It would be easy to point out a great number of other unexplained anomalies. Physicists assert, as an absolutely universal law, that in liquefaction heat is absorbed;19 yet sulphur is at least an apparent exception. The two substances, sulphur and selenium, are, in fact, very anomalous in their relations to heat. Sulphur may be said to have two melting points, for, though liquid like water at 120° C., it becomes quite thick and tenacious between 221° and 249°, and melts again at a higher temperature. Both sulphur and selenium may be thrown into several curious states, which chemists conveniently dispose of by calling them allotropic, a term freely used when they are puzzled to know what has happened. The chemical and physical history of iron, again, is full of anomalies; not only does it undergo inexplicable changes of hardness and texture in its alloys with carbon and other elements, but it is almost the only substance which conveys sound with greater velocity at a higher than at a lower temperature, the velocity increasing from 20° to 100° C., and then decreasing. Silver also is anomalous in regard to sound. These are instances of inexplicable exceptions, the bearing of which must be ascertained in the future progress of science.
When the discovery of new and peculiar phenomena conflicting with our theories of the constitution of nature is reported to us, it becomes no easy task to steer a philosophically correct course between credulity and scepticism. We are not to assume, on the one hand, that there is any limit to the wonders which nature can present to us. Nothing except the contradictory is really impossible, and many things which we now regard as common-place were considered as little short of the miraculous when first perceived. The electric telegraph was a visionary dream among mediæval physicists;20 it has hardly yet ceased to excite our wonder; to our descendants centuries hence it will probably appear inferior in ingenuity to some inventions which they will possess. Now every strange phenomenon may be a secret spring which, if rightly touched, will open the door to new chambers in the palace of nature. To refuse to believe in the occurrence of anything strange would be to neglect the most precious chances of discovery. We may say with Hooke, that “the believing strange things possible may perhaps be an occasion of taking notice of such things as another would pass by without regard as useless.” We are not, therefore, to shut our ears even to such apparently absurd stories as those concerning second-sight, clairvoyance, animal magnetism, ode force, table-turning, or any of the popular delusions which from time to time are current. The facts recorded concerning these matters are facts in some sense or other, and they demand explanation, either as new natural phenomena, or as the results of credulity and imposture. Most of the supposed phenomena referred to have been, or by careful investigation would doubtless be, referred to the latter head, and the absence of scientific ability in many of those who describe them is sufficient to cast a doubt upon their value.
It is to be remembered that according to the principle of the inverse method of probability, the probability of any hypothetical explanation is affected by the probability of each other possible explanation. If no other reasonable explanation could be suggested, we should be forced to look upon spiritualist manifestations as indicating mysterious causes. But as soon as it is shown that fraud has been committed in several important cases, and that in other cases persons in a credulous and excited state of mind have deceived themselves, the probability becomes very considerable that similar explanations may apply to most like manifestations. The performances of conjurors sufficiently prove that it requires no very great skill to perform tricks the modus operandi of which shall entirely escape the notice of spectators. It is on these grounds of probability that we should reject the so-called spiritualist stories, and not simply because they are strange.