318

THE PLANET JUPITER.

heat to make it an agreeable place of residence during a longperiod of further gradual cooling, until at last, instead of beingtoo hot, it will become too cold for habitation.

As its habitability at the present time seems to be soimprobable, we need hardly devote much space to discuss theseasons of Jupiter ’s year, or the climatic conditions existingupon it. We will only remark in passing, that, its axis beingnearly perpendicular to the plane of its orbit, its polar regionsonly extend for about 3° around each pole, instead of for 23-1°,as upon the Earth . Upon nearly the whole surface a residentwould therefore find Spring, Summer, Autumn, and Winter tobe almost alike ; in fact, a sort of never-ending Spring wouldreign in every latitude, the Sun rising to nearly the samemeridian altitude each day in the year; that altitude, however,being less the farther any locality might be from the equator.

The actual intensity of the Sun ’s heat and light upon Jupiter would be about J-th of that which is enjoyed by the Earth .The Sun ’s disc would appear to be of a diameter less than ith,and of an area equal to about Wth, of that which it exhibits tous; and it would seem (owing to the rapid axial rotation of theplanet) to move across the sky 2| times as quickly as it doesto an observer upon the Earth , so that it would pass over thewidth of its own diameter in about every successive 9 secondsof our time.

We may also remark that, if there should be any inhabitantsupon such a planet, they would, of course, have to be muchsmaller than upon the Earth , the attraction of gravity upon itssurface being, as we have shown in page 296, about 2.) timesas great. This is in accordance, although in a reversed direc-tion, with the reasoning by which we showed, in our previousstatements with regard to the satellites of Mars and the MinorPlanets, that, the smaller the attraction of gravity upon anysurface, the larger should be the scale of any beings upon it.In like manner, the greater the attraction of gravity the smallermust they be, in order to prevent their own weight from de-stroying them. There is, therefore, an important and funda-mental error of principle in a somewhat amusing quotationin the first volume of Admiral Smyth ’s “ Celestial Cycle,”