"If we heat amber, the diamond, and certain other very dense substances by chafing them, they attract small light bodies, because, in cooling off, they attract the air, which draws these corpuscles along with it." Thus the desire to bring still unexplained material facts under the known physical laws of his day led an observer and thinker so prudent and practical as Galileo to formulate a false proposition. If anybody had said to him that in the attraction exercised by amber there was the germ of a new branch of science and the rudimentary manifestation of an energy (electricity) then unknown, he would have replied that it was useless to "have recourse to the aid of the unknown." But the analogy between the error committed by the great physicist and that which modern scholars commit can be pushed still farther. Galileo was familiar with a form of energy which the natural philosophy of our times investigates simultaneously with electric energy, with which it has close relations confirmed by all recent discoveries. If it had been perceived that the explanation which he gave of the phenomenon of amber had no foundation, he would have been able to give his attention to the analogies which the attraction exercised by amber rubbed over light bodies presents with the attraction exercised by the loadstone upon iron filings. When he had got so far, he would very probably have discarded his first hypothesis and would have admitted that the attractive power of amber is a _magnetic phenomenon_. He would have been deceived, however, for it is an _electric phenomenon_. In the same way might not those persons deceive themselves who, in order to escape at any cost the necessity of the hypothesis of spiritistic entities, should insist with a too persistent predilection upon the animistic hypothesis, even when this would be found insufficient to explain all mediumistic manifestations? Might it not be true that, like electric and magnetic phenomena, which are in close interchangeable connection, and frequently appear to us inseparable, animistic and spiritistic phenomena have a common bond? And let us well note that a single fact, inexplicable by the animistic hypothesis and explicable by the spiritistic hypothesis, would suffice to confer upon the latter that degree of scientific value which up to the present time has been so energetically denied to it, just as the discovery of a secondary phenomenon, that of the polarization of light, sufficed to make Fresnel reject the Newtonian theory of emission and admit that of undulation. Did we obtain, during the course of our ten seances with Eusapia, the one fact which is enough to make the spiritistic hypothesis necessarily take precedence of all others?