[Footnote 7: _The Law of the Conservation of Substance_. Strictly taken, this belongs also to "scientific articles of faith," and could stand as the first article of our "monistic religion." Physicists of the present day, it is true, generally (and correctly) regard their "law of the conservation of energy" as the immovable foundation of all their science (Robert Mayer, Helmholtz), just as in like manner chemists so regard their fundamental law of the "conservation of matter" (Lavoisier). Sceptical philosophers could, however, raise certain objections to either of these fundamental laws with as much success as against their combination into the single superior law of the "conservation of substance." As a matter of fact, dualistic philosophy still attempts to raise such objections, often under the guise of cautious criticism. The sceptical (in part also purely dogmatic) objections have a semblance of justification only in so far as they relate to the fundamental problem of substance, the primary question as to the connection between matter and energy. While freely recognising the presence of this real "boundary of natural knowledge," we can yet, within this boundary, apply quite universally the "mechanical law of causality." The complicated "phenomena of mind," as they are called (more especially consciousness), fall under the "law of the conservation of substance" just as strictly as do the simpler mechanical processes of nature dealt with in inorganic physics and chemistry. Compare note 16.]