these hypotheses, Lavoisier hermetically sealed some tin in a glass retort, and weighed the whole.  He then heated it; and, when the tin was calcined, weighed the whole again, and found it the same as before.  No substance, therefore, either light or heavy, had escaped.  Further, when the retort was cooled and opened, the air rushed in, showing that some of the air formerly within had disappeared or lost its elasticity.  On weighing the whole again, its weight was now found to have increased by ten grains; so that ten grains of air had entered when it was opened.  The calcined tin was then weighed separately, and proved to be exactly ten grains heavier than when it was placed in the retort; showing that the ten grains of air that had disappeared had combined with the metal during calcination.  This experiment, then, decided against phlogiston, and led to an analysis of common air confirming Priestley’s discovery of oxygen.

(4) An hypothesis must agree with the rest of the laws of Nature; and, if not itself of the highest generality, must be derivable from primary laws (chap. xix.  Sec. 1).  Gravitation and the diffusion of heat, light and sound from a centre, all follow the ‘law of the inverse square,’ and agree with the relation of the radius of a sphere to its surface.  Any one who should think that he had discovered a new central force would naturally begin to investigate it on the hypothesis that it conformed to the same law as gravitation or light.  A Chemist again, who should believe himself to have discovered a new element, would expect it to fill one of the vacant places in the Periodic Table.  Conformity, in such cases, is strong confirmation, and disagreement is an occasion of misgivings.

A narrower hypothesis, as ‘that the toad’s ugliness is protective’, would be supported by the general theory of protective colouring and figure, and by the still more general theory of Natural Selection, if facts could be adduced to show that the toad’s appearance does really deter its enemies.  Such an hypothesis resembles an Empirical Law in its need of derivation (chap. xix.  Sec.Sec. 1, 2).  If underivable from, or irreconcilable with, known laws, it is a mere conjecture or prejudice.  The absolute leviation of phlogiston, in contrast with the gravitation of all other forms of matter, discredited that supposed agent.  That Macpherson should have found the Ossianic poems extant in the Gaelic memory, was contrary to the nature of oral tradition; except where tradition is organised, as it was for ages among the Brahmins.  The suggestion that xanthochroid Aryans were “bleached” by exposure during the glacial period, does not agree with Wallace’s doctrine concerning the coloration of Arctic animals.  That our forefathers being predatory, like bears, white variations amongst them were then selected by the advantage of concealment, is a more plausible hypothesis.

Although, then, the consilience of Inductions or Hypotheses is not a sufficient proof of their truth, it is still a condition of it; nonconsilience is a suspicious circumstance, and resilience (so to speak), or mutual repugnance, is fatal to one or all.