3o: 



NA TURE 



{Jtily 2g, i8So 



ordinary steam-enjine piston. This principle is not new, having 

 been employed by Paje, Bourbouze, and Du Moncel in the 

 construction of electro-motors. The novel point however about 

 the motor of M. Deprez is that the magnetism of the soft iron 

 core is never either reversed or interrujited. This was the weak 

 point of the earlier machines, but it has been obviated in the 

 new form by the device of dividing the solenoidal coil into 

 sections like the separate coils of the ring-armature of the 

 Gramme machine, the current being thus transmitted first to one 

 part of the cylindrical coil and then to anotlier. The commutator 

 which distributes the current successively to the various sections 

 is worked by an excentric on the shaft of the fly-wheel in the 

 ordinary way, but the "lead" does not require to be so much as 

 a quarter of a revolution. 



The phenomena of explosion of bombs by freezing of water 

 (once studied by Major Williams at Quebec) have been further 

 elucidated by Prof. Hagenbach of Bale (Arcki-jcs dcs SciciUiS, 

 June 15), who exposed, last winter, two iron bombs 15 ctm. 

 exterior diameter and 2'2 ctm. thicknes=, filled with water and 

 closed by screw stoppe.-s, at temperatures descending to - 20°. 

 One bomb, placed out early in the afternoon, burst next mornin:; 

 about 7 ; the other, exposed about 10 a.m., exploded about 

 9 p.m. In the latter case the stopper was violently projected to 

 a distance and could nov.-here be found (the spotless' snow around 

 would have soon revealed its position, if anywhere near). Some 

 parts of the screw thread were detached ; there were several 

 fissures round the orifice, and a cylinder of striated ice was forced 

 out, having an irregular top and a curious upward cun-ed fila- 

 ment of ice attached, narrowing from 9 mm. to 3 mm. diameter, 

 and flattened on its upper concave surface. It is thought a little 

 water in suspension got out by the first opening in the screw, 

 flowed down the bomb, and froze ; its freezing provoked crys- 

 tallisation of the whole mass, and the stopper was expelled, the 

 ice following and lifting the attached frozen vein. A little later 

 some water within the expelled cylinder probably froze and burst 

 the top of this cylinder into four pieces, which twisted like 

 petals, causing the filament to turn upwards. The other rase 

 was perhaps even more curious. The stopper was not thrown 

 out, bat the bomb burst, a trianguhr piece next the stopper 

 being raised. A round filament curving downwards was here 

 found attached to the protruded ice, and it had some sixteen 

 enlargements or nodes, equidistant 7 mm. The initial jet of 

 water had probably come out with high velocity and straight 

 course, and been solidified, afterwards curving down by the 

 action of gravity. The nodes w-ere doubtless due to the vibratory 

 motion obser\-ed in liquid veins. 



In a recent paper to the Vienna Academy (June to), Prof. 

 Reitlinger and Dr. Wachter throw some new light on the nature 

 of "electrical ring-figures." They consider these to arise from 

 two causes not clearly perceived before ; first, a disruption of the 

 metal, w ith projection of solid, fused, and vaporised particles fiom 

 it by positive electric potential alone ; and second, an electro- 

 chemical decomposition of aqueous vapour present in the atmo- 

 sphere in which tlie figures are produced, between point and 

 plate. To the first-named cause is due the disruption disk 

 (Aufn-issiitigsc/ieibe) in the centre of positive or mixed figures, 

 and appearing oxidised in air, but met.il-bright in hydrogen (it 

 affords a new mode of distinguishing poitive electricity from 

 negative). With a strong spark (from a Ruhmkorff strengthened 

 with a Leyden jar) the authors got dispersion and condensalioii 

 ?-;«_o-j round the disk, presenting various metallic colourings indi7 

 hydrogen. To the second cause (electro-chemical decomposition 

 of water-vapour) are attributed the various-coloured oxide rings, 

 giving tlie ring-figures observed by Priestlev, Nobili, Grove, 

 Riess, &c., and Peterin's brigfit disks. The former occur where 

 positive, the latter where negative, electricity passes from the 

 plate into the air. Thus all the ring-figures observed consist of 

 four "form-elements," viz. (i) central disntption-disks ; (2) 

 oxide rings ; (3) bright disks; and (4) dispersion and condensa- 

 tion rnigs. It is further found that all these kinds can be altered 

 in form by a magnet. 



ACCOKDING to the dynamical theory of gases it is probable 

 that the exponent characterising the relation of the coefficient of 

 diffusion to the absolute temperature is higher by unity than in 

 the case of coefficients of internal friction. This has been fully 

 confirmed by experimen's of Herr v. Obermayer (Wien. Akad. 

