428 



A' A TURE 



[March 2, 1899 



Following up his studies of the triple structure of the kathode 

 light, the author finds that the third kathode layer consists of 

 rectilinear rays, which, however, do not proceed from the kathode 

 itself, but from every point along the path of a ray of the second 

 layer. They are produced, so to speak, by a diffused reflection 

 produced at the surfaces of the gaseous particles. If K._, rays 

 impinge upon a solid substance, reflected kathode rays are pro- 

 duced. If the solid is thin enough, some of the rays penetrate 

 it, and we have Lenard rays on the other side.— Measurement 

 of very small induction coefficients, by H. Martienssen. The 

 method used depends upon the phase displacement produced by 

 the self-induction in question upon an alternating current. Co- 

 efiicients down to a few thousand cm. are thus easily measured, 

 the inferior limit hitherto attained having been lo* cm. — .\ir 

 resistances determined by means of a new rotation apparatus, by 

 O. Mannesmann. Discs arc mounted at the end of a horizontal 

 arm, and are turned about a vertical axis by means of a water- 

 power or electric motor. The air resistance encountered by 

 them is indicated by enabling the disc to slide backwards in its 

 mounting, in a direction contrary to the direction of motion. 

 In sliding back it pulls a string which passes over a pulley on 

 the axis of rotation, and supports a weight which is thus pulled 

 up. The amount of raising is indicated by an aluminium 

 pointer on a scale. Thus the amount of air resistance can be 

 read oft" at any instant. The author finds that warm air offers, 

 if anything, a greater resistance than cold air. The resistance 

 encountered by a perforated surface is smaller in proportion to 

 its remaining surface than an unperforated surface This fact 

 has a practical application to sailing practice. — A new type of 

 volumenometers, by A. Oberbeck. Two parallel glass tubes 

 ending in glass vessels are fixed side by side on a board which 

 can be tilted to any desired angle. The vessels have ground 

 edges, and can be hermetically closed by means of greased glass 

 plates. The tubes join at the other end and communicate with 

 a reservoir of mercury. On closing the vessels and lowering 

 the other end, the mercury columns descend by equal amounts 

 in the two tubes. But if the body whose volume is to be deter- 

 mined is previously inserted in one of the vessels, the mercury 

 in the corresponding tube does not descend as far as before. 

 The author shows how to calculate the volume of the body 

 from the data thus obtained. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, January 26. — "On the Nature of Electro- 

 capillary Phenomena. I. Their Relation to the Potential 

 Differences between Solutions." By S. W. J. Smith, M.A. 

 Communicated by Prof. A. \V. Rucker, Sec. R.S. 



The discrepancy between the Ilelmholtz theory of the 

 capillary electrometer and the Nernst-Planck theory of the 

 potential dift'erences between solutions is discussed in this paper. 

 A detailed examination of the relation between the phenomena 

 from which the discrepancy arises, shows that these phenomena 

 serve to corroborate the Nernst-Planck theory, and that they 

 further throw considerable light upon the nature of electro- 

 capillary phenomena. 



It is shown that if the Nernst-Planck theory be true, the 

 surface tension variation in the " descending " branches of the 

 capillary electrometer curve* is not solely due to an electrostatic 

 effect of the kind discussed by lielmhollz ; but that there is a 

 further effect, dependent upon the nature and concentration of 

 the solution employed in the electrometer. 



The extent to which the Ilelmholtz theory may be true is 

 discussed. It is concluded that this theory only suffices, in 

 general, to give the variation in the potential difference at the 

 capillary electrode. Whether the assumption is ever true, that 

 the potential fall at the capillary electrode is zero when the 

 maximum surface tension is reached, will depend upon whether 

 there is any case for which, when the potential difference be- 

 tween the solution and the capillary electrode is very small, 

 the non-electrostatic effect upon the surface tension can be 

 neglected. 



The non-electrostatic effect in the " descending " br.anch 

 would appear to be practically independent of the nature of the 

 anion, while that in the "ascending" branch is probably for the 

 nio^t part independent of the nature of the kation. Experi- 

 ments have been made with the object of determining quantita- 

 tively the manner in which the surface tension variation depends 



NO. I 53 I. VOL. 59J 



upon the chemical nature and concentration of the solution, and 

 the conditions under which such depemlence may become 

 negligible. The nature of these experiments is indicated in the 

 paper. 



