304 



NA TURE 



[January 30, 1908 



gave the results of an experimental investigation by means 

 of india-rubber models. The following are some of the 

 conclusions given : — (i) Tensile stresses may exist at the 

 up-stream toe of a dam, notwithstanding the fact that the 

 line of resistance lies well within the middle third. The 

 tension may be reduced by (a) making the up-stream face 

 vertical, or by otherwise increasing the weight of the 

 dam toward that face ; this would have the effect of in- 

 creasing the stresses in the dam when the reservoir is 

 empty ; (b) by a general increase in the dimensions of Ihe 

 dam ; (c) by placing an earth embankment against the 

 down-stream face. (2) The direct stresses at the down- 

 stream toe are compressive in every direction, but reduce 

 to zero /n the direction norma! to the face. (3) The 

 maximum compressive stresses in a dam above its founda- 

 tions are in a direction approximately parallel with the 

 down-stream face, and generally some distance therefrom. 

 In magnitude they are slightly greater than 



Pt 



cos- 0' 



where Ft is the maximum normal pressure on a horizontal 

 plane as determined by the trapezium law, and ^ is the 

 angle between the resultant and the vertical. (4) The 

 shearing stresses are considerable at or near the up-stream 

 toe. They are a maximum a short distance from the down- 

 stream face, in a plane approximately at 45° to the face. 

 The maximum shearing stresses are in magnitude equal to 



Pr 

 2 COS- <^ 



(5) The stresses in the foundations are of less consequence 

 than in the dam above the base, because of the lateral 

 support and the more extended distribution. (6) The 

 stresses are considerable at the toes of a dam if they form 

 sharp angles with the foundations. These stresses may 

 be reduced by replacing the angles with curves of large 

 radii. The curve at the up-stream toe may take the form 

 of a rounded quoin, cut in large stones, so as to avoid 

 joints, in the masonry, normal to the direction of the 

 greatest tensile stress. 



In the third paper Mr. E. P. Hill described a method 

 of determining stresses based on the assumption that the 

 vertical pressure on the base varies uniformly from one 

 side to the other. 



AVSTRIAN SCIENCE. 



'T'HE monthly parts of the Sitzungsberichie of the Vienna 

 Academy of Sciences which appeared last year 

 show that there is no falling off in the research work 

 carried out at the Austrian universities in the fields of 

 mathematics and natural philosophy. Prof. Lecher, of 

 Prague, has verified Ohm's law by showing that there is 

 no difference in the resistance of a silver or platinum wire 

 when a small or a large electric current passes through 

 it, provided its temperature is the same in both cases. 

 Assuming that the current is carried by one type of free 

 electron, he deduces a velocity of propagation of electricity 

 in ordinary cases of the order of a few centimetres per 

 second. 



Prof. F. Exner and Dr. E. Haschek have been engaged 

 in a search for the cause of the slight variability of wave- 

 length of many of the spectral lines with the method of 

 ■excitation. They are disposed to attribute it to the lines 

 for which it has been observed being complex, with 

 satellites of variable intensity or number which appear 

 to be present more frequently on the red than on the blue 

 side of the line. In an instrument of only moderate 

 resolving power, the apparent effect of any cause tending 

 to increase the intensify of such satellites with respect to 

 the original line will be a displacement of the line towards 

 the red end of the spectrum. 



Dr. N. .Stiicker has investigated the sensitiveness of a 

 Croat number of persons to small differences of pitch in 

 different parts of the musical scale. He finds that in 

 general the region of maximum sensitiveness is in the 

 ■octaves c' and c^, where about i/20th of a tone can be 

 detected. A few musical people .'were able to detect a 

 difference of i/2ooth of a tone in' this region. The higher 



NO. 1996, VOL. yy] 



limits of audibility varied from about 40,000 in general to 

 more than 60,000 in the case of musicians. 



The meteorological side of the activity of the academv 

 is well represented by Dr. F. M. Exner's outlines of a 

 theory of variation of atmospheric pressure. The prin- 

 cipal result of this investigation is that the pressure vari- 

 ations may be represented by the motion of a relatively 

 permanent system of isobars over the surface of the earth 

 from west to east with a velocity varying slightly with 

 the season. 



