NEWS FROM JUPITER. 
353 
portion of Jupiter’s interior, we know quite certainly that there 
must be enormous pressure throughout the whole of the planet’s 
globe, and that even a vaporous nucleus would be of great 
density. For it is to be remembered that all that I have said 
above respecting the possibility of gases existing at great 
pressures applies only to ordinary temperatures — such tem- 
peratures, for example, as living creatures can endure. At 
exceedingly high temperatures much greater pressure, and 
therefore much gi'eater density, can be attained without lique- 
faction or solidification. And in considering the effect of 
pressure on the materials of a solid globe, we must not fall into 
the mistake of supposing that the strength of such solid ma- 
terials can protect the material from compression and its effects. 
We must extend our conceptions beyond what is familiar to 
us. We know that any ordinary mass of some strong, heavy 
solid — as iron, copper, or gold — is not affected by its own weight 
so as to change in structure to an appreciable extent. The 
substance of a mass of iron forty or fifty feet high, would be 
the same in structure at the bottom as at the top of the mass ; 
for the strength of the metal would resist any change which 
the weight of the mass would (otherwise) tend to produce. But 
if there were a cubical mountain of iron twenty miles high, 
the lower part would be absolutely plastic under the pressure 
to which it would be subjected. It would behave in all respects 
as a fluid, insomuch that if (for convenience of illustration) we 
suppose it enclosed within walls made of some imaginary (and 
impossible) substance which would yield to no pressure, then, 
if a portion of the wall were removed near the base of the 
iron mountain, the iron would flow out like water * from a hole 
near the bottom of a cask. The iron would continue to run 
out in this way, until the mass was reduced several miles in 
height. In Jupiter’s case a mountain of iron of much less 
height would be similarly plastic in its lower parts, simply 
because of the much greater attractive power of Jupiter’s mass. 
Thus we see that the conception of a hollow interior, or of any 
hollow spaces throughout the planet’s globe, is altogether in- 
consistent with what is known of the constitution of even the 
strongest materials. 
How, then, are we to explain the relatively small mean density 
of Jupiter’s globe? On the supposition that his atmosphere is 
less than fourteen miles deep, we cannot do so ; for there is 
nothing hypothetical in the above considerations respecting a 
solid globe as large as Jupiter’s, excepting always the assump- 
* The effect of pressure In rendering iron and other metals plastic has 
been experimentally determined. Cast steel has been made to flow almost 
like water, under pressure. 
VOL. XII. — NO. XLIX. 
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