1874.) The Saturnian System. 17 
from the vapourous to the liquid condition. I do not say 
that this is the actual state of matters; on the contrary, I 
shall endeavour to show that the real condition of the 
Saturnian and Jovian atmospheres is altogether different. 
But this is the conclusion to which we are led if we assume 
that these atmospheres have such a depth as telescopic 
observation indicates, and exist at ordinary temperatures. 
But if we assume, as we must on the assumption of ordi- 
nary temperature, that, at a comparatively moderate depth 
below the apparent limits of the globes of Saturn and 
Jupiter, the liquid condition is attained by mere vastness of 
atmospheric pressure, or else exists simply because the 
atmosphere is not so deep as we have been supposing, we 
have, in the small mean densities of Jupiter and Saturn, a 
problem of no ordinary difficulty... We cannot possibly 
believe (in the presence of the results experimentally shown 
to follow from applying great pressure to solid materials) 
that there can be cavernous openings in the interior of 
these vast globes. Under enormous pressure, solids, even 
such solids as iron, gold, and platinum, are perfectly plastic. 
They vun like fluids. And no pressure ever yet applied 
experimentally is for a moment comparable with the pressure 
which must exist at very moderate depths below the surface 
of Jupiter and Saturn. It is as incredible that cavernous 
openings or great hollow interiors exist in the solid globes of 
Saturn and Jupiter as it would be that cavernous openings 
should exist in the depths of ocean, and with no other walls 
but the water itself. If the globes of Saturn and Jupiter 
are in the main solid or liquid, they are solid or liquid 
throughout, without gaps or interstices. Moreover, they are 
subject to a pressure constantly increasing from surface to 
centre, and enormously greater than that at the earth’s 
centre, at but a relatively short distance from the surface. 
In Jupiter especially, the pressure must increase with great 
rapidity, on account of the greatness of his attractive power; 
for gravity at his surface exceeds gravity at the earth’s 
surface fully 2} times. And again, in Jupiter’s enormous 
globe, a depth such as that which separates the centre of 
the earth from her surface is relatively insignificant, being 
less than a tenth part of the distance separating his centre 
from his surface, on our present assumptions. ‘That a solid 
or liquid globe, subjected to such enormous pressures 
throughout by far the greater part of its volume, should 
have a mean density less than a fourth of the earth’s, as in 
Jupiter’s case, or less than a seventh of the earth’s, as in 
Saturn’s, must assuredly be regarded as a most surprising 
VOL. IV. (N.S.) D 
