Examples.--Frauenhofer discovers that the solar spectrum is crossed by dark lines. These dark lines could not be explained in his time. Therefore we ought not to believe in them.
Newton discovers that the stars move _as if_ they were governed by an attractive force. This attraction could not be explained in his time. Nor is it explained to-day. Newton himself takes the pains to declare that he does not wish to explain it by an hypothesis. "_Hypotheses non fingo_" ("I do not make hypotheses"). So, after the reasoning of our pseudo-logicians, we ought not to admit universal gravitation. Oxygen combined with hydrogen forms water. How? We don't know. Hence we ought not to admit the fact.
Stones sometimes fall from the sky. The Academy of Sciences of the eighteenth century, not being able to divine where they came from, simply denied the fact, which had been observed for thousands of years. They denied also that fish and toads can fall from the clouds, because it had not then been observed that waterspouts draw them up by suction and transport them from one place to another. A medium places his hand upon a table and seems actually to transmit to it independent life. It is inexplicable, therefore it is false. Yet that is the predominant method of reasoning of a great number of scholars. They are only willing to admit what is known and explained. They declared that locomotives would not be able to move, or, if they did succeed, railways would introduce no change in social relations; that the transatlantic telegraph would never transmit a despatch; that vaccine would not render immune; and at one time they stoutly maintained (this was long ago) that the earth does not revolve. It seems that they even condemned Galileo. _Everything_ has been denied.
Apropos of facts somewhat similar to those we are here studying,--I mean the stigmata of Louise Lateau,--a very famous German scholar, Professor Virchow, closed his report to the Berlin Academy with this dilemma: _Fraud or Miracle_. This conclusion acquired a classic vogue. But it was an error, for it is now known that stigmata are due neither to fraud nor miracle.
Another rather common objection is presented by certain persons apparently scientific. Confounding experience with observation, they imagine that a natural phenomenon, in order to be real, ought to be able to be produced at will, as in a laboratory. After this manner of looking at things, an eclipse of the sun would not be a real thing, nor a stroke of lightning which sets fire to a house, nor an aërolite that falls from the sky. An earthquake, a volcanic eruption, are phenomena of observation, not of experiment. But they none the less exist, often to the great damage of the human race. Now, in the order of facts that we are studying here, we can almost never experiment, but only observe, and this reduces considerably the range of the field of study. And, even when we do experiment, the phenomena are not produced at will: certain elements, several of which we have not yet been able to get hold of, intervene to cross, modify, and thwart them, so that for the most part we can only play the rôle of observers. The difference is analogous to that which separates chemistry from astronomy. In chemistry we experiment: in astronomy we observe. But this does not hinder astronomy from being the most exact of the sciences.