July I, 1880] 



NATURE 



Z07 



Some experiments have lately been made by the Rev. Dr. 

 Haughton and Prof. Emerson Reynolds to evaluate the co- 

 efficient of friction (i.e. the "drag ") of air upon air and of water 

 upon water. In these experiments a spherical ball of unpolished 

 granite of 22 kilogrammes weight and 25 centimetres in diameter 

 was suspended freely by a pianoforte wire and was set rotating 

 in the air or in water ; the period of the vibrations and the 

 decrement of their amplitudes being obferved by means of 

 indices attached to the brass collar by which the ball was sus- 

 pended. A discussion of the equations of motion led to a simple 

 worlung equation for reduction of results. The mean coefficient 



of friction found fjr air upon air was / = 



60527 



though this 



value apparently differed slightly according to barometric and 

 thermometric conditions. For the " drag " of water upon water 



the value found was / = ~. These experiments involved fric- 



307 

 tion at low velocities only, for which it could be asiumed that 

 the friction was proportional to the velocity. The authors of 

 this research point out that these results tend to negative the 

 theory of Dr. Carpenter that the phenomena of ocean circulation 

 are due to the greater height of the water at the equator as com- 

 pared with that at the poles. 



From a series of experiments with tones produced by a limited 

 number of impulses, Herr Kohlrausch finds (IVicd.Anti., No. 5) 

 that a tone of only two vibrations of a certain frequency can be dis- 

 tinguished as d iffering in pitch from a continuous tone, when it forms 

 with it an interval of |4. Also, in agreement with the researche; 

 of Herr Exner and Herr Auerbach, the possible sharpness in de- 

 finition of the pitch of a tone by an ear of average fineness does not 

 perceptibly increase after sixteen vibrations have occurred. The 

 general results are regarded as confirming Helmholtz's theory of 

 the co-vibration of tone-perceiving organs in the ear. The experi- 

 ments were made w ith a pendulum fitted with a piece of toothed 

 w heel, of radius equal to the length of the pendulum, the teeth 

 impinging on [a piece of cardboard. The continuous tone was 

 obtained from a monchord. 



The torsion of wires of steel, iron, and copper has been 

 recently made a subject of experiment by Herr Warburg ( IViid. 

 Anil., No 5). Among other results, the statically-determined 

 moments of torsion are found to be all smaller than those 

 dynamically determined ; and the differences rise from I per 

 1,000 for steel to 6 for iron and 2S for copper. The elastic 

 pressures seem to increase somewhat more slowly than the de- 

 formations, the divergence being greater for copper than for 

 iron, and for iron than for steel. No dependence of the coeffi- 

 cients of torsion on the tension was discoverable (within the limits 

 of experiment). As to the properties of wires that have under- 

 gone permanent torsion, it appeared that it was only in the case 

 of soft copper wires that, within wide limits of permanent tor- 

 sion, these extend alaiost uniformly over the whole wdre. Con- 

 fining himself to copper wire, then, his experiments lead him to 

 believe that by permanent torsion the wire becomes anisotropic, 

 behaving, at any part, like a crystal of the rhombic system, 

 whose axes have certain directions. 



Attention has been called by Herr Holtz ( IVieJ. Ann., No. 

 5) to an optical illusion in looking at geometrical figures, whereby 

 they appear shorter from right to left than they really are ; a 

 square, i-.^. , appearing more or less as a rectangle, and a circle 

 as an ellipse. One direct consequence is that when we draw 

 such figures according to eye-meaiureraent, we make them to3 

 lon^ horizontally. The reason of the illusion Herr Holtz con- 

 siders to be that, in common life, we much more frequently 

 encounter bodies than geometrical figures, and so are disposed to 

 accept the outlines of such figures for the outlines of actual bodies. 

 Now we see more of a body in a horizontal direction than in a 

 vertical, because we see w ith two eyes, and these are in a hori- 

 zontal line. The outline of a ball appears to us really as an 

 ellipse, because, from right to left, we see more than half of the 

 ball. When we see a true circle this seems horizontally bhortened, 

 because we take it for the outline of a ball, and if we draw a 

 ■circle we unconsciously give the outline of a ball. 



