Nov. II, iS8o] 



NATURE 



43 



and third. One '"of them, which lasted ten seconds, was so 

 powerful that not a single house remained uninjured. A general 

 panic reigns in the town. Many of the inliabitant, including 

 the Cardinal- Archbishop, have taken to flight. It is impossible 

 to estimate the whole txtent of the damage. The number of 

 persons injured is at present estimated at thirty. 



The eruption of Vesuvius continues to increase in activity. 

 Two large streams of lava are at present (November S) flowing 

 from the crater to the base of the cone. 



In Trof. Huxley's article on the Challcnget- Publicitions last 

 week, line ii from top of p. 2, col. 2, should read "direct and 

 but little modified descendants," instead of "dried" &c. 



OUR ASTRONOMICAL COLUMN 

 Hartwig's Comet (iSSo d). — In a circular issued by Prof. 

 Winnecke from the Observatory of Strasburg on the 1st inst., 

 he gives reasons fur assuming that the comet detected by Dr. 

 Hartwig on September 29 may have a much shoner period than 

 was conjectured in his first circular. On calculating parabolic 

 elements from the Strasburg observations of September 29 and 

 Octobers, and one by Prof. Auvvers at Berlin on October 17, 

 MM. Ambronn and Wislicenus, students in the University of 

 Strasburg, found the middle observation could not be more 

 closely represented than with an error of something over two 

 minutes of arc. Prof. Winnecke, as was stated in our previous 

 notice, considered he had reason for suspecting the identity of 

 Hartwig's comet with that of 1506, and a further examination 

 of the historical descriptions has led him to direct attention to 

 the comets of 13S2, 1444, and 1569, and with the perihelion 

 passage fixed to July 13, 1444, and October 15, 1569, he finds 

 geocentric positions which he regards as in sufiicient agreement 

 with the records. A period of revolution of about 62I years is 

 therefore obtained, and an ellipse with this period has been 

 adapted by Dr. Schur and Dr. Hartwig to the observations on 

 September 29 and October 14 and 24. The resulting elements 

 are as follow : — 

 Perihelion Passage, iSSo, September 6'5S949 M.T. at Berlin. 



Longitude of perihelion 



,, ascending node 



Inclination 



Log. excentricity 



Log. semi-axis major 



Log. mean diurnal motion ... 



M. Eq. iSSo-o. 



83 33 2S 



44 33 30 



3S S 56 



9'990iibO 



t 196457 



1755321 



The error of the place deduced from this ellipse on October 

 14 is + 28' in longitude and the same in latitude, and it is 

 remarked that the error in longitude does not admit of being 

 destroyed without an increase of error in latitude. Thi^-, how- 

 ever. Prof. Winnecke suggests, may arise from the assumed 

 period of 62i years being really a multiple of the true one. 

 The comet approaches near to the orbit of Mercury at the 

 .ascending node, though at the present time not sufficiently close 

 to occasion any change in the character of the orbit. Still at 

 some past epoch the effect of perturbation may have brought 

 the orbits into coincidence or nearly so, and Prof. Winnecke 

 hints that the planet Mercury might have been the means of 

 impressing an elliptical form on the comet's orbit. 



it is clearly a case in which those observers who are in the 

 possession of very powerful instruments may render most material 

 service towards deciding whether we have to do with a comet of 

 comparatively short period. If it is practicable to secure good 

 observations for position after the next period of moonlight, it 

 may then be possible to obtain evidence pro or con, by direct 

 computation of the orbit, though unfortunately observations did 

 not commence until the comet had reached the extremity of the 

 parameter, or in other words had attained an angular distance of 

 90° past the perihelion point. 



Discovery of a Comet. — Lord Lindsay notifies the discovery 

 of a comet at his observatory, Dunecht, during the night of the 

 7th inst., by Mr. Luhse in the constellation Lacerta ; the position 

 at ish. 30m. in R.A. 22h. 45m. 54s., Dechnation 42° 33' 7 ; 

 daily motion in R.A. + 6ni. 58s., in Dec!. + 1° 8'. This is far 

 from any position which the expected comet of 1S12 could occupy 

 on the above date. 



Cekaski's Variable Star. — Mr. Knott obtained a very 

 complete observation of the descending and ascending lifhtcurve 



of this newly-detected variable on November 2 ; the minimum 

 appears to have occurred about I ih. G. M.T. The period will 

 be somewhat less than 2i days. 



