June 



■0 



NATURE 



179 



issued in parts, and when complete, will form two volumes, 

 illustrated with engraving-;. 



Herr Scholer, who was sent out by the German African 

 Society, has returned to Zanzibar after founding a station at 

 Kikoraa. 



The Italian traveller, Piaggia, returned to Khartum on April 

 30. It is believed there that he will be appointed governor of 

 the Fashoda district, and that the Austrian, Maruo, will become 

 governor of the province of the Blue Nile. 



The Scientific Commission, recently despatched from Paris, 

 has arrived at Zanzibar on its way to examine M. Paiva's vast 

 concession in the Zambesi region, which it is proposed to develop 

 by means of a cojipany. The Commis;iou is to investigate the 

 resources of the territory, chiefly with regard to the mineral 

 wealth supposed to exist there. 



PHYSICAL NOTES 



A FEW months ago the phenomenon of the "passive state" 

 of iron was examined by 5l. L. Varenne, who attributed it to 

 the presence of a film of nitrous acid gas upon the surface of the 

 metal. The question has been recently reinvestigated by M, E. 

 Bibart, who finds reason to doubt M. Varenne's conclusions. M. 

 Bibart states that any oxidising agent aids, and any deoxidising 

 agent hinders, the production of pasavity. 



In a long memoir presented to the Academic des Sciences by 

 Edmond and Henri Becquerel some very valuable data are given 

 respecting the fluctuations of underground temperatures during 

 1880 beneath difierent surfaces. Their observations extended to 

 a depth of 36 metres. The fluctuations were of less extent 

 beneath herbage than below a bare soil, the maxima and^minima 

 being more retarded and of less amplitude in the former case. 

 Another interesting point is the protecting effect of a bed of 

 snow. Though the temperature of the air fell to - 15°, and 

 continued below 0° for long periods, that of the surface of the 

 soil was rarely below - 1°, never below - l°'5. 



According to Nies and Winkelmann, who have lately studied 

 the expansion exhibited by bismuth, cast-iron, and other metals 

 . during their solidification, the specific gravity of bismuth is 

 between 1-031 and I "0497 times as great in the liquid as in the 

 solid state ; a sample whose (solid) density was io'2 assumed a 

 density of 1077 when melted. The ratio of the density in liquid 

 state to that in solid state was greater than unity also for the 

 metals tin and zinc, the ratio for tin being I '0070, and for zinc 

 I -002. Our readers will doubtless recall the recent experiments 

 of Mr. Wrightson and Prof. Chandler Roberts in the same 

 direction. 



Herr Stucker concludes from experimental inquiry ( IVied. 

 Ann. No. 5), that the gases chlorine, bromine, and iodine, in 

 regard to thermal behaviour, form a group by themselves among 

 biatomic gases. The ratio of the kinetic energy of the pro 

 gressive motion of the molecules to the total energy is different 

 for them from that for the others. In their molecules the 

 atoms seem to have a different reciprocal action. From the 

 behaviour of biatomic gases it is inferred that neither Boltz- 

 mann's nor Maxwell's supposition as to the nature of the mobility 

 of atoms in the gaseous molecule has a general validity. 



With regard to the subject of hot ice, Herr Wiill ler describes 

 fresh experiments (/f'm/. Ann. No. 5), and he finds that so 

 long as the thermometer-bulb is wholly surrounded with dry ice 

 its temperature does not reach 0°. If the thermometer rises 

 higher, either the bulb is no longer quite co\ered with ice, or 

 it is surrounded with water, along with a thicker ice-layer. The 

 aiithor's method was to have the thermometer-bulb first coated 

 with ice in a separate vessel ; then introduced into the heating- 

 tube and fixed in a caoutchouc stopper ; this tube is connected 

 through a tube and spherical vessel with the air-pump, and with 

 the sphere is surrounded with a cold mixture while the vacauni is 

 produced. 



