Einstein does not consider this difference considerable, and regards it as possible to overcome it even in a manner which can be directly pictured. "If the force is exerted by a corpuscular transmission," he explained, "we may imagine a 'force-shadow' into which the bombarding corpuscles cannot penetrate. Thus if an obstacle, which produces such a shadow, becomes interposed between a body A and a body B, then there will be a lesser pressure on the side of B facing A, and hence B will experience a greater corpuscular pressure on the other side, with the result that B will be forced in the direction of A, and the observer would gain the impression of a pull from B to A. Nowadays, when the theory of 'fields of force' dominates our physical views, we need trouble just as little about using corpuscular pressures and impacts as about the vortices which Descartes once considered as the ultimate causes of the motions of the heavenly bodies. The efforts of certain reformers to reintroduce these vortices and whirlpools as explanations must be regarded as futile." "Nevertheless," I answered, "it seems admissible to say that, ultimately, there is always an occult element in every physical explanation, an absolutely final and elementary something which we recognize as a principle, without concealing from ourselves that we have reached the limit of explanation, and our knowledge avails no further. This brings me to another question the discussion of which, as I clearly perceive, leads us on to dangerous ground." EINSTEIN: Don't hesitate to say what is troubling you. I cannot yet see what you are aiming at. M.: I am referring to certain phenomena which are also called "occult"--with the object of discrediting them. They may at times degenerate to hocus-pocus and fall into the category of dubious arts. It seems to me, however, that scientists have not always drawn the line with sufficient care, and that they have been disposed to reject as humbug, without examination, everything inexplicable that dares to present itself in the form of open display. EINSTEIN: In general, they will be in the right, for investigators cannot be expected to occupy themselves with things bolstered up by advertisement, and which are supposed to be connected with some fabulous, occult regions. M.: Nevertheless, in my opinion even among such displays there sometimes occur phenomena which scientists should not pass over with contempt. I, myself, have experienced such cases, and have said to myself: There are stranger happenings here---- EINSTEIN:--than are dreamt of in your philosophy, you were about to say? M.: Exactly. These are things that in the guise of sensationalism often hide a physical truth well worthy of study.