154 COSMIC FIIILOSOFHi: [pt. t 



and will continue to do so while the sun's attraction, and the 

 force with which the earth tends to advance in a direct line 

 through space, continue to coexist in the same quantities as 

 at present. But vary either of these causes, and the unvary- 

 ing succession of motions would cease to take place. The 

 series of the earth's motions, therefore, though a case of 

 sequence invariable within the limits of human experience, 

 is not a case of causation. It is not unconditional." l July 

 does not cause August, though it invariably precedes it. For 

 the sequence is conditioned by the coexistence of a given 

 ratio bei *veen the solar gravitation and the earth's tangential 

 momentum, with a given inclination of the earth's axis of 

 rotation to the plane of its orbit. Vary either of these 

 factors, which are the real causes of the seasons, and the 

 hitherto invariable sequence between July and August will 

 be altered. 



Causation may therefore be defined as the unconditional 

 invariable sequence of one event, or con unence of events, 

 upon another ; and this is all that is given in the pheno- 

 menon. But metaphysics is not content with this conception 

 of Cause. It prefers to regard causation as a kind of con- 

 straint by which the antecedent event obliges the consequent 

 event to follow it. It postulates a hidden power, an occulta 

 vis, in the cause, which operates as an invincible nexus 

 between it and the effect. And it is by virtue of the exer- 

 tion of this occult energy that cause, as formulated by meta- 

 physics, is called Efficient Cause, in distinction from the only 

 cause known to science, — the unconditional invariable ante- 

 cedent, which may be termed Phenomenal Cause. 



This explanation bears the distinctive marks of a meta- 

 physical hypothesis, as enumerated in the preceding chapter. 

 To the elements of sequence, invariableness and uncondi- 

 tioaalness embraced in the scientific explanation, it superadds 

 an occulta vis, an element which is not given in the pheno- 

 * Mill, System of Logic, 6th edit. vol. i. pp. 379-381. 



