Sept. 29, 1 881] 



NATURE 



5^1 



occasrion to carry back to a distaut epoch the place of a star not 

 included in Dr. Danckwortt's list. The values of the arcs A, 

 A', and 6, are given for the beginning of every century within 

 the above period. The place of the present Pole-star for the 

 year - 2COO is found to be R.A. 335° lo'o", Decl. +67° 34' 30". 

 We may mention that the formulas for the reduction of the 

 places of stars to distant epochs are inveaigatid in a very 

 interesting paper by Prof. Schjellerup, w hich Dr. Copeland and 

 Mr. Dreyer have translated in No. z of Copernicus, and which 

 the reader ^\ ho desires to acquaint himself with the application 

 of the rigorous method of taking account of precession should 

 couult. 



PHYSICAL NOTES 



The conducting power of metals for heat and electricity has 



lately occupied several physicists. Prof. Lorenz of Copenhagen, 



employing two methods [IVied. Ann., No'. 7 and S), gets the^e 



results : (I) for the better conducting metal-;, a confirmation of 



Wiedemann and Franz's law, that the ratio of the two conductivi- 



tie.', both at 0° and at 100° is nearly constant ; in the inferior 



conductors it increases much with decreasing conductivity ; (2) 



k k 



in all metals except iron, the ratio -L"" ; — i' is constant, and ap- 



proximately equal to I '367 {k and k denoting the conductivities 

 for heat and electricity respectively). Thus, for absolute tem- 

 perature T,-=Tx. constant. 



K 



A " MEDICAL hydrotelephone," contrived by Prof. Sabatucci 

 {Hiv. Sci. Iitd.) is of the following nature : — Two lead cylinders 

 (Sctm. in diameter and 4ctm. thick) are closed each wih two 

 very fine iron lamina'. To the anterior \ art of each is fitted a 

 wooden mouthpiece (like that of a Bell telephone) connected to 

 a caoutchouc tube, thiough which one may hear at a distance. 

 The posterior part has a very sensitive electromagnet communi- 

 cating with a microphone and battery. One tube is applied to 

 either ear. Words or sounds produced before the microphone, 

 and heard but faintly, are rendered intense and distinct by intro- 

 ducing liquid into the cylinders (the less dense the liquid the 

 better). Two sounds may be compared, and their intensity 

 exactly measured, by varying the quantity of the liquid and 

 noting the eflfects throuyh the tubes. Various applications of the 

 apparatus, in clinical medicine esj. ecially, are looked for. 



The effects of lightning on trees placed near a telegiaph \iire 

 are forcibly illustrated by phenomena lately observed by M. 

 Montigny {Bull. Bdlg. Acad., No. 7) oir a portion of the road 

 from Kochefort to Dinant ; which runs from east to west, first 

 on level ground and between poplars for about 1500 metres, 

 then rises gradually 61 metres through wocds to a wooded 

 plateau some 2CO metres in extent, then comes down to another 

 plain. Of the pop ars bordering the road on either side those 

 on the north side, next the telegraph line, have largely suftered, 

 80 out of £00 having been struck, or about a sixth ; those on 

 the other side are very rarely struck. I he plain presents only 

 one case, and that doubtful. The instances nmltiply \\ ith in- 

 creased elevation, and in the wooded plateau on the top reach a 

 maximum (64 per cent.). The most violent discharges have 

 been on the we-t side of the plateau and rising ground, which is 

 generally first reached by the storms, and the injuries to trees 

 are mostly opposite and under the level of the wire. M. Mon- 

 tigny supposes that \\ hile the wire is strongly electrified by in- 

 duction, the lightning does not striUe it, on account of its 

 relative insulation, tut strikes the neighbcuring poplars directly, 

 which, wet with rain, afford an easier passage for the electric 

 fluid to the ground. 



M. PiCTET has examined seven varieties of steel (chiefly from 

 a Sheffield and a Vienna house) with regard to magnetic power 

 (Arch, dcs SciciictS, August 15). This power he finds to depend 

 on the presence of carbon in the iron, and the aggregation of 

 these substances. One of the two steels giving the best results 

 had |th per cent, of carbon. Samples with i4 and l^th per 

 cent. V ere inferior. German steel of poor quality (for springs) 

 yet made a good magnet ; it had little homogeneity, and con- 

 sisted of an intimate mixture of iron, and iron cemented with a 

 small proportion of carbon. A too-small proportion of carbon 

 suppresses or weakens the remanent magnelisni. M. Pictet also 

 finds that the increase of magnetic power in a magnet through 

 the mere presence of the armature in contact is a certain fact for 

 some qualities of steel, but not for all. The first magnelic 



passes develop nearly the w hole of the remanent magnetism in 

 all artificial magnets. Detachment of the armature by the dyna- 

 mometer seemed to have no action on the magnetic pow er, only 

 the slipping of the armature when near rupture must be avoided. 



