We have heard it said: Oh! Naples is an exceptional, volcanic district. There may exist there some occult or obscure volcanic agency, which suffices to produce the liquefaction; who can tell what strange results may come from a combination of all the volcanic agencies ever at work in that vicinity?
Is Naples the only volcanic district in the world? Does any other volcanic district present anything like this liquefaction, or calculated to throw light on it? Even in Naples, is there another similar example? And has not this liquefaction continued regularly, even when Vesuvius was quiescent for a long term of years. Previous to December, 1631, the volcano had slumbered in perfect tranquillity for nearly two centuries. A French traveller tells of the flocks of cattle he saw browsing within the very crater itself, then a vast green valley sunk in the plateau forming the top of the mountain. Yet all this while the liquefactions continued as they had done before, and as they have done ever since, in other seasons of quiet, and in seasons of active volcanic eruption.
And then, we ask, what other sign or indication is there giving evidence of this natural influence or law? And what sort of a natural law is that which acts only on one single vial of blood, and has not acted on the thousands of others in the same conditions.
Again, it has been urged, in much the same strain, that our knowledge of the laws of nature is still very imperfect. Many laws are as yet undiscovered. Every year is marked by some advance in our knowledge of them. It by no means follows that
this liquefaction is miraculous, merely because as yet we are unable to assign the precise law or laws of nature which govern it. Perhaps, some time, men will discover them. Then all will be plain. Until then, they tell us, philosophy requires us to note carefully and accurately the facts of the case, and to wait for some explanation or solution of them in the future.
It is always well to take note of the facts, and to make our theories subordinate to those facts. What we find fault with our opponents for, in this question, is that they do precisely the reverse: they fix a theory in their minds, and if the facts of the case do not agree with their theory, why, so much the worse for the facts.
One word on the laws of nature. Although there may be many of which we have now no knowledge, and which we may hereafter discover, still we do know some. These may be supplemented—they cannot be contradicted or reversed by any laws hereafter to be discovered. The legitimate conclusions based on the certain knowledge which we have, are not to be impugned or held doubtful until we discover other laws. We do know, for example, that when a man’s head is severed from his body, he dies. All the known and unknown laws of nature cannot make him live again.
It will not do to base an argument in one paragraph on the invariable uniformity of law and order in nature, and, in the next, to maintain that we are as yet all at sea about these laws.
Among the well-known and uncontested laws of nature by which we may be guided in our argument, are several which have a close connection with the subject before us. We refer to them.
I. We know that solid bodies become liquid by increase of temperature; for each body, there is a certain melting-point. Above that, the solid body becomes liquid; below that, it remains solid, or returns to solidity.