At the same time, the value of the co-operation of these gentlemen is not denied, only I desire to point out that the comparison with the tunnel is not quite accurate. What Marx said of economic formulas, is true of logical formulas: "In their analysis neither the microscope nor chemical reagents are of any service. The power of abstraction must replace them both." The two sciences will finally meet, not because each one of them digs away in its own one-sided fashion, but because the miners meet after working hours and exchange their experiences. And the philosophers may be the dominant party, because they are specialists in logic and therefore prepared to utilize anything which may serve their purpose, no matter from what side it comes. The other party, on the other hand, has its own specialties and promotes the cause of logic in a secondary and involuntary fashion. Natural science has its own monism which is distinguished from philosophical proletarian monism in that it does not appreciate the historical outcome of philosophical research. One of the most prominent representatives of the former is Noire. He entitles one of his little works "Monistic Thought," but shows himself on its pages as a very unclear dualist. He speaks of the "dual nature of causality" and relates that the mind operates with a different causality than the mere mechanical one. He calls this other "sensory causality." According to him the world has only two attributes: "Motion and sensation are the only true and objective qualities of the world.... Motion is the truly objective ... though it is admitted that it gives us only the phenomenon.... Sensation makes up the internal nature of things. Every subject, whether man or atom, is endowed with the two qualities of all beings, viz., motion and sensation." Thereupon I have carefully looked for an explanation in Noire's works, why he regards the nature of things as composed of an external and an internal quality, and why sensation should not be regarded as a sort of motion, but the only reason I could find was the dualistic nature of his "monistic" reasoning. As Schopenhauer provided the whole world with a "will," so Noire provides it with "sensation."