The subject of double refriction of light in moving frictional 

 liquids has been taken up anew by Herr Kundt ( Wied. Ann. No. 5), 

 using a method which Maxwell did not succeed with, viz., rota- 

 tion of a cylinder within another cylinder, and sending a beam 

 of polarised light in axial direction through liquid in the annular 

 space. Herr Kundt got positive results in this way with various 

 liquids. I. The amount of internal friction of liquids is not a 

 certain measurement of the occurrence of double refraction in 



motion ; liquids with small friction giving considerable refrac- 

 tion, and vice versa. 2. The liquids which, with small internal 

 friction, prove doubly refractive, belong to the so-called colloids 

 (gelatine, gum, collodion) or the oils. Solutions of crystalloids 

 did not give the phenomenon by the method described. 3. The 

 double refraction did not markedly affect the rotation of the 

 plane of polarisation in the circularly polarising liquids (but the 

 strongest refraction, it is to be noted, produced a difference of 

 only about half a wave in penetrating a pretty long column of 

 liquid). 4. In collodion-solutions the axes of the double refrac- 

 tion do not lie in the azimuths required by theory. The anomaly 

 was not accounted for. Herr Kundt further oflers some general 

 remarks on the relations between the elastic properties of liquids, 

 their coefficients of friction, and the double refraction developed 

 in them. 



It has been hitherto supposed that light directly reflected from 

 a diffraction-grating has the same state of polarisation as light 

 passing 'through the same plate unruled, or reflected from its 

 smooth surface. Herr Frohlich now finds, with a very finely- 

 ruled grating, that it is not so. The proof and numerical amount 

 of the difference are indicated in IVied. Ann. No. 5. 



In the cold of last winter M. Damien (yourn. de Phys., May 

 investigated the indices of refraction of water under 0° {i.e. in 

 sarfusion) down to - 8°. He measured the indices corresponding 

 to the three hydrogen lines by the prism method. Starting with 

 a temperature of -t- 20°, he first confirmed M. Jamin's observa- 

 tion that the passage through the maximum of density does not 

 at all disturb the course of the indices, and he further found that 

 the indices continue to increase below zero, though the density 

 diminishes. The variations of the indices are very small. M. 

 Damien hopes, next winter, to apply the interferential method. 

 (The use of freezing mixtures does not present such favourable 

 conditions as the very slow cooling of the atmosphere.) 



Recent researches by Herren Sohncke and Wangerin on 

 Newton's rings (IVied. Ann. Nos. 3 and 4) appear to require a 

 considerable change of ideas as to this phenomenon, and more 

 especially as to the place where interference occurs. The 

 starting-point was an experiment in which the rings produced 

 by a beam of parallel sodium light falling at an angle on a 

 horizontal plate above a plane convex lens were examined with 

 a microscope inclined at the same angle, and capable of being 

 moved horizontally as well as in the direction of its axis. The 

 microscope was first so placed that one part of a dark ring was 

 as sharply defined as possible ; the instrument being then moved 

 along to another ring, or another part of the same ring, it was 

 foand necessary to move it axially, higher or lower, to get the 

 maximum definition for that part ; indicating that the rings do 

 not lie in a horizontal plane, but in some other position. The 

 amounts of axial displacement for different parts of the ring- 

 system were carefully noted. For details of the results we must 

 refer to the original, merely noting, inler alia, that the places of 

 interference in the plane of incidence going through the centre 

 of the rings seem to lie in a straight line rising towards the side 

 whence the light comes. In a central plane at right angles to 

 that of incidence, all the places are at the same depth. Herr 

 Sohncke undertook the experimental part in this investigation, 

 while Ilerr Wangerin has worked out the theory of the phe- 

 nomena. 



According to experiments by Herr Kundt (Wied. Ann. 

 No. 4), the common surface-tension between liquid and gas 

 decreases considerably with increasing pressure of gas in the 

 case of alcohol, ether, alcoholic solution of calcium-chloride, 

 sulphide of carbon, chloroform, and water. The decrease is 

 greater at low pressures than at high. For a given liquid it 

 varies with the nature of the gas compressed. With alcohol, 

 ether, and alcoholic chloride of calcium solution, air causes a 

 greater decrease of the capillary constant than hydrogen. The 

 decrease is so great with some liquids (e.g. ether in air) that 

 probably, with pressures reached without much diflicnlty, the 

 surface-tension is nil, the liquid passing at ordinary temperature 

 into the Cagniard de la Tour state. (The author's experiments 

 were concluded before he knew of Cailletet's experiment, in which 

 a mixture of five vols, of CO.j and one vol. of air is compressedat 

 a low temperature till the meniscus of CO; disappears, and the 

 Cagniard de la Tour state is reached.) 



The ratio of intensity of the two sodium lines has been esti- 

 mated by Herr Dietrich (Wied. Ann. tio. ^) using apparatus 

 of great dispersion with a Vierordt double slit giving one spec- 

 trum above another, and allowing of displacement, so that one 



