of distinguishing substances. Such changes may be had, 

 e.g. with small glass particles, observed in water, in oil of 

 almonds, and in mixtures of the laiter with oil of cassia. The 

 dark and the bright parts of the image show diflerent series of 

 colour.'. That the effects are simply due to prismatic action of 

 the object appears from the fact that they may be got without the 

 microscope, by looking e.g. through a tube at a piece of rock- 

 crystal in water, &c. For mineral objects Herr Maschke used 

 five liquids ; amylic alcohol and glycerine, besides the three just 

 named. By various mixtures of these a series of liquids is 

 obtained, giving any desired index of refraction from 1-333 ''^ 

 I '606. (Coloration begins v\hen the refraction of the liquid is 

 near that of the object ; when the former greatly exceeds the 

 latter a certain stability of colour appears.) The method is not 

 applicable to bodies opaque in the microscope, or having too 

 strong colours of their own ; nor yet to bodies having a greater 

 index of refraction than oil of cassia. It may, too, prove 

 difficult sometimes to find a liquid sufficiently indifferent to the 

 object. Herr Maschke indicates how the refractive indices of 

 substances may be compared by his method, and (a more 

 difficult task) numerically determined. He also gives a number 

 or his own determinations. 



An interesting study, by Herr Holtz, of the electric discharge 

 in insulating liquids appears in IViedemmn's AnnaUn, No. 1 2. 

 Among other results the length of spark is found hardly at all 

 dependent on quantiiy or on retardation of the discharge. 

 Naturally it differs in different liquids, but only in one liquid 

 (sulphuric ether) did it increase with velocity of rotation of the 

 disk (this appears to be due rather to the mode of preparation 

 than to the nature of the liquid). As in air, with dissimilar 

 electrodes, the sjarh-length is conditioned by the polarity of the 

 electrodes. The thickness, sound, and luminous force of the 

 spark depend chiefly on the electric quantity and the retardation. 

 The spark is thinner than in air, but brighter (brightest in sul- 

 phide of carbon, least bright in olive-oil and ether). It is more 

 crooked than in air. Throughout its length it shows innumer- 



able very small dark spaces. With large striking distance it 

 appears within a largely-branching brush. (The appearances of 

 the brush discharge, get best in petroleum, are also described.) 



Fro.m data obtained in various parts of Germany, Austria, 

 and Switzerland (IVied. Ann. No. 12), Herr Holtz finds a well- 

 marked increase in risk from lightning in these parts since 1854, 

 while no such increase appears in the number of thunderstorms. 

 Hence he infers the causes to be .telluric, and he suggests as pro- 

 bable causes the clearing of forests and increase of railways 

 (attracting storms more to towns and villages) ; further, the 

 increased use of metal in buildings. 



Pkof. Bo.mbini hss lately communicated to the Bologna 

 Academy an interesting paper on spherohedry in crystallisation 

 (Riv. Set. Imi. No. 21), by which he means any known manner 

 of production of a fibroUs-radiate structure. From a survey of 

 facts he concludes that the great phenomenon of crystallisation 

 comprises two different orders of attractive energy. In the first 

 there is simple centralised attraction, with concurrence of the 

 elements attracted to a common centre. In the second there is 

 attraction with directive polarity according to certain axes of 

 symmetry, and concurrence of the attracted elements towards 

 nodal points in a certain reticular .system. Between these two 

 kinds of crystallogenic action there are many gradations, or 

 rather synthese--, superpositions. Further, the correlations 

 between the sphericity characteristic of the liquid state; the 

 spherohedry of globosity w ith radiated structure; the isometry 

 of radiate pseudocubical groups ; leading from the amorphous 

 state of liquids to the absolutely reticular state of the true crys- 

 tals (isotropic, orthoprismatic, and clinohedric) confirm the 

 cubicity of the first system, and at the same time point to some 

 further significant terms in the progressive series of the physical 

 states of inorganic matter. Prof. Bombini indicates three con- 

 ditions : I. Spherohedric crystallisation; II. Polyhedric crys- 

 tallisation; and III. Pseuducubic, &c., crystallisation. The 

 third may be considered intermediate between the first and the 

 second ; the first appearing as a term of transition between the 

 sphericity of the liquid state and the polyhedry of physical 

 solidity. 



GEOGRAPHICAL NOTES 

 The February Proctedin^s of the Geographical Society opens 

 with Capt. Huldith's paper on the " Geographical Results of 

 the Afghan Expedition " ; but of more importance from a geo- 

 graphical point of view are Mr. Wilfred Powell's "Observations 

 on New Britain and Neighbouring Islands." The latter is 

 accompanied by a sketch-survey of the north-ea-t portion of 

 New Britain by the author, whxh of itself is of considerable 

 value. A correspondence between Admiral Kyder, Naval Com- 

 mander in-Chief at Portsmouth, and the Council of the Society 

 follows, by which w e learn that the latter, in declining his offer 

 to establish certain medals, are of opinion that "the plan of 

 granting medals to officers and seamen for independent surveys 

 is impracticable," and further that they do not consider it their 

 business to take any action in regard to an international congress 

 of hydrographers. 



Under the title of " Union Geographique du Nord de la 

 France," a geographical association «as formed some time ago, 

 with its head-quarters at Douai, and branches at Amiens, Arras, 

 Boulogne, Cambrai, Charleville, Dunkerque, Laon, Lille, St. 

 Omer, St. Quentin, and Valencienne--. In the first part of the 

 Bulletin of the Union, which has been sent to u-, the list of 

 members covers about fifty pages. The object of the associa- 

 tion is by every means to pr. mote the development and spread 

 of geographical knowledge, investigating specially questio s re- 

 lating to the industry, -commeice, and agriculture of the region of 

 the Nord. The Bulletin, a volume of some size, contains papers 

 on the Exploration of the Sahara, Nordenksjold's last voyage, 

 a Project for Exiiloring the Welle, the Proposed Canal betv/een 

 the Atlantic and the Meditenai-.ean, and the Maritime and Com- 

 mercial Statistics of Dunkerque. In the Comptes rendus of the 

 meetings of the various societies are abstracts of papers on a 

 great variety of sulijects, and there are besides a geographical 

 chronicle and a pretty full bibliography. We have no doubt 

 the Association will do much good in the North of France. 



Prof. Ujfalvv has left St. Petersburg on his return from 

 Central Asia. The journey he m.ade during last summer was 

 not so successful as his preceding ^tr.avels, because of a serious 