An important series of papers by Prof. Rudolph 

 Wegscheider and Dr. Heinrich Walter, published in the 

 Sitziiiigsberichtc (vol. cxvi., pp. 443, 455, and 533), throws 

 a great deal of light on the phenomena occurring when 

 soda is causticised by means of lime. On the one hand, 

 the conditions of equilibrium for the reversible change 

 Ca(OH),-l-Na,CO,rrCaC03-l-2NaOH have been asccr 

 taincd at different temperatures ; that the change is a 

 reversible one is shown by the fact that the same con- 

 dition of equilibrium is established at a definite tempera- 

 ture whether the lime acts on sodium carbonate or caustic 

 soda on calcium carbonate. The change in the direction 

 from left to right seems to be more complete at So° than 

 at io6°-iio°, and to occur more readily in dilute than in 

 concentrated solutions ; the way in which it is influenced 

 by concentration is considered at some length from the 

 standpoint of the theory of mass action. The loss of 

 sodium carbonate which may occur in the more concen- 

 trated solutions owing to the formation of the mixed 

 carbonate, CaCOj.NaXOj, is also fully dealt with, the 

 conditions under which gaylussite, CaNa.(C03),,5H„0, 

 and pirsonnite, CaNa,(C0,),,2H,0, are capable of exist- 

 ence in contact with solutions of sodium carbonate and 

 caustic soda being defined for different temperatures. It 

 is noteworthy that the decomposition of both of the double 

 salts by water is retarded owing to the formation of a 

 protective sheath of insoluble calcium carbonate on the 

 surface of the particles, so that if the mixed salt is once 

 precipitated owing to the concentration becoming too 

 great, loss of sodium carbonate may occur even though 

 the insoluble material be well washed. The whole investi- 

 gation has a special interest as illustrating the applicability 

 of recently developed views in pure chemistry to the 

 elucidation of technical problems. 



During several years past the study of the general laws 

 of esterification, especially of the influence exercised by 

 structural peculiarities on the phenomena, has formed a 

 special feature of the research work carried out under the 

 direction of Prof. Wegscheider in the first chemical labor- 

 atory of Vienna University. The results obtained have, 

 in particular, thrown considerable light on the nature of 

 the so-called " steric hindrance." In continuation of these 

 researches a series of papers by .'\nton Kaiian appears in 

 the Sitzungsberichte of the academy dealing with the 

 esterification of the dinitrobenzoic acids, of mono- and 

 di-hydroxybenzoic acids, and of pyridinemonocarboxylic 

 acids by alcoholic hydrogen chloride. Prof. Wegscheider 

 and E. Frankel discuss in considerable detail the reasons 

 for abnormalities which sometimes are found to charac- 

 terise the action of alkyl haloids on metallic salts of 

 organic acids. The peculiar influence exercised by the 

 presence of a small proportion of water on the rate of 

 formation of ethyl chloride from alcohol and hydrogen 

 chloride is the subject of a paper by A. Kaiian, in which 

 it is shown that the velocity constants of the action are 

 proportional to the concentration of the hydrogen chloride 

 only in absolute alcohol. In alcohol containing water, 

 even in 99-9 per cent, alcohol, an increase in the concentra 

 tion of the hydrogen chloride is found to be accompanied 

 bv a considerably greater increase in the velocity constant. 

 To vol. cxvi. of the Sit::ungsbcrichtc (mathematisch- 

 natiirwisseiischaftliche Klasse) of the academy Mr. F. 

 Siebenrock contributes a monographic revision of the 

 American tortoises of the family Cinosternidae, in which 

 several changes in the generally accepted classification are 

 proposed. In the British Museum Catalogue of Chelonians 

 the family is taken to include only the single genus Cino- 

 sternum, while Claudius and Staurotypus are included 

 with Derrnatemys in the family Dermatemydidre. This 

 the author regards as an unnatural arrangement, and he 

 proposes to transfer Claudius and Staurotypus to the Cino- 



