no 



NA TURE 



[June i, 1893 



a slit at 45 degrees to the horizon, and pass through the diffu- 

 sion vessel on to a screen. The dividing surface is indicated by 

 a decided upward or downward bend of the line on the screen, 

 which becomes gradually less pronounced and more evenly dis- 

 tributed as diffusion equalises the refractive indices. The 

 amount of vertical displacement at each point of the curve 

 measures the difference of concentration in the region traversed 

 by the ray. The constant of diffusion can be calculated from 

 the rate of change of the diffusion curve, and the displacement 

 of the point of maximum bending indicates the lesser diffusivity 

 of the liquid towards which it takes place. Ilerr Wiener has 

 also successfully applied the method to the determination of the 

 thermal conductivity of water by photographing the diffusion 

 curve in various stages. 



The question as to whether there is a true hysteresis in the 

 case of dielectrics has received considerable attention lately, 

 and Arno, Hess, and Janet have published the results of exten- 

 sive researches on this subject. A note by M. Charles Borel 

 in the current number of the Coviptes Kendus has some bearing 

 on this point. He suspends a disc of paraffined paper by its 

 centre in front of a plate which is charged, by means of a 

 rotating commutator, alternately positively and negatively. 

 The duration of the charge was 0'006 second, and between 

 charges of opposite sign it was put to earth for an equal intervals 

 When a glass rod is placed on one side of the disc, so that the 

 plane of the disc and the axis of the rod are parallel to the lines 

 of force of the field, and the end of the rod nearest the charged 

 plate is slightly inclined towards the disc, the latter is rotated. 

 This rotation can be explained by the mutual action of the 

 residual charges in the disc and glass rod when the charged 

 plate is earthed. Different specimens of glass produced very 

 different re.sults on the suspended disc, some having no effect 

 whatever. The replacement of the disc of paraffined paper by 

 one of mica had little effect, while discs of pure paraffin or 

 ebonite showed only a feeble effect. It was found that rods 

 formed of conductors or of go id insulators, such as ebonite and 

 shellac, produced a feeble rotation in the opposite direction to 

 that produced by most dielectrics. If the rotation is really due 

 to the residual electrification of the disc or rod this rotation in 

 the inverse direction may be expected whenever the rod has no 

 residua! electrification. The effects of crystals held in different 

 directions was tried, and it was found that, in general, the 

 deflection varied with the direction of the crystal, which was 

 normal to the charging plate. 



Wiedemann's Annalen for May contains a paper by Herr 

 J. von Geitler on the reflexion of electrical waves in wires. 

 The waves were generated by means of the arrangement 

 used by Blondlot, the secondary circuit being connected 

 to two parallel wires 280 metres long. The variation of 

 potential along these wires was measured by means of a 

 differential electrometer, consisting of a double aluminium 

 needle suspended by a quartz fibre before four metallic plates. 

 These plates were connected, two and two, to the parts of the 

 wire whose difference of potential had to be measured, in 

 such a way that the attraction between the pairs of plates 

 tended to turn the needle in opposite directions. The experi- 

 ments show that if a series of electrical waves travel along two 

 equal and uniform parallel wires there is a regular loss of phase 

 and partial refexion wherever the parallelism of the wires is 

 destroyed, or wherever there is a change in the diameter of the 

 wire. Tae same effect is produced by joining the plates of a 

 condenser to the two wires at any point. The curves showing 

 the connection between the electrometer throw and the length 

 of a branch circuit attached to the main wires are of a very 

 curious form, and owing to the loss of ha|f a wave length at the 

 reflexion at the end of the branch circuit in one case, the curve 

 NO. I 231, VOL. 48] 



obtained when the ends were separate was the exact inverse of 

 that obtained when the ends were joined together. 



Mr. W. Roe contributes to the Agricultural Journal, of 

 Cape Colony (April 6) an interesting paper on some of the dis- 

 advantages that may result from irrigation. Most water used 

 for irrigation contains variable quantities of soluble salts, more 

 especially soda salts, chlorides, and sulphates, not t.iken up 

 largely by plants. Every application of water, therefore, adds- 

 to the saline ingredients of the soil — a very different effect from 

 that of excess of rain water, which so far as there is open sub- 

 soil for it to drain away would be likely to take out rather than 

 add to the soluble salines in the soil. This mischief, accumu- 

 lation of salts in the soil, is aggravated in a dryair land where 

 evaporation is great. The air, acting like a sponge on a surface, 

 takes up the water, leaving the accumulated salts in the surface 

 soil. But this surface soil is as the sponge to the layer beneath. 

 Constantly after each water-leading the water is drawn to the 

 surface, and evaporated, and its measure of salts left behind. 

 Obviously the harm done by this accumulated salt will depend 

 on the nature and quantity of the salines in the water used, as 

 also upon the quantity of water applied. A good quality of 

 river water may vary in having five to twelve grains to the gal- 

 lon of soluble salts ; more than this becomes risky, unless 'he 

 sub-soil is very porous. 



The Rugby School Natural History Society has issued its- 

 report for the year 1892. The report, as the editor explains, 

 differs from those of previous years in that the papers included 

 in it deal solely with the natural history of the neighbourhood. 

 They are all, with one exception, reprinted from the Rev. W. 

 O. Wait's " Rugby, Past and Present," and as in the main they 

 are written by old members of the Society, they may be re- 

 garded as presenting a kind of summary of the Society's work 

 from its foundation to the present day. 



A paper on the Siyin Chins, by Major F. M. Rundall, is 

 included in the third volume of the " Supplementary Papers" 

 of the Royal Geographical Society, and has also been printed 

 separately. The author knows the Chin Hills well, and gives 

 a very interesting account both of them and of the tribes by 

 which they are inh.abiled. The paper is accompanied by a map. 

 The new instalment of the proceedings of the Geologists* 

 Association includes the presidential address of Prof. J. F. 

 Blake, delivered on February 3. It deals with the basis of the 

 classification of Ammonites. 



An essay on the laws of heredity, read originally by S. S. 

 Buckman before the Cotteswold Field Club, has been translated 

 into German, and issued as one of the series of " Darwinislische 

 Schriften," published by Ernst Giinther, of Leipzig. The 

 Geiman title of Mr. Buckman's work is " Vererbungsgesetze 

 undihre Anwtndung auf den Menschen." 



Messrs. Croshv, Lockwoou and Son will issue in a few 

 days an English edition of the "Handbook of the Steam 

 Engine," by Herm. Haeder. The editor and translator of the 

 English edition is Mr. H. H. P. Powles. 



"A Contribution to the Chemistry and Physiology of 

 Foliage Leaves," by H. T. Brown, F.R.S., and Dr. G. H. 

 Morris, has been reprinted, by Messrs. Harrison and Sons, 

 from the "Journal of the Chemical Society," May, 1893. 



The Entomological Society of London has issued a catalogue 

 of its library. The work has been edited by G. C. Champion, 

 hon. librarian, assisted by R. McLachlan, F. R.S., and D. 

 Sharp, F. R. S. Great additions to the collection have been 

 made since the last printed catalogue was published in 1861 ; but 

 there are still certain deficiencies, and Mr. Champion expresses^ 

 a hope that some of these may be speedily supplied by Fellows, 

 and that the publication of a separate Appendix may thus at no- 

 distant date be rendered necessary. 



