But this difference in the accessibility of phenomena is not due to their peculiar nature. It is connected with a different fact, with the modes of excitement which call them forth. If the visual sensation is common to all, it is because the exciting cause of the sensation is an object external to our nervous systems, and acting at a distance on all.[34] The tactile sensation is at the beginning more personal to the one who experiences it, since it requires contact; and the lower sensations are in this intimacy still in progress. And then, the same object can give rise, in common-place circumstances, to a sensation either common to all beings or special to one alone. The capsule of antipyrine which I swallow is, before my doing so, visible to all eyes; once in my mouth, I am the only one to perceive it. It is therefore possible that the same sensation, according to the displacements of the object which excites it, may make part of the internal or of the external series; and as all psychic life is sensation, even effort, and, as we are assured, emotion, it follows that our argument extends to all the psychical elements. Finally, the internal or external character of events, which might be called their geographical position, is a characteristic which has no influence upon the method destined to take cognisance of it. The method remains one. Introspection does not represent a source of cognition distinct from externospection, for the same faculties of the mind--reason, attention, and reflection--act on sensation, the source of the so-called external sciences, and on the idea, the source of the so-called inner science. A fact can be studied by essentially the same process, whether regarded by the eyes or depicted by the memory. The consciousness changes its object and orientation, not its nature. It is as if, with the same opera-glass, we looked in turn at the wall of the room and through the window. I can even quote on this point a significant fact: there are observers who are organised in such a way that they especially observe by memory. Placed before the sensorial phenomenon which strikes their senses, they are sometimes amazed, as if hypnotised; they require to get away from it to regain consciousness of themselves, to analyse the fact, and to master it, and it is by means of the memory that they study it, on condition, of course, of afterwards coming back to verify their conclusions by a fresh observation from nature. Will it be said that the physicist, the chemist, or the biologist who follows this slow method, and who thus observes retroactively, practises physics and biology by introspection? Evidently this would be ridiculous.