April 1, 1895.] 



KNOWLEDGE 



73 



AN ILLUSTRATED 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: APRIL 1, 1895. 



CONTENTS. 



The Circulation of Water in the Atmosphere of IVlars. 



By CiMiLLE Fi,A5r5iAEiox ... ... ... ... ... 73 



With the Second Peary Greeenland Expedition. By 



EiviXD AsTRFP. (lUn.strated) 75 



The Evolution of Fruits. By C F. Marshall, M.D., B.Sc, 



F.E.C.S. {Illustrated) ' 77 



The White- breasted Albatros on Laysan Island. 



(Illustrated) 79 



The Filtration of Water. Bv Samuel Rideal. D.Sc. 



Lond., F.I.C ■ 80 



Winter Life of Insects. Bv E. A. Butler. B.A., B.Pc. 



(Illustrated) ' 83 



Letters: — Arthtte Stbadlin& ; J. Evershed 85 



The Observatories of One Hundred Years Ago. By 



W. T. Ltnn, B..\., F.R.A.S 86 



The Southern IVIilky Way, vjfith the Sydney Star 



Camera. By E.Walter Maunder, F R.A.S. (//^Ms/ra/crf) 87 



Notices of Books 88 



Sussex ; Its Geological Structure. By Prof. J. Logan 



LOBLEY, F.G.S. (Illustrated) ... ' 90 



The House-Spider in Captivity. By the Rev. Henrt 



Nicholson, M.A. (Illustrated) ..." 92 



Some Recent Patents. (Illustrated) 92 



The Magnetic Needle. By YAuaHAN Cornish, M.Sc, 



F.C.S 93 



The Face of the Sky for April. By Herbert 



Sadler, F.R.A.S " ... .. 94 



Chess Column. By C. D. Locock, B.A.Oxon 95 



THE CIRCULATION OF WATER IN THE 

 ATMOSPHERE OF MARS. 



By Camille Flammakion, F.E.A.S., 



Author of " Astronomie Populaire," " Les Etoiles," " I^g 



Terres du Ciel," " La Planete Mars,'' etc. 



THE circulation of water on the earth's surface is 

 necessary for terrestrial life. All living creatures 

 are essentially composed of water — the human 

 body itself contains it in the proportion of 

 seventy per cent. — all require it to live. We have 

 no right, however, to assert that the same law prevails on 

 all the other worlds of the universe ; indeed, the study of 

 nature teaches us to be guarded in our assertions, inasmuch 

 as nature herself shows us that she is infinite in the 

 variety of her productions. Should one world be absolutely 

 destitute of water, this is no sufficient reason for us to 

 declare it to be uninhabited. Do not let us attempt to 

 shut up our ideas in a nutshell. Man, deprived of oxygen, 

 dies, yet, even on our little planet, there are beings to 

 which oxygen is fatal. 



Still, the orbs of any given planetary system have certain 

 affinities of origin, especially when next-door neighbours, 

 like Mars and the earth. On Mars we observe polar snows 

 which are very extensive at the end of every winter, but which 

 by the end of summer have almost entirely disappeared. Is 



this snow formed of water of the same chemical composi- 

 tion as that of our earth ? Possibly, nay probably, it is. 



And what is water? It is an oxide of hydrogen. 

 Now oxygen and hydrogen are diffused through all space, 

 and may be regarded a.s, in some sort, primordial elements.' 

 We may suppose that the combination of those two 

 elements is produced on Mars and Venus in the same 

 manner as on our earth, for all our observations concur in 

 favour of this conclusion. 



But the physical condition of water differs in different 

 worlds, varying according to the temperature, atmospheric 

 pressure and dimensions of the planet, the distribution of 

 its climates, its geological and geographical conditions, its 

 density, &c. Observation leads us to the conclusion that 

 the circulation of water on the surface of Mars is by no 

 means carried out according to the laws that govern its 

 circulation on the surface of our earth. 



Here the mechanism is tolerably simple. Three- 

 quarters of the globe are covered with water, evapoi-ation 

 is considerable, the atmosphere is dense, solar heat 

 perpetually draws off a great quantity of water from the 

 ocean surface, raises it in the form of invisible vapour to a 

 certain height, where it condenses into clouds, and where 

 wmds of considerable power, that owe their force directly to 

 the density of our atmosphere, carry the clouds across conti- 

 nents. Thus transported, aqueous vapours, by dissolving 

 into rain or clouds, give their origin to springs, brooks" 

 streams, and rivers, and bear back to the sea the water that 

 has been raised from it by the action of the sun's rays. 



We may estimate the volume of water thus annually 

 carried off by the atmosphere at 721 trillions (721 x lO'-) 

 of cubic metres— that is to say, about the 4400th part of 

 the total amount of sea water, which is estimated at 3200 

 quadrillions of cubic metres. Supposing the ocean-bed were 

 emptied, it would take forty-four thousand years for all the 

 tidal rivers of the world to fill it again. The solar heat 

 used in effecting this process of evaporation of watery 

 vapour thus raised to the mean height of the clouds would 

 melt eleven thousand millions of cubic metres of iron a 

 year — that is to say, a much more considerable mass than 

 the whole mountain range of the Alps. In the space of a 

 year each square metre of the earth's surface receives 

 2,318,157 of calories— /.c, more than twenty-three 

 thousand millions of calories per French hectare, that is 

 to say, 9,852,200,000.000 kilogrammetres. The sun's 

 heat-radiation exercised on one of our hectares develops 

 over that area, under a thousand varied forms, a power 

 equivalent to the continuous working of 4163 horse-power. 

 Over the whole earth its force is of 510 sextillions of kilo- 

 grammetres, or 217,316,000,000,000 horse-power. 



But very different conditions obtain on the surface of 

 Mars. In the first place, the heat which that planet 

 receives from the sun is less, its distance being 1-52, or 

 about half as much again as that of the earth, and the 

 quantity of heat being 0-43, say less by more than one half 

 than we receive here. But, on the other hand, on Mars 

 the year is nearly as long again as our year, being of 688 or 

 689 days. The heat accumulated on one of its hemispheres 

 during summer would suffice to melt a thick layer of snow, 

 although on the earth, which is nearer to the sun, the six 

 months of the summer season are not sufficient to do so. 

 When the snow begins to melt, a small supply of additional 

 heat^ is often sufficient to complete the dissolving process. 



We must now consider another point of the greatest 

 importance. Our terrestrial atmosphere is very heavy. 

 At the sea level this atmospheric pressure is equivalent to 

 a column of mercury of 0-760 metre. The pressure is of 

 1033 gi-ammes to the square centimetre, or of 103 kilo- 

 grammes to the square decimetre, or 10,830 kilogrammes 



