6i« 



NATURE 



lApril 2^, 1 88 1 



M. LONGUININE has recently determined (in Compl. rend.) the 

 heats of combustion of various alcohols of the allyl series, and 

 compared the numbers with those expressing the heats of com- 

 bustion of metameric aldehydes. He finds very marked differ- 

 ences between the two series of numbers, showing once more a 

 distinct connection between the energy lost by a carbon comp jund 

 in passing from one state to another standard state, and the struc- 

 ture of the molecule of that compound. 



M. Berthelot, in continuation of his researches on com- 

 pounds of metallic halogen salts with haloid acids, describes in 

 Compt. rmJ. the action of gaseous hydrochloric and hydrobnmic 

 acids on alkali chlorides and bromides ; he shows that the i/aseous 

 acids are absorbed by the dry salts with disengagement of heat, 

 and that the products of the actions are prossessed of properties 

 which distinguish them from mere mixtures. 



M. Berthelot also considers the reciprocal actions between 

 alkali haloid salts and haloid acids; he shows that as a rule 

 alkali chlorides are decomposed by hydrobromic acid, but that 

 in some cases and under special conditions of temperature, 

 bromides are decomposed by hydrochloric acid. The general 

 results are shown to be in keeping with the laws of therujo- 

 chemistry. That action in which most heat is evolved occnr-, 

 but the products of the action may be unstable under experi- 

 mental conditions, and hence the primary change may be mudified, 

 or even reversed. 



M. MuNTZ states that his investigations have shown that 

 traces of alcohol exist in all natural waters, whether rain, river, 

 sea, or snow water. He de-cribes his method of applying the 

 iodoform test for alcohol, whereby one part can be detected in 

 1,000,000 parts of water. 



PHYSICAL NOTES 



_M. Laurent of Paris has constructed "magic mirrors" 

 giving similar effects to those brought from Japan, but of glass 

 silvered at the back instead of metal. By engraving patterns at 

 the back and silvering the front surface, the mirror has a per- 

 fectly plane surface only when the air-pressures at the front and 

 back are equal. If the air behind be compres-ed or rarefied the 

 tliinner parts will have relatively a greater convexity or concavity 

 than the rest, and in the disk of light which the mirror reflects 

 on to a wall from a luminous point the pattern engraved on the 

 back v\ ill accordmgly appear dark or light. 



From experiments on the radiation and conduction of heat in 

 rarefied gases ( Wied. Ann., No. 13) Herr Graelz finds the re-ulis 

 in much better agreement with Stefan's law cf radiation than 

 with that of Dulong and Petit, and "ft may be affirmed that in 

 the temperature-interval from 0° to 250° C. the radiation is very 

 nearly proportional to the fourth power of the temperature." 

 The factor of proportionaluy a (in Stefan's formula Q = aT^) is 

 then that amoujit of heat which is radiated from one squ.ire 

 centimetre of a substance of - 272° C. in a second towards a 

 space of the absolute temjjerature 0° (- 273°). By the meth. d 

 of least squares Herr Graetz finds 



.r for glass = I '0846 " " gra mme centigrade ^ 

 centim. seconds 

 Certain divergences at low temperatures suggest that while the 

 intensity of radiation grows with rising temperature, it perhaps 

 grows differently for different heat colours. 



In a recent communication to the Munich Academy, Herren 

 Nies and Winkelmann decribe an inquiry into the volume- 

 changes of various metals in solidifying. Of eight nietajs 

 examined, six (viz. tin, zinc, bismuth, aniimony, iron, and 

 copper) were pr.jved to undergo expansion in passing from the 

 liquid to the solid state. F.jr three of the metals approximate 

 values for the amount of this expansion were obtained (tin 

 showed an expansion of 07 per cent., zinc 0'2, and bismuth 3). 

 Two metals (lead and cadmium) gave doubtful results; but ilie 

 nuthors find some reason to believe that they aUo expand in 

 solidifying. So far then the rule would appear to be general for 

 metals. 



M. TRfeVE describes in the Comptes nndus some curious 

 observations from which it would appear that when light is 

 admitted from a natural or artificial source through a slit, more 

 light passes if the slit be horizontal than if it be vertical. M. 

 Prc-ve has produced photographs taken behind slits in various 

 positions to prove that the effect is not an illusion of the 



eye. The phenomenon appears to us inexplicable, but certainly 

 requires further proof to substantiate its reality. 