February 2. — "On the Effects of Strain on the Thermo- 

 Electric Qualities of Metals." By Magnus Maclean, M.A , D.Sc. 

 Communicated by Lord Kelvin, F. R.S. 



1. Seebeck (/'c.«'. Ann , 1826) discovered the great eflPect 

 that hardness, or softness, or crystalline structure, has on the 

 thermoelectric properties of metals. Magnus made a number 

 of experiments by winding a hard-drawn w ire on a reel. Parts 

 of this wire were softened and annealed. When heat was applied 

 to the parts of the wire which were between unannealed and 

 annealed, a thermoelectric current was obtained. In this way 

 Magnus found that the current passed from soft to hard through 

 the hot junction for silver, steel, cadmium, copper, gold, and 

 platinum ; and that it passed from hard to soft through the hot 

 junction for German silver, zinc, tin, and iron. 



2. Lord Kelvin describes, in vol. ii. of his "Mathematical 

 and Physical Papers," a number of qualitative experiments to 

 determine the direction of thermo-electric currents in the same 

 metal when one part of it is left unstrained, and the other is- 



(1) Permanently affected by application and removal of longi- 



tudinal stress ; 



(2) Permanently afl'ected by application and removal of lateral 



pressure ; 



(3) Under a longitudinal stress (a) within its limits of elasticity, 



and {/i) beyond its limits of elasticity ; 



(4) Hardened by twisting ; 



(5) .-Vnnealed. 



3. He showed that for iron and copper permanent longi- 

 tudinal extension gave the .same effect .as permanent lateral 

 contraction ; and that this effect for both was opposite to that 

 experienced by ihem when under a stress which caused a tem- 

 porary strain. Thus for a copper wire under a longitudinal 

 stress the current w.as from the strained copper to the free 

 copper across the hot junction, and the magnitude of the current 

 increased with the increase of the longitudinal stress. If the 

 stress were removed and the wire left with a permanent strain, 

 the current was now from the free copper to the strained copper 

 through the hot junction. Similar results were got with iron, 

 only the direction of the current was in each case opposite to 

 the direction of the current in the corresponding case for copper. 

 The highest temperature used in these experiments was about 

 100' C. 



4. To determine the magnilude of the thermo-electric efliects 

 obtained from any one metal, strained and unstrained, was the 

 object in view in these experiments. 



The metals so far tried are : — 



(1) Copper wire from Messrs. John.son and Matthey. This 



was pure electrotype copper wire with no impurity de- 

 tected except an unweighable trace of iron. 



(2) Copper wire, ordinary commercial, from Messrs. Johnson 



and Matthey. This was analysed ' in the chemical 

 laboratory of the L'niversity, and was found to contain: — 



(3) Copper wire, used for alloying with gold and silver, from 



Messrs. Johnst)n and Matthey. This also was analysed, 

 and it contained 99 85 i>er cent, of copper. 



(4) Copper wire from Glover. Chemical analysis showed that 



it contained 9S'35 per cent of copper. 



(5) Copper wire of ( Hover's manufacture, and supposed to be 



soft, and to have a very high conducliviiy. It contained 

 990S per cent, of copper and o 22 per cent. o( lead. 



(6) Copper wire used in laboratory experiments. It contained 



9851 percent, of copper. 



(7) Lead wire, <dn>mercial. It contained 98 9 per cent, of 



lead. 



(8) Lead wire, pure.'-' It containetl 98 97 per cent, of lead. 



' All the clionii. ill ..iK.ly>e> sl.ilcd in this paper were Kiven by Mr. Ander- 

 son, of the Ciiiiiii. A 1 ..Iwr.ilory of this i;nivcr>ily. 



a These specliiK-iiv ..t commercial and pure lead wires wee ohtained from 

 Messrs. ILaird .mil lailo.k of CLasgow. Olher >peciiiiriK have been 

 ordered eKcwlRTc I'.r ., fresh determination. 