An experimental inquiry into the production of tones by pas- 

 sage of gases through slits is described by Herr Kohlrausch in 

 Wiediiiiaiin's AnnaUn (No. 8). The principal results are these : 

 (I) For all widths of slit between 0-2 mm. and 1 mm. and all 

 densities of gas employed, the pitch « may be represented as 

 linear function of the velocity of outflow u by the formula « == >6 

 (« - "0)1 " here «(, and k are constant for a given width of slit 

 and variety of gas ; (2) wTth increaing width of slit (o'2 mm. to 

 I mm.) «„ decreases, k increases ; (3) «„ and k (for air) are as 

 good as independent of the thickness of the slit (i.e. the thick- 

 ness of the brass plates forming it), fr. m i mm. to 9 mm. ; (4) 

 with increasing density of gas (07 to I "5) «„ generally decreases, 

 k increases, i.e. the tone?, ceteris paribus, become higher ; (5) «„ 

 and k depend in no suiall measure on other properties of gases 

 be. ides density ; (6) starting from wide slits with constant 

 velocity of outflow, the pitch increases pretty uniformly with 

 narrowing of the slit, reaches a maximum with widths between 

 035 mm. and 0'27 mm. — with thicker slits, smaller pressure", 

 and less dense gases, sooner than in the opposite cases — and 

 then decreaes more and more quickly with the width of slit; 

 (7) this maximum pitch characteristic for eacli velocity of out- 

 flow occurs with a greater width of slit, the less the velocity. 

 From a comparison with Strouhal's experiments on the tones 

 excited by motion of cylindrical br.dies in air, the author concludes 

 that the production of slit-tones is to be refen-ed toUke causes to 

 those of wire-tones. 



An electrophotometer recently described by Dr. Nachs (La 

 Natura, August i) has the following arrangement : — A wooden 

 case oj- ening on one side and above is divided into two compart- 

 ments, an upper and a lower. The lower contains in the inner 

 part a dry pile of 200 elements, and iu the outer a Jacobi rheo- 

 stat, the cylinder of which has thirty windings (the number 

 introduced into circuit by turning a handle is precisely indicated). 

 The upper compartment has interiorly a g.alvanometer, and e.\- 

 teriorly an adjustable truncated cone with inner surface black- 

 ened, and within it a small selenium cell similar to those used 

 by Bell and Tainter, to receive the light. This cell and the 

 three other electrical instiumtnis are connected by wne. Tlie 

 mode of actijn will be readily comprehended. 



Mr. Mil.ne has observed (Zeils. f. Kryst.) that if a sus- 

 pended quartz ball be allowed to impinge in various ways upon 

 a fixed ball of lime spar, or if the ball of Inne spar be placid 

 on a billiard table and the distance observed to which it is driven 

 by the shcck, in the former case the quartz ball rebounds fiu-thest, 

 and in the latter the lime sp.ir ball is driven furthest, when the 

 im, ulse is in the direction of the (crystalline) axes. 



In a paj er to the Bremen Society of Natural Science, Herr 

 Miiller Erzbach describes experiments in which he sought to 

 ascertain the relative tension of aqueous vapour over saturated 

 solutions of different hygroscopic substances, the inclosed air 

 being submitted for long periods to the action of the.se. I. 

 For saturated solutions one finds in the same series, soda, potash, 

 chloride of calcium, an increase in the vapour-tensions, and a 

 decrease in the contractiins. 2. Phosphoric acid anhydride, 

 oncentrated sulphuric acid, and hydrate of potash deprived of 

 water, present no essential difference in attraction of water. 3. 

 Caustic s< da and chloride of calcium, with small proportion of 

 water, difler little in attraction of water, but they do not 

 bind it so firmly as phosphoric acid or hydrate of potash. 4, 

 Hydrate of soda can be completely deprived of water by in- 

 closure with hydrate of pjtash. 5. The difference in tension of 

 aqueous vapour over the anhydride of j-hosphoric acid and 

 chloride of calcium nearly without water amounts to only a 

 small fraction of a millimetre of mercury. 



The hypothesis that the lutniniferous ether is at rest and the 

 earth moves through it, has been lately put to experimental test 

 by Mr. Michaelson of the U.S. Navy (Amer. Journ. of Science, 

 August). Two pencils of light which have travelled over paths 

 at right angles (one path being in the direction of the earth's 

 motion) are permitted to interfere. On rotation of the apparatus 

 90° a measurable displacement, estimated at about one-tenth of 

 the distance between the fringes, might be looked for (the 

 author considered) if the hypothesis of a stationary ether were 

 I correct. The apparatus was first tried in the Physical Institute 



