■C. B. WAEEING. 71 -(41) 



mote, and for the four outer moons of Saturn, from two 

 and one-quarter of our days to forty. In the system of 

 Uranus, the lunar night continues thirty hours on the 

 satellite nearest the planet, and six and three-quarter 

 days on the one most remote, while Neptune's one satel- 

 lite has a night of nearly seventy-two hours. Nights of 

 such length imply intense cold. No vegetation can exist 

 where every night the temperature falls far below the 

 freezing point of water. We must therefore dismiss all 

 idea of inhabitability for the outward hemisphere of each 

 satellite. As to the other hemisphere, it is of course al- 

 ways turned towards its primary and consequently must 

 receive both day and night a vast volume of heat from 

 the latter. This is in addition to what it receives during 

 its day from the sun. Life would scarcely seem possi- 

 ble in such a world. But, as Proctor justly remarks, it 

 is by no means certain that these moons turn on their 

 axes once in a revolution around their primaries. I quote 

 in substance from his Other Worlds Than Ours : Dawes 

 has observed that the markings seen on the third satellite 

 are variable when transiting Jupiter's disk. Bond has 

 seen this satellite as a well defined black spot on certain 

 occasions, while on others, it has appeared quite bright 

 on the disk of the planet. He once saw this satellite 

 bright as at entered on the disk of Jupiter, and about 

 half an hour later as a dark spot. He quotes from Webb' s 

 Celestial Objects. After speaking of the variable light 

 of the satellites, he says : "The disks themselves do not 

 always appear of the same size or form. Maraldi noticed 

 the former fact in 1707, Herschel ninety years afterward 

 inferred also the latter, and both have since been con- 

 firmed. Beer and Madler, Lassell and Secchi, have some- 

 times seen the disk of the second satellite larger than 

 that of the first ; and Lassell, and Secchi, and his assist- 

 ant, have distinctly seen that of the third satellite irreg- 

 ular and elliptical ; while according to the Roman ob- 

 servers, the ellipse does not always lie the same way." 

 Besides this, the specific gravity of Jupiter's moons va- 

 ries according to Laplace's estimates from one-ninth to 

 four-fifths of the specific gravity of water. Certainly 

 these are most astonishing statements, hard to reconcile 

 with any theory thus far advanced. I venture to sug- 

 gest that they point to a gaseous condition of the satel- 



