May .9. 1895] 



NATURE 



37 



British, presented by Mrs. Herbert Morris; four \'ellow-bellie<i 

 l.iiillirix {Liolhrix lii/ms) from China, presented by Mr. .Albert 

 i\t:ttich ; a Black-billed Sheathljill {Chiouis iiivior), captured at 

 sea, a Water Kail (Kalliis ac/iia/itiis), British, presented by Mr. 

 John (iunn ; a Lineolated Parrakeet (Bolborhyiiihus lineolatus) 

 /rom Mexico, presented by Mr. Edward Hawkins ; a Puff 

 Adder ( Vipera arictans) from .South .\frica, ]>rcsented by Mr. 

 J. E. Matcham ; a Lear's Macaw (Ara /tar/) from South 

 America, four White-backed Pigeons (Coliimba kuconota) from 

 the Himalaya-s, a Rock-hopper Penguin (Eiidyptes chrysocome) 

 from New Zealand, deposited ; two .Mpine Choughs (Pyr- 

 rhocorax alpinus), European, ])urchased ; an English Wild Cow 

 {Bos laiirtis, var. ), bom in the Gardens. 



OUR ASTRONOMICAL COLUMN. 



Kki,.\tive Densities of Terrestrial PIj^nets. — Atten- 

 tion is drawn to an interesting relation between the diameters and 

 densities of the terrestrial planets, by E. .S. Wheeler (Siicnce, 

 April 19). The planets are plotted with their diameters in miles 

 jis abscissa;, and their densities (the earth being taken as unity) 

 as ordinates, and it is then seen that the points located in this 

 way lie approximately in a straight line. Such a line passes 

 within the limits of the probable errors of all except \"enus. If 

 this relation should prove to represent a natural law, the mass of 

 a planet or satellite could be determine<l from its diameter. 

 Venus is the only one of the five planets (the moon being in- 

 cluded) that is any more discrepant than might be expected from 

 its probable error ; to make it accordant, either its mass must be 

 increased by one-tenth, or its diameter decreased by one- 

 thirtieth. .\ sufficient increase in the mass of Venus is stated to 

 be all that is necessary to explain the movement of the peri- 

 helion i^oint of the orbit of Mercury ; but some of the irregulari- 

 ties ftf .Mercury may be accounted for by the small mass which it 

 is now supposed to have, namely, one-thirtieth that of the earth. 

 In plotting the planetary curve, the density of Mercury adopted, 

 is that derived by Backlund from a discussion of the movements 

 of Encke's comet. 



TiiK Oriiit oi- Co.met 1893 IV (Brooks).— An investiga- 

 tion of the path of this comet, by Signor Peyra, seems to suggest 

 that it is one of a series travelling in the .same elliptic orbit 

 (Ast. jWii/i. No. 3281). This conclusion is based on the simi- 

 larity of the orbit with those of comets 1864 I and 1822 I, the 

 periods of the comets rendering actual identity impossible. The 

 elements c:)f the orbit are as follows : 



T = 1893 Sept. 19-25954 Berlin M. T. 



_ O I II 



Longitude of perihelion 162 22 19) 



,, ,, node ... 174 55 12 , 1S93 



Inclination ... ... 129 50 14 ) 



Eccentricity ... ... o'9964886 



Log'/ •■■ ' 9-90955' 



Period 3516 years. 



The Si'ectrum oi- .M,\rs. — .A very practical conti;ibution to 

 the recent di.scussion as to the spectroscopic indications of 

 aqueous vapour in the atmosphere of Mars is afforded by the in- 

 vestigations of Mr. Jewell as to the amount of vapour necessary 

 to produce effects which can be observed with instruments of 

 specified ]M)wer. {Astrophysical fourital, .\pril.) Expressing 

 the amount of vapour present in the air of Baltimore by the 

 •depth in inches of a layer of water, the observed monthly mean 

 for January is 073, June 3-25. October 1-56, the maximum oc- 

 curring in June. lie concludes that "unless the amount of 

 water in the atmosphere of Mars is greater than that in the 

 earth's atmos])here in October at Baltimore, it is useless to look 

 for the presence of water vapour in the spectrum of Mars, unless 

 our instrumental means are much superior to any hitherto used 

 for that purpo.se." Since instruments of greater <lis|)ersion are 

 unsuitable, because of the Lack of suflicient light, there seems but 

 little chance of obtaining any very deci-sive direct evidence of the 

 presence of water vapour in Mars. It will be remembered that 

 Dr. Janssen and others satisfied themselves as to the indications 

 of water vapour bands in the spectrum of Mars, whilst Prof. 

 Campbell has more recently failed to detect them. 



