482 



SCIENTIFIC NEWS. 



[Nov. 9, 1888. 



and from the difference between the polar regions and 

 the rest of the surface, that Mars is not in a state of 

 glaciation. 



It may further be asked whether the system of canals 

 and the great spots are sufficiently variable for this ex- 

 planation. Changes have certainly been observed. In 

 1881-1882 the island Cimmeria was totally separated 

 from the region. Amenthes now communicates with 

 this latter between Ethiops and Lake Triton. Fig. 7 

 shows how M. Perrotin represented these details in 1886. 

 Another change, apparently incontestable, is the enlarge- 

 ment of Lake Triton in 1 888. The same may be said of 

 Thoth. This canal in 1886 (fig. 7) is represented only by 

 a small point prolonging Lake Mceris. 



Still, these changes do not affect the grand network of 

 canals. It is the same with the spots which, in their 

 general configuration, are still what they were in 1659, 

 when Huygens first described them in a characteristic 

 manner. 



However, as Schiaparelli very justly says at the end 

 of his third Memoir, " To seek to found an explanation 

 of these singular phenomena upon the scanty and in- 

 complete data which have hitherto been collected would 

 be rashness unparalleled and reprehensible. Yet we 

 may notice that a tendency to gemination or doubling is 

 manifested also in another manner on the surface of 

 Mars. The division of Lake Ismenius, and that which 

 separates Lake Niliacus from Mare Acidalium, seem to 

 be instances of gemination. In like manner the exist- 

 ence of two bays of the Sinus Sabasus (Dawe's forked 

 bay) and the two Atlantides belong to the same category 

 of phenomena. 



We may add some further details, such as the parallel- 

 ism of the Sea of the Syrens, of the Cimmerian, the 

 Tyrrhenian, and the Adriatic Seas ; that of the Atlantides, 

 of Cimmeria, Hesperia, Ausonia, and the lands of 

 Japhet, Deucalion, and Pyrrha. 



We even find two countries in Mars which seem to be 

 copies one of the other. The Great Syrtis corresponds 

 to the Gulf of Pearls, the Nilosyrtis to the Indus, the 

 Astusapes to the Hydaspes, the Phison to the Jamuna, 

 the Typhonius to the Hydraotes, the Horn of Ammon to 

 the Promontory of the Aromes, CEnotria to the region of 

 Pyrrha, Libya to the land of Deucalion. We may say 

 that Tempe is modelled after Elysium, Styx corresponds 

 to the sea Acidalium, Cerberus to Nilokeras, Eunostos 

 to Nilus, Hyblaeus to Ceraunius, Galaxias to Issedon, 

 Cyclops to Ganges, Antaeus to Hydraotes. 



What should we say if we could be transported to 

 Mars, and on observing the earth through a powerful 

 instrument, could see, instead of a single Europe, two 

 European continents, each exactly of the same form, 

 traversed by rivers so identical that the two continents 

 seemed copies the one of the other ? 



A. M. F. Serly says, " Never was a mystery more 

 profound, an enigma more extraordinary, submitted to 

 the human intellect." 



Professor Holden, in a paper entitled Physical Obsetva- 

 tiovis of Mars, made during the Opposition of 1888 at the 

 Lick Observatory, published in Gould's Astronomical 

 Journal, denies the existence of these double canals, but 

 as it seems impossible that so many skilled observers 

 should have been deceived, we await, with great interest, 

 the observations which will doubtless be made during 

 the favourable opposition of 1890-1892, as they will 

 probably assist in clearing up the mystery attached to 

 these markings. 



THE CONDUCTIVITY OF A 

 VACUUM. 



DR. E. EDLUNG has recently replied in Wiede- 

 man's Annalen to the memoir of Dr. Foeppl on the 

 electro-conductivity of a vacuum. He decidedly con- 

 tests the cogency of Foeppl's experiments. His views 

 are the following : Foeppl surrounded a spiral composed 

 of glass tubes, and containing air highly rarefied, with a 

 spiral of copper wire, through which a powerful electric 

 current was transmitted. With this combination Foeppl 

 was unable to recognise an induction-current in the glass 

 spiral, whence he concluded that the highly rarefied air 

 was not capable of conducting electricity. 



Edlund cannot accept this conclusion. He writes : 

 " It is proved experimentally that the electro-motive 

 force excited in metals by voltaic or magnetic induction 

 does not depend on the nature of the metals. This law 

 holds good also for conductors of the second order ; at 

 least, it has been experimentally proved in the case of 

 solutions of sulphate of zinc. The question now arises 

 whether the same law extends to gaseous bodies — a 

 question which has hitherto received no answer. Elec- 

 trically, gases behave in a quite different manner from 

 conductors of the first and second orders. In such con- 

 ductors the potential difference between two points 

 is proportional to the resistance between these points 

 multiplied by the strength of the current. In gases, 

 on the contrary, this difference is independent of the 

 strength of the current. In metallic and liquid con- 

 ductors the resistance is inversely as the section, 

 but in gases it is equally great, whether the 

 section is larger or smaller. Hence it appears very 

 hazardous to ascribe to the constant of induction for 

 gases, the same value as that for solid bodies, in 

 default of any evidence, whether theoretical or experi- 

 mental. Yet Foeppl's conclusion is based upon such an 

 assumption. 



Moreover, Foeppl calculates the strength of the current 

 according to Ohm's formula, which is not valid for gases. 



In favour of the conductivity of a vacuum, Edlund 

 cites the fact that the strength of a current remains 

 unchanged when the distance of the electrodes is in- 

 creased from 1 to 30 centimetres. Further luminous 

 phenomena can be elicited by influence in highly rarefied 

 air, when the resistance decreases progressively to the 

 utmost rarefication. The negative results obtained by 

 Foeppl are due to the fact that the induction-constant of 

 gases is too minute, as also that the electro-motive 

 force of 5,000 volts which he calculates is non-existent. 



The Twinkling of the Stars. — According to Ciel et 

 Terre, in all parts of the sky the scintillation is strongest 

 in winter and weakest in summer. In every season of 

 the year it is more marked in the north than in 

 other directions. Except in summer, it is stronger in the 

 east than in the south and the west. The mean intensi- 

 ties of scintillation corresponding to the four seasons 

 follow regularly the variations of their mean tempera- 

 tures. 



Deep Sea Fishing. — M. Fol (Comptes Rcndus) has 

 attempted to fish at the depth of 800 metres by sending 

 down nets fitted with tubes charged with phosphorescent 

 sulphide of calcium. Unfortunately, the pressure had 

 broken almost all the tubes, and the experiment has thus 

 miscarried. M. Fol proposes to renew the attempt. 