PHYSICAL NOTES 



Prof. Lorei,'Z has given in Wicd. Ann., No. 9, a develop- 

 ment of his theory of "refraction-constants" (published before 

 in I lanish), and described experiments bearing on it. The 

 problem contemplated was to find that function of the re- 

 fractive index, freed from dispersion, and of the density of a 

 body, which is constant with varying density of the body, 

 supposing the molecules themselves unchanged. It is assumed 

 that bodies consist of molecules in whose intervals light is 

 propagated with the same velocity as in vacuous space ; further, 

 that the bodies are isotropic, and their molecules of spherical 

 form. Herr Lorenz arrives at a simple expression for the re- 

 fraction-constant, the constancy of \\hich, as also the correctness 

 of the assumption as to light moving with the same velocity in 

 the intervals of molecules as in vacuo, had to be proved. He 

 determined the refraction constants of several bodies in the 

 liquid and the vaporous states, viz., ethylic ether, ethylic alcohol, 

 water, chloroform, ethylic iodide, ethylic acetate, and sulphide 

 of carbon. The refraction was determined with sodium and 

 lithium light, and at temperatures of 10°, 20°, and 100°. He 

 found that in passage of the substances from the liquid to the 

 vaporous state the refraction-constant varies very little (only 

 about 5 per cent, at most). Dispersion also showed great 

 constancy. Another Danish physicist, K. Prytz, has extended 

 the inquiry to some ten other substances (loc. cit.), and confirmed 

 the assumption of refraction constants. 



With regard to electricity, Herr Hoorweg ( IViid. Ami., No. 9) 

 divides all bodies into two groups, (a) those in w hich the conduc- 

 tivity rises with the temperature (dielectrics), and (b) those in 

 which it decreases with rise of temperature (adielectrics). He 

 endeavours to prove by experiment (i) that both dielectric bodies 

 with adieleclric, and adelectric with each other, yield contact 

 electricity ; (2) that this electricity has .always the same sign as 

 that which arises with gentle friction or pressure. (The some- 

 times different action of strong friction is ascribed to the influence 

 of the raising of temperature.) Not only does electricity arise 

 through the different heat-motion at the places of contact of two 

 heterogeneous substances, but this cause is fully sufficient to 

 explain all development of electricity. 



Herr Narr has lately obtained some interesting results in 

 experimenting further on the behaviour of electricity in gases, 

 and especially in vacuo (H'icd. Ann., No. 9). In the middle of 

 a hollow brass sphere on a glass support was suspended a metallic 

 ball by means of a platinum wire passing (insulated) through a 

 metallic stopper to an electrometer. Vacua could be produced 

 in the sphere. A charge of electricity imparted to the con- 

 ducting system underwent the same process of dispersion in 

 Tacuo as where the space was full of gas. The outer surface of the 

 hollow sphere, one minute and also one hour after the charging, 

 had the same electricity as the conducting system. Herr Narr 

 further finds that the process of dispersion in gas-filled space is 

 not perceptibly influenced by the hollow sphere being insulated 

 or being connected to earth, if the original charging be done while 

 the sphere is connected to earth ; the dispersion constant diminishes 

 in both cases, at least at the beginning. But if the conducting 

 system be charged while the hollow sphere is insulated, the latter 

 has in this state one minute, and likewise one hour to one hour 

 and a half after, electricity of the same sign with the conducting 

 system, and the first connection of the hollow sphere to earth 

 occasions a temporary outflow. Herr Narr shows reasons for 

 believing that the electricity on the hollow sphere finds its way 

 through the gas space. 



A NEW series of experiments of extended range, by Herr Roth, 

 on the compressibility of gases, is described in li'icd. Ann., 

 No. 9. The relations between pressure, volume, and tempera- 

 ture, in the case of carbonic acid, sulphuric acid, ammonia, and 

 ethylene, are studied. The results are mainly confirmatory of 

 van dtr Waal's formula. 



A NEW balance designed to be easily transportable, light, and 

 yet stable, w ithout fixing to the table, and to serve in inspection 

 of widely various weights (by Government officials in Hungary), 

 ■was lately brought before the Buda-Pesth Academy by Herr von 

 Krasper (see Wied. Beibl. No. 9, p. 63S). Among other features, 



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