442 



NATURE 



\_Marck lo, 1881 



placed at the vertex, and comparing it with his result, deduced 

 for the mean density of the earth the value D = 577. If how- 

 ever the accepted density of the earth as determined, by Bailly 

 at 5 67 be adopted, it foUows that the mean density of Fujiyama 

 is only 2'oS. 



A CAPITAL summary of the recent thermochemical investiga- 

 tions of Julius Thomsen appears ia the current number of tlie 

 Am. Journ. Sci. from the pen of Prof. Josiah P. Cooke (of 

 Cambridge, Mass.). The peculiar significance of these researches 

 in their bearing upon the problems of molecular structure in 

 general and upon the supposed ring-structure of the benzene 

 molecule in particular, is pointed out in a clear and emphatic 

 manner. 



M. RosENSTlEHL has freshly determined the tints correspond- 

 ing to the three primary colour-sensations, on the principle of 

 rotating disks originally devised by Clerk-Maxwell. Constructing 

 a disk with seventy-two sectors of gradating tints of as nearly 

 equal saturation as could be judged of by the eye, he found that 

 a sensation of red more powerful than any single red tint could 

 be compounded from blue, violet, red, orange, and orange-yello«-, 

 with a maximum intensity in the orange. Similarly a sensation 

 of green more powerful than the brightest green tint, could be 

 compounded out of a set of tints having a greenish-yellow for 

 their maximum point, and the sensation of blue culminated in a 

 tint named " third blue " by M. Rosenstiehl. Hence M. Rosen- 

 stiehl proposes to accept as the primary-sensation tints of the 

 Voung-Helmholtz theory the orange, the yellow green, and the 

 (" third ") blue tints, in which the three sensations of red, green, 

 and blue find their respective maxima ; further arguments on this 

 point are promised shortly by M. R::senstiehl. 



According to Wiedemann Swedish filter-paper, pyroxylised 

 by steeping in mixed strong nitric and sulphuric acids, forms an 

 excellent source for electricity by friction. Prof. Guthrie's films 

 of collodion and gutta-percha, in five or six alternate layers, 

 realise the same end, namely that of utilising for the generation 

 of electricity the most powerfully ticgativc electric known 

 pyroxylin. 



During a hailstorm in Geneva on January 19 Prof. Colladon 

 observed the hailstones as they fell to repel each other mutually 

 and to bound about after lying quiet for a moment or two on the 

 ground exactly after the fashion of the pith balls in Newton's 

 well-known experiment of the electric hail. The observation 

 would appear to have a bearing on Volta's somewhat neglected 

 theory of the formation of hail. 



Commander O. J. Sherm.\n has taken some observations of 

 deep-sea temperatures during the summer of iSSo on the Arctic 

 steamer Guliiare, when becalmed at about lat. 61° N., long. 56= 

 W., at a point where a branch of the warm Gulf Stream current 

 is represented on the maps as being overlapped by an Arctic 

 current w-hose direction is to the eastward coast of Greenland. 

 The temperatures at the surface being in two observations 

 respectively 4l°'9 (F.) and 45° 'o, those at the depth of sixty 

 fathoms were found to be sg^'o and 40°'o respectively. At 150 

 fathoms a temperature of 3S°'2 was observed, but at lower 

 depths the temperature was again higher, reaching 40° 'S at 300 

 fathoms. 



M. Paul S£guy, whose experience as a constructor of 

 vacuum-tubes is very great, gives the following results of obser- 

 vation upon the effect of cold upon the discharge through 

 exhausted tubes. A tube cooled (naturally by being placed in 

 a cold room) exhibits increased resistance, sometimes double its 

 usual resistance, and may even require to be warmed at the fire 

 or over a spirit-lamp to bring it to its usual working condition. 

 But then the tube does nDt at once recover itself, but only 

 gradually as the passage of the spark liberates heat and warms 

 the glass and the electrodes. This experiment is best shown 

 with a long thin tube and with a feeble induction-coil. With 

 Crookes's high-vacua tubes the effects of heat are more pro- 

 nounced, and can be readily observed by arranging a discharger 

 in a branch circuit, the spark leaping between the poles of the 

 discharger when the air-resistance is less than that of the tube. 

 A c )oled Crookes's tube does not transmit a spark equivalent to 

 a 3-centimetre spark in air; but when warmed, the "radiant'' 

 effects appear to give place in turn to ordinary stratified dis- 

 charges as the temperature rises. The inverse order of pheno- 

 mena should take place on cooling, but does not if care has not 

 been taken in the construction of the tube to expel residual 

 occluded ga-es from the aluminium electrodes by heating them 



during the exhaustion. The effects of extreme artificial cold 

 upon vacuum-tubes was not tried by M. Seguy. In conclusion 

 M. Seguy asserts the existence of a curious phenomenon, namely, 

 that in a tube used frequently and for a long time, the vacuum 

 may grow more perfect, so as at last to be almost absolute. M. 

