Oct. 20, 1881] 



NATURE 



593 



the higher and the lower parts of the valley, and this is regarded 

 as an imporlaiit factor in the citse ; the cold air above pres-ing 

 on the warm below, and closing the pass to a sort of tube. The 

 ■wind seemed to be active only in the lower parts. 



With the aid of delicate apparatus of recent invention Herr 

 Grunmach ( /Fm/. Ann. Na. 9) has iiivcs'.igated the electro- 

 ma^'neiij rotatijn uf the plane of polarisation uf radiant heat iu 

 solid and liquid substances (flint glass, plate glass, sulphide of 

 carbon, oil of turpentine, distilled water, and alcohol). His 

 findm^ is a^ foil nvs : — 1. In solid as well as in liquid diather- 

 manous bodies there is such rotati m, and always in the direction 

 in which the current flows through the spiral or circulates round 

 the magnetic core. 2. The amount of this rotation i-^, cateris 

 paribus, very different for different substances ; the rotation is 

 greater the greater the index of refraction of the substance. 3. 

 With direct action of a galvanic current conducted round the 

 diathermanous body, the aoioimt of the rotation is proponional 

 to the intensity of the current. 4. In a diathermanous body 

 placed be; u ecu the poles of an electromagnet, the amount of 

 rotation is proportional to the magnetic force acting on the 

 body. 5. The amuunt of rotation increases with the length of 

 tlie substance traversed by the rays ; but the relation between 

 these two qunntiiies could not be nu-uerically determined. 



Experiments on heat-conduction have been lately made by 

 M. Chri tiansen of Copenhagen ( W-'w/. Ann. No. 9), by the 

 following simple method : — Three round copper plates are 

 placed one above another, separate 1 by small pieces of glass. 

 A hole is bored radially into each plate, and a thermometer bulb 

 inserted in eacli h jle. The lowest plate rests on a brass vessel, 

 through which cold water is conducted, and on the top plate 

 le-ts a brass vessel with circuliti m of warm water. Through 

 holes in the two upper plate- (supplied with copjier stop,)ers) tue 

 intervals between the plates may be .filled »ith liquil. M. 

 Christiansen experimented first with air, and he proves that its 

 heai-conductioii increases %\ ith the temperature. The ratio of 

 the conductivity of air to tho e of several liquids was next 

 studied, the liquid being placed in the lower interval. The 

 results agree well with Weber's figures for absolute conductivity. 

 Some experiments were also made with plite glass (dry and 

 wet) and marble. The method may be adapted (the au'.hor 

 points out) to measurement of electric resistances, the potential 

 being measured instead of the temperature. 



Among some interesting experiments with liquid films, de- 

 s.-ribed by M. Plateau to the Uelgian Academy, i> one in which 

 fine iron wire is fir-t bent to represent a six-petalled fl jwer in out- 

 line ; the circular centre being supported on a small fork stuck 

 iu a piece of wood. The wire is slightly oxidised with nitric 

 aci 1. The flower i- dipped in glyceric sjlution, and is then put 

 u ider a bell jar near a window-, so that the sky is reflected in 

 the films. A pretty play of bright colours is soon observed, and 

 it continues for hours. Ag tin, with regard to explosion of soap 

 babbles, one is apt to think the whole of the film is con- 

 verted simultaneously into minute spherules. M. P;ateau has 

 formerly shown that it is njt so, and has analysed the course of 

 the phenomenon. An experiment proving the contraction of the 

 bubble during its qu ck destructimi is as follows : — A bubble of 

 glyceric liquid about li centimetres in diameter is bl iwn with 

 tobacco smoke, and placei on a ri ig. Having waited till the 

 top appears blue, yoit break it there with a metallic wire, where- 

 upon the mass of smoke is shot vertical'y upwards a dozen centi- 

 metres, and then spreads out ho-izontally, in umbrella shape. 

 It then rises more sloAly, and i diffused. 



Prof. Exner of Vienna has lately proved that galvanic ele- 

 ments formed of three elementary sub tances, one of which is 

 bromine or iodine, give perfectly constant ac ion, and that the 

 electromotive forces exactly correspond to the heat values of the 

 cheniical processes. There is no trace of polarisation. Bromine 

 andijdiie are alsi shown to be the wor.st conductors of elec 

 tricity at present known. Both bromine and iodine conduct 

 entn-ely withiut poUrisati m, (the latter in solid as well as in 

 liqui I condition.) The conductivity rises r.ipidly with the 

 temperature. 