M. Mercadier still continues to study radiophonic pheno- 

 mena. He finds it possible to increase the effects by uniting in 

 one tube the vibrations of several receiving disks. He also.finds 

 it possible to consiruct tubes whose length corresponds to the 

 wave-len'/th nf ihe vibrations radiophonically excited, and which 

 respond to the note emitted. M. Mercadier hopes by these 

 means to re-delermine with increased accuracy the velocity of 

 sound in air and other gases. 



With regard t.> the beats and beat-tones of harmonic intervals 

 Dr. Koenig argues ( m,d. Ann. No. 3) against Prof. Helmholtz's 

 view, that ihese are due to harmonic tones of the lower primary 

 sounding witti the his;her(r)r Koenig, in his former experiments, 

 having u-ed strongly-excited tuning-forks). He shows how the 

 phe .omena may be studied with the aid of a "wave-syren," in 

 which a idast of air is sent through a slit against the serrated 

 bolder of a r>>tating disk, or of a ring-section of a thin cylinder. 

 He has the border of the disk cut to represent accurately the 

 curve produced by combination of the curves of two simple tones, 

 givins; an air motion, when blown against, quite like that from the 

 two tones sounded together. The beats and beat-tones are then 

 heard. With a mere wavy outline for the border and the slit at 

 right angles one hears a quite simple tone, v\hich however is at 

 once changed to a " clang " with srong overtones, when the sHt 

 is slanted a little. Nnw, with two simple tones got thus the 

 beat-tone heard when the slits are at right angles should (on Helm- 

 h dtz's supposition) be less distinct than when, the slits being 

 slanted, the overtones are brought out ; whereas the reverse is 

 the case. 



Dr. Koenig, in the same number, describes a simple lecture- 

 apparatus for producing heat-tones. It consists of two glass cads 

 of ilifferent length, clamped in vertical position by the middle to 

 a j linted frame, which, through an elastic contrivance, keeps 

 their lower ends pressed against the cloth-covered periphery of a 

 wheel which di s in water in a trough. The friction calls forth 

 the longitudinal tones and the beat-tone. 



An improved form of the Tdpler air-pump has been devised 

 by Herr Bessel-Ilagen ( /K/cv/. Ann. No. 3), with which con- 

 siderably hi;;her vacua can be reached than those Mr. Crookes 

 obtains with the more complicated and fragile Sprengel-Giming- 

 ham apparatus. The average limit of rarefaction was found to 

 be ^ millionths of an atmosphere (-^^ in one case), while the 

 other pump only gives iV millionth. (It is noted that Prof. 

 O.den Ro. d has obtained -5^, and in one case even ^^-j^ with a 

 modified Sprengel.) With his highest vacua the author found 

 electriciiy to jia^s (using plate-electrodes and a strong Holtz 

 machine, with Leyden jars). He considers mercury-vapour an 

 insulator for electricity ; but shows that radiometric movements 

 depend greatly on its pres-ure in vacuo. No diffusion of 

 hydrogen through the glass could be detected. 



An artificially- formed body showing polar effects in the way 

 of attraction and direction is produced by Herr Holtz ( IVied, 

 Ann., No. 3) thus : To one end of a short glass rod is cemented 

 a plane piece of glass, and to this a short narrow glass tube (in 

 a line with the rod). In the tube is placed a sewing-needle 

 1' nger than it, and carrying at its head a thin pasteboard disk 

 (22 mm. across), which has attached on one half of its peri- 

 phery, reachintr over both above and below, a pasteboard strip 

 (10 m 11. broad) ; opposite this, on one of the surfaces, is fastened 

 a small projecting point of tin-foil. Brought between hollow 

 disks fixed to the rods of a Holtz machine, the tin-foil point 

 always turned to the positive pole. Next, the glass rod with its 

 disk v\as attached to the end of a light horizontal glass tube, 

 hung bifilarly, and so brought between the hollow disks. The 

 disk first turned into position, and was then attracted towards 

 the negative p le. The phenomena are thought to illustrate 

 unipolar conductivity. 



The simple tourmalir.e-pincette, by reason of its small field, 

 can be used with only a small number of crystals. To enlarge 

 the fiel'l M. Berlin has applied to it a part of the lenses of the 

 polarising microscope. This, it is known, consists, first, of a 

 polari-er and f icus ; second, of a microscope and analyser. The 

 polariscr and analyser, at the extremities, are pretty large jiece-', 

 and if replaced by two tourmalines placed betw-een the focus and 

 the microscope (of simplified form) the apparatus is rendered 

 much smaller and handier. This is the principle of M, Berlin's 

 new tourmaline-pincette (of which details will be found. in the 



