But I must confess that my own experience has not been, on the whole, favourable to that kind of popular science writing. It appears to me that the more thoroughly the writer of such an essay has studied any particular scientific subject, the less able must he be to write a fictitious narrative respecting it. Just as those ignorant of any subject are often the readiest to theorise about it, because least hampered by exact knowledge, so I think that the careful avoidance of any exact study of the details of a scientific subject must greatly facilitate the writing of a fictitious narrative respecting it. But unfortunately a narrative written under such conditions, however interesting to the general reader, can scarcely forward the propagation of scientific knowledge, one of the qualities claimed for fables of the kind. As an instance in point, I may cite Jules Verne's 'Voyage to the Moon,' where (apart, of course, from the inherent and intentional absurdity of the scheme itself), the circumstances which are described are calculated to give entirely erroneous ideas about the laws of motion. Nothing could be more amusing, but at the same time nothing more scientifically absurd, than the story of the dead dog Satellite, which, flung out of the travelling projectile, becomes a veritable satellite, moving always beside the voyagers; for, with whatever velocity the dog had been expelled by them, with that same velocity would he have retreated continually from their projectile abode, whose own attraction on the dog would have had no appreciable effect in checking his departure. Again, the scene when the projectile reaches the neutral point between the earth and moon, so that there is no longer any gravity to keep the travellers on the floor of their travelling car, is well conceived (though, in part, somewhat profane); but in reality the state of things described as occurring there would have prevailed throughout the journey. The travellers would no more be drawn earthwards (as compared with the projectile itself) than we travellers on the earth are drawn sunwards with reference to the earth. The earth's attracting force on the projectile and on the travellers would be equal all through the journey, not solely when the projectile reached the neutral point; and being equal on both, would not draw them together. It may be argued that the attractions were equal before the projectile set out on its journey, and therefore, if the reasoning just given were correct, the travellers ought not to have had any weight keeping them on the floor of the projectile before it started, 'which is absurd.' But the pressure upon the floor of the projectile at rest is caused by the floor being kept from moving; let it be free to obey gravity, and there will no longer be any pressure: and throughout the journey to the moon, the projectile, like the travellers it contains, is obeying the action of gravity. Unfortunately, those who are able to follow the correct reasoning in such matters are not those to whom Jules Verne's account would suggest wrong ideas about matters dynamical; the young learner who is misled by such narratives is neither able to reason out the matter for himself, nor to understand the true reasoning respecting it. He is, therefore, apt to be set quite at sea by stories of the kind, and especially by the specious reasoning introduced to explain the events described. In fine, it would seem that such narratives must be valued for their intrinsic interest, just like other novels or romances, not for the quality sometimes claimed for them of combining instruction with amusement.
X.
ON SOME ASTRONOMICAL PARADOXES.
For many years the late Professor De Morgan contributed to the columns of the 'Athenæum' a series of papers in which he dealt with the strange treatises in which the earth is flattened, the circle squared, the angle divided into three, the cube doubled (the famous problem which the Delphic oracle set astronomers), and the whole of modern astronomy shown to be a delusion and a snare. He treated these works in a quaint fashion: not unkindly, for his was a kindly nature; not even earnestly, though he was thoroughly in earnest; yet in such sort as to rouse the indignation of the unfortunate paradoxists. He was abused roundly for what he said, but much more roundly when he declined further controversy. Paradoxists of the ignorant sort (for it must be remembered that not all are ignorant) are, indeed, well practised in abuse, and have long learned to call mathematicians and astronomers cheats and charlatans. They freely used their vocabulary for the benefit of De Morgan, whom they denounced as a scurrilous scribbler, a defamatory, dishonest, abusive, ungentlemanly, and libellous trickster.
He bore this shower of abuse with exceeding patience and good nature. He had not been wholly unprepared for it, in fact; and, as he had a purpose in dealing with the paradoxists, he was satisfied to continue that quiet analysis of their work which so roused their indignation. He found in them a curious subject of study; and he found an equally curious subject of study in their disciples. The simpler—not to say more foolish—paradoxists, whose wonderful discoveries are merely amazing misapprehensions, were even more interesting to De Morgan than the craftier sort who make a living, or try to make a living, out of their pretended theories. Indeed, these last he treated, as they deserved, with a scathing satire quite different from his humorous and not ungenial comments on the wonderful theories of the honest paradoxists.
There is one special use to which the study of paradox-literature may be applied, which—so far as I know—has not hitherto been much attended to. It may be questioned whether half the strange notions into which paradoxists fall must not be ascribed to the vagueness of too many of our scientific treatises. A half-understood explanation, or a carelessly worded account of some natural phenomenon, leads the paradoxist, whose nature is compounded of conceit and simplicity, to originate a theory of his own on the subject. Once such a theory has been devised, it takes complete possession of the paradoxist's mind. All the facts of which he thenceforward hears, which bear in the least on his favourite craze, appear to give evidence in its favour, even though in reality they are most obviously opposed to it. He learns to look upon himself as an unappreciated Newton, and to see the bitterest malevolence in those who venture to question his preposterous notions. He is fortunate if he do not suffer his theories to withdraw him from his means of earning a livelihood, or if he do not waste his substance in propounding and defending them.
One of the favourite subjects for paradox-forming is the accepted theory of the solar system. Our books on astronomy too often present this theory in such sort that it seems only a successor of Ptolemy's; and the impression is conveyed that, like Ptolemy's, it may be one day superseded by some other theory. This is quite enough for the paradoxist. If a new theory is to replace the one now accepted, why should not he be the new Copernicus? He starts upon the road without a tithe of the knowledge that old Ptolemy possessed, unaware of the difficulties which Ptolemy met and dealt with—free, therefore, because of his perfect ignorance, to form theories at which Ptolemy would have smiled. He has probably heard of the
centrics and eccentrics scribbled o'er
Cycle and epicycle, orb in orb,
which disfigured the theories of the ancients; but he is quite unconscious that every one of those scribblings had a real meaning, each being intended to account for some observed peculiarity of planetary motion, which must be accounted for by any theory which is to claim acceptance. In this happy unconsciousness that there are any peculiarities requiring explanation, knowing nothing of the strange paths which the planets are seen to follow on the heavenly vault,