 Seguy attributes this effect to the gradual occlusion by the 

 electrodes of the residual gases. 



It has been proved by Herren Strouhal and Barus ( Wied. 

 Ann., No. 13, 18S0), from experiments in which steel wire was 

 treated so as to show all degrees of hardness bet" een the glass- 

 hard and annealed states, that the thermo-electric and galvanic 

 properties of steel vary with the degi'ee of hardness in a very 

 sensitive manner. Their researches throw some useful light on 

 the nature of the annealing process and on the magnetic be- 

 haviour of steel in relation to its hardness and other properties. 



Herr Holtz has been able [JVied. Ann., i. 1S81) to measure 

 the nloduIu^ of elasticity of rods of carbon used for the electric 

 light (Carre's, of Paris) by the acoustical method ; the rod being 

 held in the middle with two fingers, and stroked lengthwise 

 with two other fingers on which colophouium has been rubbed. 

 The modulus increases with the density, which is, as a rule, 

 greater m the thinner rods. The tone of thin rods alters a good 

 deal, on repeated rubbing, through heat being generated. On 

 an average the modulus is equal to that of lead. As to the 

 proved increase of electric conductivity of carbon rods with rise 

 of temperature, Siemens has tried to account for it by supposing 

 allotropic modification (as is probably the case with selenium) ; 

 Herr Holtz, however, shows that pyrolusite, a metallic oxide, 

 behaves similarly, but such an explanation would not here apply. 

 Nor does pyrolusite conduct as an electrolyte; there is no 

 polarisation. For carbon Herr Holtz adheres to his hypothesis 

 (of closer pressure of molecules caused by heat, improving the 

 conduction^, in default of a better. 



A centigrade photometer devised by S. Coglievina is de- 

 scribed in the Rivista Sci. Ind. for January 31. He seeks to 

 remedy the imperfections of ordinary methods by substituting for 

 a single source of light, defined by the substance of the com- 

 bustible or its hourly consumption, a flame of variable size, 

 which can be reduced to a particular- degree of illuminating 

 force. He means to apply the same principle to the electric and 

 other light sources. 



An interesting phenomenon of polarisation of light was 

 observed by Herr Sorrensen in the recent cold weather (Maturf., 

 No. 9). Some of the ice on a window-pane had melted, the 

 water forming a small pool at the bottom. In this pool various 

 bright arrd beautiful colours appeared ; on looking closer they 

 wer-e seen to be only in the grotesque images of frost flowers on 

 the lower part of the w indow, reflected in Jthe wafer. The 

 reflecting water surface was here the analyser, while the thin ice 

 cry.rtals, varying according to position and thickness in the ice 

 flowers, played the part of polychromatic gypsum and mica 

 plates. To find the polariser Hen- Sorrensen took a Nicol prism, 

 and observed that the daylight it-elf was strongly polarised ; and 

 this he accounts for -by the presence of a light mist of ice 

 particles reflecting the sunlight. The temperature outside was 

 about - 12°. 



With reference to the physical conditions of heavenly bodies 

 Herr Lohse (Wicd. Ann. l) has experimentally studied the 

 phenomena of glow on various metallic electrodes (magnesium, 

 zinc, iron, cadmium, copper, &c.) ia a hydrogen atmosphere of 

 varying pressure. Quantitative data as to the relation of vapour 

 formation to the density of the gas are furnished ; and it is 

 proved, inter alia, that with progr-essive rarefaction of hydrogen 

 the luminous power of metallic vapours in the more refrangible 

 parts of the spectrum increases (a sign of exalted temperature). 



M. Pellat gives, in the Journal de Physique (February), 

 results of an inquiry into the apparent 'difference of poten- 

 tial of two metals in contact. This difference he finds to 

 depend essentially on the nature of their superficial layer, and 

 to vary (sometimes considerably) with chemical or simply physi- 

 cal changes of the surface. When an inert gas surrounding the 

 metals is rai-efied, the apparent difference of potential increases, 

 and it recovers its former value on the pressure being restored. 

 Further, the said difference has the same value as the electro- 

 motive force of a battery element formed by alcohol and the 

 same metals (not yet altered). 



J. Dr. Puluj has made the following experiment to prove his 

 suggestion that radiant matter consists of electrode particles 