Some researches by Herr Rontgen in the same line as those by 

 Dr. Kerr, revealing a new relation between light and electricity, 

 are described in the Annaleii dcr P/tysik, No. 5 ; the methods were 

 somewhat varied. Special attention was given to the direction 

 of vibration of the light in the liquid, and the author's results seem 

 in the main to confirm Dr. Kerr's views. Dr. Kerr git an effect 



with nitro-benzol only when a spark-interval was introduced in 

 the connection of the one electrode with the conductor of the 

 machine, giving a sudden discharge through the liquid. This 

 Herr Rontgen considers due to the comparatively good conduc- 

 tivity of nitro-benzol ; the spark discharge effects a brief but large 

 difference of potential (not obtained in the other case), producing 

 sudden luminosity in the field of vision. But Herr Rontgen 

 obtained tlie same effect with all the badly-conducting substances 

 he examined ; it w.ns only of longer duration. A welcome 

 method is thus afforded for examining comparatively good 

 conducting'liquids as to electro-optic properties, and Herr Rontgen 

 thus demonstrated, for glycerin, sulphuric ether, and distilled 

 water, an influence of electricity on the transmitted light. The 

 author offers (doubtfully) a different Iiypothe^is of the phe- 

 nomena to that of a durect action of electricity on the light 

 vibration. 



In a recent paper in the Annalen der P/tysik, No. 5, Prof. 

 Clausius criticises recently-published views of Maxwell, Frowein, 

 and Korteweg on the mean length of path of gas molecules. 



PHYSICAL SCIENCE IN RUSSIA 

 W/'E have before us the minutes of the meetings of the Physical 

 ' ' Section during the last congress of Russian naturalists, just 

 published in the last number of the Jonrnal of the Russian 

 Physical and Chemical Society (vol. xii., fasc. 4), and w-e find 

 in them reports of several very interesting papers which were 

 read and discussed during the congress. 



The most numerous communications were on electricity. 

 Thus, M. Eeploff exhibited the new electrophoric machines of 

 his inventi3u. A glass of sulphuric acid is sufficient for main- 

 taining the machine ready, even during moist weather ; it gives 

 very powerful sparks, white and coloured, and succeeds well in 

 decomposing water. — Prof. Khvolson made a communication on 

 corrections to the differential equations of the motion of a 

 magnet which o-cillates under the influence of a metallic tran- 

 quilliser, and discussed the method of computation of corrections 

 to diHerential equations of motion in general. — M. Tchikoleff 

 gives the equations for determining the losses which an electrical 

 cun-ent experiences when passing through telegraphic wires. — 

 Prof. Stoletoff has terminated his experiments for determining the 

 ratio between electro-magnetic and electro-static units (z' of 

 Maxwell). He undertook his experiments in 1876, but had not 

 terminated them at that time ; recently MM. Ayrton and Perry 

 have determined the value of :■ by a method analogous to his 

 own, which differs from theirs in measuring a current produced by 

 a series of successive discharges, by means of a rotating com- 

 mutator, the velocity of rotation of which is mea-ured by means 

 of a chronogi-aph. The preliminary experiments have given a 

 velocity very near to that found by otlier researches, i.e., about 

 300,000 kilometres per second, and Prof. Stoletoff expects to 

 obtain more exact figures.— M. Borgmann continues^ his experi- 

 ments for determining the heating of iron by intermittent 

 mai-netisation. The experiments are very difficult, because of 

 the° inductive currents, but they have already shown that a 

 change in the magnetic state produces an increase of temperature. 



Prof. Lemstrom (Helsingfors) made a communication on his 



most iiaportant work on the causes of terrestrial magnetism. 

 He has demonstrated that an annular isolator, when put in rapid 

 rotation around an iron cylinder, acts upon this last as a galvanic 

 current and magnetises it. Likewi>e an iron cylinder when 

 rapidly rotating in an insulating medium must be magnetised, 

 and thus the earth Vk-hen rotating in an atmosphere of ether must 

 also be magnetised. The various peculiarities observed as to 

 terrestrial magnetism might be easily explained by the motion of 

 the earth around the sun, and by the terrestrial galvanic currents. 



M. Tchikoleff explained his improvements in the Foucault 



electric lamp, which allow several lamps to be placed in one 

 circuit.— Prof. Petrushevsky made an interesting communication 

 on his' measurements of the intensity of the magnetic field 

 between the extremities of electro-magnets of various shapes, which 

 measurements were made for determinmg the best shape to give 

 to eiectro-ma'trnets. That of Ruhmkorff proved to be twice as 

 strong as that of Gramme. The best shape is that of two iron 

 cylinders united together by means of arcs made of broad iron 

 plates. The free ends must be provided with two spherical pole- 

 pieces, each of which has a conical processes, the ends of these 

 two processes being directed one to another. 



In meteorology we notice several valuable papers, the most 

 important of them being that by M. Woeikoff on rainfall in 



