May 19, 1881] 



NA TURE 



67 



of an important fact in connection with this subject, namely, that 

 when the arc begins to emit the well-known hissing sound there 

 is an abrupt change in the opposing electromotive force, which is 

 greater while the arc is silent than when it is hissing. 



MM. Naccari and Pagliani have lately determined the 

 vapour tensions of a number of liquids in the laboratory of the 

 University of Turin. Their method consisted of a modification 

 of that of Regnault, reduction of pressure being effected by an 

 aspirating pump. The tensions of toluene, propylic and iso- 

 butylic alcohol, and of several of the ethers of the fatty acids 

 were determined at different temperatures with great exactitude 

 and their empirical formula: calculated. 



From a study of the electromotive force of inconstant couples 

 MM. Naccari and Guglielmo conclude that in couples containing 

 one fluid the electromotive force is ioflueuced by the nature of 

 that pole to which the hydrogen goes, and that the change in 

 the strength of the current varies always in the oppo.-ite sense to 

 that of the electromotive force, the sense depending upon the 

 manner in which the liberated oxygen enters into secondary 

 chemical actions. 



At the Ob;ervatory of Campidoglio, Prof. Respighi has been 

 lately conducting a series of experiments for the determination 

 of gravity. The data are not as yet fully reduced, but the 

 author has described his method {Atli dclla R. Ace. dei Lined, vol. 

 V. fasc. 5), which consists in the use of a pendulm with a lead 

 ball about gi kg. in weight, and a steel v ire o"6 mm. in dia- 

 meter ; a sharp iron point at the extremity, dips in mercury 

 each oscillation, so as to give passage to the current of a chrono- 

 graph. Five different lengths of pendulum were used, between 

 7*90 m. and 5'i6 ui. ; and with all these lengths tlie pendulum, 

 on account of its weight, the fineness of the wire, and the con- 

 venient mode of suspension, proved independent of the rotatory 

 motion of the earth, presenting Foucault's well-known pheno- 

 menon (an essential conditicn, in the author's opinion, but not 

 verified in Borda's or Bessel's apparatus). The number and 

 duration of the oscillations were registered by the chronograph 

 with greater exactness than is attainable by the method of 

 coincidences. 



An arrangement for rendering Volta's pile constant and depo- 

 larised is described by Count Mocenigo in a recent number of 

 the Rivista Scicntijico-Indiistriale. Twelve couples with their 

 elements are fixed on a horizontal axis ; a trough of acidulated 

 water having twelve compartments is brought up by a lever 

 motion, so as to cover a good third of the surface of the pile, 

 and a rotatory movement is communicated to the axis. 



The velocity of sound in chlorine has been determined lately 

 by Prof. Tito Martini (Riv. Sci. Itid., No. 6), no physicist 

 having previously, to l-is knowledge, done so. His method 

 was suggested by an experiment of Tyndall. A glass lube 

 40 ctm. long and 2 ctm. internal diameter, and fixed in vertical 

 position, was connected below, by means of a gutta-percha tube, 

 to another glass tube holding sulphuric acid, and capable of 

 being raised or lowered so as to vary the level of the liquid 

 entering the fixed tube, in order to obtain the column of gas 

 which would : trengthen a certain tone. The fixed tube was 

 graduated in centimetrts and millimetres. Having first verified 

 the accuracy of the method by experiments with carbonic acid 

 and protoxide of nitrogen, the author proceeded to chlorine, and 

 obtained 2c6'4 m. as mean value of the velocity of sound in it 

 for zero temperature. 



The mode of decomposition of water by discharge of Leyden 

 jars through platinum electrodes has been studied by Dr. 

 Streinlz (Vienna Acad. Aiiz.). Riess attributed this pheno- 

 mena to heating of the electrodes. Using a quadrant-electro- 

 meter, &c., Dr. Streintz found that with very small electrodes 

 giving passage to a series of discharge-currents in one direction, 

 then left to themselves, a remarkable reversal of electromotive 

 force occurred, but only when the discharges did not exceed a 

 certain number. The author was led to examine the change of 

 electromotive force by short galvanic currents, which also pro. 

 duce, in a few minutes, a reversal in the electric behaviour of 

 the electrode covered with H; ; and he explains this by saying 

 that platinum containing no free, but only occluded, hydrogen is 

 electromotively negative to pure platinum. The further observa- 

 tion that a fully-polarised cell, one of whose electrodes was 

 covered by a very brief galvanic current with H.^ the other with 

 Oj, did not show a reversal of the difference of potential, led 

 to the conclusion that the decomposition through battery dis- 



charges is to be regarded as the product of a galvanic polarisation 

 and a connected (thermal ?) development of oxyhydrogen gas on 

 the two electrodes. 



