July 8, 1897] 



NA TURE 



OUR ASTRONOMICAL COLUMN. 

 Weinek's Lunar Enlargements.— Selenographers will be 

 glad to hear that Prof. Weinek proposes to publish a Lunar 

 Photographic Atlas, which will contain an accurate and artistic 

 representation of the whole visible surface of the moon. The 

 materials that will form the basis and bulk of this atlas have 

 been mainly derived from the series of negatives of the Lick 

 Observatory, which have been enlarged twenty-four times. The 

 maps will be printed by the phototype process direct from 

 Prof. Weinek's enlarged glass diapositives, and will be con- 

 stantly under his supervision and control during their reproduc- 

 tion by the Art Photographical Institute of Carl Bellmann in 

 Prague. The proposed scale of the atlas will be 4 metres 

 to the diameter of the moon ; there will be in all 200 maps 

 26 X 31 cm., and each sheet will give the selenographical 

 latitude and longitude for the centre of the picture, and also the 

 selenographical longitude of the terminator for the latitude 0°. 

 This will greatly facilitate the arrangement of the sheets 

 according to the relative positions of the lunar objects they 

 portray. The publication of such an atlas as this, which re- 

 quires a great deal of outlay, cannot be undertaken unless a 

 considerable number of subscribers are forthcoming. Prof 

 Weinek appeals in the first instance to all the observatories of 

 the world to become subscribers for the ten issues, each to 

 contain twenty lunar landscapes. There should be no diffi- 

 culty in obtaining a sufficient number of applicants, as such a 

 useful and epoch-making publication in selenography should be 

 in the possession of every observatory. 



Martian Markings. — In the current number oi Knowledge, 

 M. Antoniadi brings together in an interesting summary all the 

 more important observations made from the year 1864 of that 

 well-known marking on the surface of Mars, namely, Syrtis 

 Major. The discussion shows that, on the whole, decided 

 changes have taken place in the form of this marking, and that 

 its expansion has invaded the regions occupied by Mceris Lacus 

 and Lilaga. Two new canals have also been recorded during 

 the last few years in this region. The diagramatic sketch, 

 showing the gradual changes recorded during the last thirty- 

 three years, brings out very clearly the reason of the disappear- 

 ance of the lake as such mentioned above. M. Antoniadi 

 remarks, as regards the displacements of "seas" and "lakes," 

 that " absurd and imaginary as they might seem to the ordinary 

 reader, they are simply familiar occurrences to the areographer. 

 Evidently the surface of Mars has some fixed areographical 

 markings ; but the stability of the lesser details and of the poly- 

 gonians of the canal system is so frail, that at times the changes 

 assume a fantastic, grotesque, and almost ridiculous character." 



of a Kelvin quadrant electrometer. The other copjier plate 

 was connected to one of the pair of quadrants of the electro- 

 meter in such a way that by pulling a silk cord with a hinged 

 platinum wire at its end, this copper plate and this pair of 

 quadrants could be insulated from the sheath of the electro- 

 meter and the rest of the apparatus. On doing so with no flame 

 at the bottom of the funnel, no deflection from metallic zero was 

 observed, even when the other plate was kept at the potential of 

 94 volts by the voltaic battery ; this being the highest we have 



LEAKAGE FROM ELECTRIFIED METAL 

 PLATES AND POINTS PLACED ABOVE 

 AND BELOW UNINSULATED FLAMES} 



§ I. TN § 10 of our paper " On Electrical Properties of Fumes 

 proceeding from Flames and Burning Charcoal," commu- 

 nicated to this Society on April 5, results of observations on the 

 leakage between two parallel metal plates with an initial difference 

 of electric potential of 6-2 volts between them, when the fumes 

 from flames and burnings were allowed to pass between them 

 and round them, were given. The first part (§§ 1-4) of the 

 present short paper gives results of observations on the leakage 

 between two copper plates i centimetre apart, when one of 

 them is kept at a constant high positive or negative potential ; 

 and the other, after being metallically connected with the elec- 

 trometer-sheath, is disconnected, and left to receive electricity 

 through fumes between the two. 



The method of observation (see Fig. i) was as follows. Two 

 copper plates were fixed in a block of paraffin at the top of a 

 round funnel 86 centimetres long and 15-6 centimetres internal 

 diameter. A spirit-lamp or a Bunsen burner, the only two 

 flames used in these experiments, was placed at the bottom 

 of the funnel, 96 centimetres below the two copper plates. 

 One terminal of a voltaic battery was connected to one 

 plate, and the other terminal was connected to the sheath 



1 Paper communicated to the Royal Society, Edinburgh, on July .;, bv 

 Ix)rd kelvm, G.C.V.O., F.R S., and Magnus Maclean, D.Sc. 



as yet tried. When the plate was kept at potentials of 2, 4 . . . 

 10 volts, the deflection from metallic zero in three minutes was 

 observed ; but for higher potentials, merely the times of attaining 

 to 300 scale divisions from metallic zero were observed. 



§ 2. The results obtained are summarised in the following 

 table. In every case for potentials below 90 volts there was 

 greater leakage when the uninsulated plate was connected to the 

 negative terminal of the battery. 



Spirit Flatne. 

 Sensitiveness of electrometer = 607 scale divisions per volt. 

 Hence 300 scale divisions corresponds approximately to 5 volts. 



NO. 1445, 'VOL. 56] 