 -4«:., May 7), which give, for permanent gases, approximately 

 Ml for coercible 2 (the lower exponents being -J and I). The 

 experiments extended over too fe^^• gas-mixtures to determine how 



the exponent is affected when a coercible and a permanent gas 

 difluse into each other. 



Don Edu.vrdo Lozano of Teruel, Spain, has lately pub- 

 lished a modest little volume of ninety pages, entitled "Estudios 

 Fisicos," in which some of the more recent advances in physical 

 science are explained in an easy and popular form. Amongst the 

 topics are the blue of the sky, the mechanical equivalent of 

 heat, atmospheric electricity, &c. It is interesting to observe 

 such signs of a revival of interest in the physical sciences in 

 Spain. It is somewhat of a novelty to find the names of Mayer, 

 Ilirn, Wells, Dove, and Tyndall in a Spanish treatise ; and w^e 

 draw a good augury from this sign that these names have ah-eady 

 penetrated into a country where science has unfortunately been 

 so long at a low ebb. 



A BuNSEN burner of modified form has been contrived by M. 

 Terquem which promises to be well adapted for spectrum work 

 and for producing monochromatic light. Instead of the usual 

 two lateral apertures to admit air, the air is allowed to penetrate 

 between the foot of the lamp and the base of the vertical tube, 

 which is for this purpose raised 6 or 7 millims. above the solid 

 foot. The top of the tube is divided into four by a couple of 

 vertical partitions, so that instead of the usual central cone in 

 the flame there are four cones. It is claimed for this flame that 

 it i; more solid, and that the temperatures throughout the dif- 

 ferent parts of the flame are more nearly equal than in the usual 

 Bunsen burner. To procure monochromatic light it suffices to 

 place a small fused bead of sodic chloride between the four 

 central cones of flame. 



Following out his recent discoveiy that the prolonged action 

 of the actinic rays upon a sensitised photographic plate produces 

 a reversal of effects, M. Janssen has obtained some interesting 

 results. He has by direct exposure taken a positive photograph 

 of the sun 10 centims. in diameter, showing the spots in their 

 usual dusky tints. He has, after exposures varying from one 

 hour to three hours, obtained perfect positives of landscapes. 

 A view of the park of Meudon thus photographed shows the 

 sun as a white round spot upon a dark sky. Moreover, from 

 such positives other positives can be printed by prolonged ex- 

 posure ; and it is now possible to obtain negative prints of 

 negatives by the same simple expedient. M. Janssen promises 

 at an early date a complete and searching memoir on the whole 

 subject of photography in relation to the different rays of the 

 spectrum. 



Ax electrical stone-breaker is the latest American invention. 

 A dynamo-electric machine furnishes the power to an electro- 

 magnetic chopper capable of delivering from 1,000 to 2,000 

 blows per minute. Stone-breaking requires the exertion of very 

 great forces through very small distances, in fact precisely the 

 kind of work for which electro-magnetic machines on a large 

 scale might be expected to be successful, if only the cost_of 

 generating the electricity were not so serious. 



In a recent valuable paper on the thermal and optical be- 

 haviour of gases under the influence of electric discharges ( ll'icd. 

 Ann., No. 6), Herr E. Wiedemann first studies the thermal 

 phenomena in the case of discharges of the influence- 

 machine, and indicates a different behaviour of the positive and 

 the negative electricity. He then describes an experimental 

 attempt at numerical determination of the quantities which pro- 

 duce a change of the band-spectrum of hydrogen into the line- 

 spectrum. He further investigates the nature of the discharg:: 

 from the negative electrode in greatly rarefied space. Then he 

 discusses the applicability of other electrical sources, inductoria, 

 large galvanic batteries, and Leyden jars, to spectrum-analytical 

 researches, also the continuous and discontinuous discharges in 

 gases. The paper concludes with theoretical considerations as 

 to the phenomena of discharge in gases and the nature of 

 spectra. 



The known abnormal variation of density of mixtures of 

 acetic acid and water suggested to Herr v. Reiss {IFird. Ann., 

 No. 6) a means of ascertaining whether there were any per- 

 ceptible relation between the densities and specific heats. He 

 finds that, unlike solid bodies, those mixtures show in general, 

 with increase of density, a proportional increase of specific heat. 



An example of anomalous dispersion by a glowing vapour, 

 viz., that of sodium, has been recently observed by Herr Kundt 

 (IVicd. Ann., No. 6). lie was prep.aring for a lecture the 

 well-known experiment of reversal of the sodium line, and per- 



