indeed, we can see the vibrating ether. It is likewise a certain historical fact that man is descended from apes, etc. The discovery of the fossil ape-man of Java proves conclusively the descent of man from the ape. The existence of space and time is also definitely proved. The historical evolution of the human soul from a long series of higher and lower mammalian souls must be regarded as a scientifically proved fact.
We are now ready to take up Haeckel's metaphysics. We shall first discuss the principles upon which his entire system rests and then consider their application to inorganic nature, organic nature and the psychical world.
In the celebrated address which Du Bois-Reymond delivered in the year 1880, and which was afterwards published as the 'Seven World Biddies,' he proposed seven problems: (1) The essence of matter and energy; (2) the origin of motion; (3) the origin of life; (4) the apparently purposive arrangement of nature; (5) the origin of sensation and consciousness; (6) rational thought and the origin of language; (7) the question of free will. Questions 1, 2 and 5 he regards as impossible of solution or transcendent; 3, 4 and 6 are difficult, but can be solved. On question 7 he is undecided. Haeckel makes short work of these riddles. The problem of matter and energy, the problem of motion and the problem of consciousness are solved, he thinks, by his conception of substance; the problem of life, the teleological problem and the problem of reason by the modern theory of evolution, while the free will problem is no problem at all, but a dogma based on mere illusion.
The conception of substance is therefore Haeckel's fundamental principle. Let us see what it means. There is one underlying  This substance is infinite, indestructible and eternal; it fills the infinite space and is in eternal motion. The matter and energy therefore in the universe are constant. This gives us the laws of the conservation of matter and of energy, which really form one single law, the law of substance, the cosmological ground law, the law of the constancy of the universe, which follows necessarily from the principle of causality. This universal substance reveals to us two different aspects, two fundamental attributes: matter, the infinite extended substance-stuff, and mind (Geist), the all-embracing substance-energy. It is God and nature at the same time; body and mindare two different aspects.
- 'Monismus,' p. 16.
- 'Weltraethsel,' p. 97.
- P. 100. See also pp. 18, 73.
- See 'Weltraethsel,' pp. 243fF.