10 



SCIENCE. 



[Vol. II., No. 22. 



deck, and consist of three rooms on as manj' 

 levels : the lowest (32) being a storeroom ; the 

 central one (21) a general laboratorj', or work- 

 room ; and the upper one (9) a deck-labora- 

 tor3' for microscopical work and stiid3'. These 

 rooms communicate with one another bj' means 

 of stairways, but are entirch' cut otf from all 

 the rest of the ship, excepting through the 

 side-doors of the upper laboratorj'. The two 

 lower rooms are protected fore and aft b}' 

 water-tight iron bulkheads, reaching to the 

 main deck ; and the storeroom, which contains 

 the supply of alcohol, can be made a tight 

 box, and instantlj- filled with steam, in case of 

 fire. 



Light is admitted to the upper laborator3^ 

 through a skjiight, and two windows on each 

 side, and to the general laboratory through 

 three ports on each side, and two deck-lights 

 overhead ; but in the storeroom artificial light 

 is uecessarjr. During the daj'-time, therefore, 

 the working-rooms are sufficiently well lighted 

 for all ordinary purposes ; but the sj-stem of 

 electric lamps, which pervades the entire ship, 

 reaches its height of development in these 

 quarters, and every few feet of space contains 

 its little glass globe and horseshoe. The 

 effect at night is very brilliant, and work can 

 then go on about as comfortablj' as in the 

 brightest sunshine. 



[ To be continuecJ,\ 



SURFACE CONDITIONS ON THE OTHER 

 PLANETS. 



In the Popular science monthly for .June appeared 

 an article entitled ' Cost of life,' by John Pratt, 

 upon the habitability of the other planets. To his 

 conclusion that most of the larger planets are prob- 

 ably unsuited for habitation by beings like ourselves, 

 I think few astronomers would take exception; but 

 several of his statements as to their surface condi- 

 tions are apparently at variance with modern obser- 

 vation, and with the results of the application of the 

 principles of mechanics. 



As to the light from the planets, he says, " In the 

 first place, as might have been conjectured even 

 before the revelations of the spectroscope, from their 

 great volume of light as compared with their dis- 

 tances from the sun, all of these great bodies [the 

 four exterior planets] are self-luminous." There is 

 some reason to believe that at certain times portions 

 of the surface of Jupiter do shine by their own light, 

 but it is certainly very faint, as otherwise, when his 

 satellites pass into his shadow, they would still reflect 

 some light to the earth. In point of fact, however, 

 even to the most powerful telescopes, they absolutely 

 disappear. As to the three i-emaining planets, their 

 light is so faint at the best, that any determinations 



as to their self-luminosity are entirely out of the 

 question. The spectroscope shows us nothing what- 

 ever on this subject with regard to any of these 

 bodies. 



We are then told, that " the density of Jupiter being 

 about 1.40, and that of the earth 5.48, it follows that 

 the attraction exerted by Jupiter is roughly 300 times 

 that of the earth. A man wbo weighs 1.50 pounds 

 on the earth, if transported to Jupiter, would shake 

 the ground with a ponderous tread of 45,000 pounds, 

 or 22i tons. His own weight would at once crush 

 him into a mere pulp. A hickory-nut, falling from 

 a bough, would crash through him like a rainie-ball. 

 Again : water would weigh fifteen times as much 

 as quicksilver. A moderate wave would shiver to 

 atoms the strongest ironclad, etc." Applying the 



M 

 ordinary formula, W — jy,, — where M, the mass 



of Jupiter, in terms of the earth, is 313, and D, its 

 diameter, is 11, — we find the weight, W, of an object 

 on the surface of Jupiter, equals ?if, or 2i times what 

 it would weigh here : hence our 150-pound man would 

 weigh just 375 pounds there, and would not be seri- 

 ously inconvenienced by a whole battery of hickory- 

 nuts, provided he wore his hat. With reference 

 to Mars, he writes, that " tlie relative mass of Mars 

 being only about ,;'„ that of the earth [it is ^ approx- 

 imately] . . . our typical man would only weigh 

 about 2/ pounds. . . . An 80-ton locomotive would 

 not propel a train of empty cars. ... A rifle-ball might 

 be caught in the hand without harm." According to 

 the law of gravitation, the ' typical man ' would weigh 

 66 pounds. Supposing the SO-ton locomotive re- 

 duced in weight in the proportion he states, the cars 

 would be so also : therefore, under any such conditions 

 whatever, the 80-ton locomotive would draw precisely 

 as great a quantity of matter there as it would upon 

 the surface of the earth. As to the rifle-ball, its 

 stored energy is proportional to J/F-; that is, it is 

 proportional to its mass, and independent of Its 

 weight. But the mass of a body is the same through- 

 out the universe : therefore experiments in catching 

 rifle-balls in the hand on the surface of Mars would 

 be dangerous. 



Finally, referring to Mars, he says, " Nothing can 

 be more certain than that there is no liquid in Mars, 

 and no life." As seen through the telescope, the 

 poles of Mars appear of a brilliant white color. 

 When one of the poles is turned towards the sun, the 

 size of the white spot diminishes, and, when it is 

 turned away again, it increases. Some astronomers 

 have inuagined these white spots to be snow: in that 

 case, it is difficult to account for the disappearance, 

 unless we suppose that it melts. It therefoi'e seems 

 rather a sti'ong way of expressing it to say that 

 " nothing can be more certain than that there is no 

 liquid in Mars." There are several other points 

 raised by our author which would bear mentioning, 

 one or two on the subject of energy, particularly " a 

 large aspect of the question, which seems to have 

 escaped the attention of thinkers;" but I think the 

 points referred to above will be sufficient for the 

 present occasion. W. H. Pickering. 