Careful experiments by Herr v. Wroblewski on diffusion of 

 liquids (three chloride of sodium solutions and water) are de- 

 scribed i 1 Wied. Ann. (No. 8), and yield the result that the 

 Constant of diffusion (so far as those experiments go) decreases 

 with decrease of the amount of salt, according to a law of simple 

 proportion. The author further tried a photometric_ method of 



measuring diffusion, where the jiroportion of salt is extremely 

 small; using Hufner's specroph otomo'er and (as colouring- 

 matter in water) nigrosin. He cannot claim great exactness for 

 the results, Imt the constant is at least one place of deci.nals 

 smaller th in the smallest constant of a salt hitherto known. 



Dr. Kal[scher, who has been experi nenting on selenium 

 cells for the photophone, confirms the obser\-ations of Adams 

 and Day that li^ht may in certain cases set up in these cells a 

 photo-electromotive force ; the cell becoming its own battery. 

 The same experimenter draws attention to a curious point, 

 namely, that the sensitiveness of seenium cells to light is often 

 greatei^ in cells of high resistance than in those in which, by 

 annealing, the resi-.tance has been gready reduced. A single 

 C--11 kept for some months gradually lessened in resistance, while 

 becoming less sensitive to light. The-e anomalies Dr. Kalischer 

 attribute, to the allotropic modificatijns through which the sab- 

 stance passes, the want of homogeneity accounting also for the 

 photo-electromotive torces observed. 



An excellent paper by M. Gariel has appeared in our con- 

 temporaiy, V Etc-trlcien, in which the formulae for the grouping 

 of cells in a voltaic battery, as deducible from Ohm's law, are dis- 

 cussed and represented in graphic diigrams. M. Gariel has thus 

 arrived at a kinl of abacus by which the variou. problems that 

 arise may be geometrically solved by simple inspecti m. 



Prof. Lovering of Harvard has lately u learthed from the 

 Memoi'-s of the American Academy a paper by Dr. Nathaniel 

 Bo.\ditch of Salem, Mass., communicated in 1815, in which he 

 investigates the figures made by a viouble pendulum which com- 

 pounded two vibrations at rigltt angles to one another. This 

 research, which was illustrated by .several plates of figures, 

 therefore antevla^es that of Lis-ajous, to whom the discovery of 

 these figures is usually accredited, which was pu >li-hed in 1857. 

 Bowditch investigated the cases of the ratios representing unison, 

 the octave, the twelfth, and the double octave. Bowdich was 

 himself inspired to this investigation by a paper writt n by Prof. 

 Dean of Burlington, Vermont, in which a comp 'und pendulum, 

 identical with that known as Blackburn's pendulum, was used 

 to illustra'e the moti ms of the earth as viewed from the mo m. 

 Blackburn's p.-nluluni d ites from 1844. .Sang, in 1S32, used 

 vibrating wires to compound rectangular vibrations ; and Wheat- 

 stone's kaleidophone dates from 1827. 



Self-luminous phjtographs capable of shining in the dark 

 can Ije made, as Eder Ins shown, by layhig a transparent 

 " positive" upjn a sheet of Balmain'.s luminous paint, and then 

 exposing the latter to sunlight. The photograph thus produced 

 is a "positive" also. It lasts, of course, only f r a limited 

 time. 



Dr. MiJLLER-ERZBACH, who has just made an exhaustive 

 ex.imi nation of the desicca'ing powers of different substances, 

 states that there is no perceptible difference lietween the power 

 of coiicentrated oil of vitriol, glacial ph jsphoric acid, and solid 

 cau-tic potash in this re-pect, and that caustic sola an I chloride 

 of calcium are only slightly inferior, the difference in tension of 

 aqueous vap lur between ]ihosphoric anhydride and anhydrous 

 chloride of calcium being a fraction of a iiiillinietre in the baro- 

 metric c )luum. He alsj states that caustic s ida is absolutely 

 dehydrated by being shut up in a desiccator with caustic p jtash. 



SOLAR PHYSICS ■ 



LiEUT.-CoL. Donnelly, R.E., made the following intro- 

 ductory remarks to Prof. Stokes' fir^t Lecture which was the 

 fir>t of the series : — 



I greatly regret both for your sake and my own that I should 

 have to detain you for a few minutts from the lecture which we 

 have all come to hear. It has, however, been c msi lered d -sir- 

 able that s jme explanation should be given of whit has led to 

 the formation of this Commitee on Solar Physic-, anl what has 

 led t J the giving of these Lectures. I am glad to say that in 

 engiging your attention for a few minutes I shall not seriously 

 curtail the time that Prof. Stokes will have at his di-pisal, for 

 he has been good enough to undertake to lecture on Friday in 

 plice of General .Strachey, who unfortunately cannot give the 

 lecture w hich has been announced for him. 



• Introductory Lecture by Prof. Stskes, F.R.S., in the South Keo 

 [useum Theatre on Wednesday, April 6, 1881. 