The chances of iletecting the presence of oxygen, however, if 

 present, do not seem so hopeless, as the B group is readily seen 

 -ivith small dispersion. 



It is also suggested by .Mr. Jewell that attempts should be 

 made to obser\-e the chlorophyll bands in the spectrum of the 

 green areas of the |)Ianets, since one of the bands is cjuite strong 

 in the vegetation spectrum. 



The Astronomical Society ok France, — During the 

 eight years of its existence, this Society has attained a member- 

 ship of nearly 1000. At the annual meeting held recently, Dr. 

 Janssen was elected president, and M. Camille Flammarion 

 general secretary for the current session. The progress of 

 astronomy in 1894 formed the subject of an address by M. 

 Tisserand, the Director of the Paris Observatory. .Among other 

 matters he referred to the reapjjearance of De Vico's comet 

 (Nature, vol. li. p. 542), which he regarded as further e\-idence 

 of the fact that, at certain epochs, comets are subject to increases 

 of brightness which they are incapable of maintaining, the in- 

 creased activity being ])robably due to internal disturbances, the 

 nature of which are not yet understood. It will be remembered, 

 however, that .Mr. Lockyer explains these fluctuations in brilliancy 

 by collisions with meteor-swarms lying in the track of the 

 comet. Referring to minor planets, .M. Tisserand believed it not 

 improbable that those appearing as bright as 1 2th magnitude stars 

 have an average diameter of about 130 kilometres ; that is, about 

 one-hundredth of the earth's diameter ; at that rate, even a thousand 

 of them would not have a total mass equal to a thousandth part 

 that of the earth, assuming that their mean density is not greater 

 than that of the earth. {Bull. Mens. So(. As/, de France, 

 May. ) 



NO. 1332, VOL. 52] 



THE ROYAL SOCIETY CONVERSAZIONE. 



'X'HE annual Royal Society conversazione, to which gentlemen 

 only are invited, was held in the Society's rooms on 

 Wednesday of last week. 



Many branches of science were represented in the exhibits, 

 either by apparatus or by results of research. .An exhibit that 

 attracted much attention was the electrical furnace as used for 

 the melting of chromium, titanium, platinum, and other metals, 

 with high melting-points, shown by Prof. Roberts-Austen, 

 C.B. The furnace consisted of a fire-clay case lined with 

 magnesia, and contained a magnesia crucible. The carbon poles 

 were horizontal, the arc being deflected by means of a magnet 

 on to the material to be heated. For purposes of exhibition, an 

 image of the molten contents of the furnace was projected, by 

 means of a lens and mirror, on to a screen ; the current em- 

 ployed is usually about 60 or 70 amperes at 100 volts. 



Some very valuable metals of the platinum group w'ere ex- 

 hibited by >Iessrs. Johnson, Matthey, and Co., among them 

 being a platinum nugget, weighing 158 ozs. ; palladium ingot, 

 of 1000 ozs. ; rhodium ingot, 72 ozs. ; osmium, melted and 

 sponge ; ruthenium melted by the electric arc ; and pure iridium 

 rolled sheet. 



A magnet, showing the effects of currents in iron on its 

 magnetisation, was exhibited by Dr. Hopkinson. A large 

 electromagnet had buried in its substance two coils of compara- 

 tively small dimensions, one around the centre of the magnet, 

 the other half-way between the centre and the surface. These 

 coils were connectetl to two gah'anometers. On reversing the 

 current round the magnet it was seen that a ccmsiderable time 

 elapsed before either galvanometer showed any suljsUintial cur- 

 rent, and that the current in the central coil occurred much later 

 than in that at a less depth in the mass of iron. 



Prof. J. \. Fleming showed a synchronising alternating 

 current motor and contact maker, for the delineation of 

 the form of alternating current and electromotive force curves, 

 and a form of resistance of small inductance for use with the 

 apparatus. 



An instrument for analysing primary and secondary volts and 

 amperes simultaneously was exhibited by Prof. \V. M. Hicks. 



.Mr. R. v.. Crompton had on view electrically heated appa- 

 ratus, showing the methoil of applying electricity for heatmg 

 tools and ap]iliances used in trade ; also for domestic ]>urposes. 

 Wires of high resistance comixised of nickel, steel, or other suit- 

 able alloys, were embedded in an insulating enamel, and by it 

 attached to the various articles to be heated. By this means 

 loss of heat was obviated. Connection was made with the circuit 

 by means of .safety connectors, in which the contacts were auto- 

 matically protected. The jierfect flexibilit)' of the system was 

 exemjiliiied in the electric oven, which was heated on all sides 

 top, and bottom, anil the temperature of which could be regulated 



