434 



SCIENTIFIC NEWS. 



[Oct. 26, 1 J 



described. Alongside one of the old canals, or at least 

 of one of the canals as they had been previously seen, 

 there appeared a new one (i.e., one not seen before), in 

 most cases strictly parallel to the former, and terminating 

 not at the same points, as if the old canal had been 

 merely resolved into two components by the use of a 

 more powerful instrument, but leading to neighbour- 

 ing points, as if a new canal had been dug 

 parallel to the former. The totality of these parallel 

 or twin lines, intersecting each other too in all 

 directions, seemed like an inextricable net. A super- 

 ficial examination might lead to the conclusion that 

 the original state of the surface of Mars had been entirely 

 overturned. Such, however, is not the case ; the old 

 lines can be exactly identified, though each is accompanied 

 by a new line. Hence the new map is something like 

 what the old one would look if viewed through the 

 medium of a doubly- refracting crystal, such as Iceland spar. 



The discoveries of Schiaparelli had been made with 

 the excellent 8-inch equatorial by Merz, in the possession 

 of the Milan Observatory. But more powerful means 

 were soon placed at his disposal, and in 1886, when 

 Mars was again in opposition, he was able to examine 

 the planet with an 18-inch telescope by the same maker 

 and of the same excellent construction. 



In the same season M. Perrotin, of the Nice Obser- 

 vatory, examined Mars with the 38-centimetre ( = 7§--in.) 

 equatorial. After several attempts he succeeded in 

 detecting the gemination of many of the mysterious lines, 

 and his observations were checked over by M.M. Thollon, 

 Gautier, and Trepied. Thus was obtained a full con- 

 firmation of the beautiful discoveries of Schiaparelli on 

 the singular physical constitution of Mars. 

 (To be continued) 



LUMINOUS OR SILVERY CLOUDS. 



ACCORDING to the opinion of Professor W. Kohl- 

 - rausch, the luminous phenomena in the sky from 

 November, 1883, to the summer of 1884, during which 

 time splendidly illuminated clouds appeared with great 

 frequency, were produced by volcanic eruptions, al- 

 though it may also be assumed that the matter of these 

 luminous clouds came from the regions of space. O. 

 Jesse (Meteorologische Zeitschrift, v.- p. 90) considers the 

 former view the more probable ; and, without professing 

 to give a final decision on the whole question, he endea- 

 vours to explain the striking fact that between the first 

 appearance of the intense purple light and the first 

 occurrence of the luminous clouds an interval of eighteen 

 months could elapse. 



According to Jesse, the luminous clouds consist of a 

 number of minute crystals formed from certain very 

 light gases of unknown nature under the influence of the 

 low temperature of the upper regions of the atmosphere. 



As Verbeck assumes, the mass hurled up from Kraka- 

 toa, which, on May 20th, 1883, reached a height of more 

 than six miles, attained on August 26th-27th an altitude 

 of from ten to twelve miles, a calculation which agrees 

 fairly with the results of O. Jesse, who determines the 

 height of the luminous stratum of vapour at about eleven 

 miles. Without question the matter ejected from the 

 volcano consisted of solid particles of dust, and also of 

 gases. The latter, with the exception of the condensed 

 watery vapour, were diffused in the air. These gases, 

 in consequence of their rapid ascent, were diffused not in 

 the lower but in the upper regions of the air, and were 



then lost in space, if we admit that there is no hard and 

 fast boundary between space and our atmosphere. Such 

 a gas, whose point of condensation was not too low, 

 might in consequence of this ascent arrive in regions of 

 such a temperature that it would become liquified. By 

 the rapid evaporation of the liquid thus formed we have 

 a further reduction of temperature and a consequent 

 formation of crystals. In the strata where this crystal- 

 lisation takes place, the atmospheric air will be freed 

 from the foreign gases, so that further quantities of the 

 same may make their way upwards from the lower 

 strata. It is plain that the gas in question may even be 

 heavier than atmospheric air, but in consequence of the 

 mutual interpenetration of gases it may still arrive at very 

 great altitudes, though more time must elapse before th.2 

 stage of crystallisation is reached. 



After the congelation the crystals fall down into lower 

 and consequently warmer regions of the air until again 

 an evaporation and an ascent takes place. These circum- 

 stances may be sufficient to explain the extremely rapid 

 changes of form of the luminous clouds. 



More difficult is the explanation in what manner the 

 scattered crystals arrange themselves in large masses so 

 as to form a luminous cloud by the coalescence of minute 

 corpuscles. Here then come into play processes similar 

 to those, in consequence of which thinly-scattered particles 

 of vapour are agglomerated to form sharply defined 

 thunder-clouds. For the coalescence of the widely 

 diffused crystals a considerable time must be required, 

 and we may thus understand the long interval between 

 the eruption of Krakatoa and the first appearance of the 

 luminous clouds. 



Jesse seeks to explain, further, the periodic appearance 

 by the luminous clouds. Encke had formerly explained 

 the prolonged revolution of the comet bearing his name 

 by the supposition that space contains a resisting medium. 

 William Siemens, in order to account for the constant 

 renewal of solar energy, makes use of the hypothesis that 

 the general space of our solar system is filled with gases 

 which must be regarded as a continuation of the atmos- 

 phere of the sun and the planets. At the same time we 

 may assume that the air of the interplanetary space lags 

 behind the planets in their revolutions round the sun. 

 Every planet will then experience a continual, but slow 

 and partial, renewal of its atmosphere. In this manner the 

 hemisphere which is turned towards the direction in 

 which the earth is moving undergoes a constant afflux of 

 matter from the regions of space, whilst from the opposite 

 hemisphere there takes place a constant efflux. In the 

 atmospheric strata, at from six to about sixty miles above 

 the earth's surface, there may be a slight current in the 

 direction opposite to her motion which carries along the 

 minute solid particles suspended in the air. It would, 

 therefore, be probable that the luminous clouds which 

 since 1885 have been regularly seen in the months of 

 June and July will be visible for half a year in the south 

 temperate zone. It deserves notice that at the time of 

 the Krakatoa eruption the north pole was turned towards 

 the direction of motion of the earth, whence, in accordance 

 with the above suppositions, the vapours of the eruption 

 would extend more to the south than the north. 



The above hypothesis does not explain the fact that 

 since their first appearance the luminous clouds have con- 

 siderably decreased. It is possible that the gas has entered 

 into combinations which no longer admit of its ascent, or 

 that the crystals formed in the upper regions of the air 

 have been carried away by the above-mentioned current. 