In a recent note to the Vienna Academy Prof. Reitlinger and 

 Dr. Wachter di-tinguish three varieties of Lichtenberg figures : 

 (i) the positive radiating figure {StraJihnfigur) ; (2) the positive 

 disk-figure ; (3) the negative disk-figure. The (2) was lately 

 added by Herr Holtz. The conditions of production in each 

 case are investigated. The positive radiating figure is produced 

 (according to the authors) by dust particles detached and carried 

 off from the electrode ; the negative disk-figure, on the other 

 hand, by g.is-discharges. In the former case the particles, while 

 they communicate their positive electricity to the resin, describe 

 radial paths rendered visible and yellow by the dusting process. 

 The rea'On why one never gets a negative (red) radiating 

 figure, or even branch, is that the electro-negative discharge 

 from a metal or other conductor in air is neither capableof 

 effecting an electric disaggregation of the electrode, nor a 

 carrying away of dust-particles. 



To obtain an enlargement (on a screen) variable at will, at 

 any distance, M. Crova (fourn. de Phys., April) places between 

 the object and the screen (which are fixed) a projection-apparatus 

 formed of two lenses, one convergent (plane-convex), the other 

 divergent (plane-concave), of the same focal distance, and 

 capable of being moved apart by means of a rack and pinion 

 arrangement. 



GEOGRAPHICAL NOTES 



Mr. James Glaisher writes from the office of the Palestine 

 Exploration Fund, announcing the discovery of a " Ilittite " 

 City. — "A great battle," he states, " figured in Sir G. Wilkin- 

 son's 'Ancient Egyptians' was fought between Rameses II. and 

 the Hittites near their sacred city of Kadash, which is shown as 

 a city with a double moat, crossed by bridges beside a broad 

 stream running into a lake. The lake has been generally 

 identified with the Baheiret Homs, through which the Orontes 

 passes south of Homs, but the site of the city, as important In 

 Hittite records as the northern capital of Carchemish, remained 

 to be discovered. We now leani from a despatch received 

 from Lieut. Conder, the olVicer in charge of our new expedition, 

 that he has identified the lost site w ith the ruins known as the 

 Tell Neby Mendeh. They lie on the left bank of the Orontes, 

 four English miles south of the lake. The modern name be- 

 longs to a sacred shrine on the highest part of the hill on which 

 the ruins lie, and the name of Kade.-h still survives, so that here 

 is another instance of the vitality of the old names which linger 

 in the minds of the people long after they have forgotten the 

 Roman, Greek, or Crusaders' names. Not only the name is 

 preserved, but the ancient moat of the city itself. Lieut. 

 Conder writes :— ' Looking down from the summit of the Tell 

 we appeared to see the very double moat of the Egyptian 

 picture, for while the stream of the Orontes is dammed up so as 

 to form a su\ill lake fifty yards across on the south-east of the 

 site, a fresh brook flows in the west and north to join the river, 

 and an outer line of moat is formed by earthen banks, which 

 flank a sort of aqueduct parallel with the main stream.' " 



The French Government is taking advantage of the occupa- 

 tion of a part of Tunis to extend their ordnance survey_ to 

 regions hithnto untrodden by ordinary travellers. Col. Perrier, 

 the member of the Institute who is at the head of the French 

 Survey, has been ordered for this service. 



The death is announced of Gessi Pasha, the friend and coad- 

 jutor of Col. Gordon in the Sudan. He died on the evening of 

 April 30, in the French hospital at Suez, after protracted suffer- 

 ings caused by the terrible privations he endured in the months 

 of November and December last, when he was shut in by an 

 impassable barrier of weed in the Bahr- Gazelle River, Upper 

 Egypt, as already recorded. Capt. Gessi conducted some valu- 

 able exploring work on the Nile under Col. Gordon, and in 1876 

 succeeded in circumnavigating Albert Nyanza, adding greatly to 

 our knowledge of that lake. 



In the Rei'ue Scientifique of May 14 M. G. Rolland has a 

 long article on the Sand Dunes of the Sahara, in which he 

 adduces data to show that these dunes shift but very little, that 

 although they move towards the south-east, it is very slowly, 

 and that little difference is made upon them in the course of a 

 generation. 



