HYPOTHESIS I39 



he describes them, afford the only possible or conceivable explanation of those 

 phenomena. 



Again, are vegetable and animal species fixed, or transformable ? Let a 

 naturalist suppose them to be transformable. He must proceed to experiment 

 on some cause supposed to be capable of effecting the transformation from 

 some one specific type to a different type, and so submit his supposition to the 

 control of facts. What might such a cause be ? A possible cause is sug 

 gested by the phenomena of artificial selection, and artificial cultivation or 

 rearing, which are found to be productive of new varieties and races. Darwin 

 observed those phenomena carefully and minutely, and then made the sup 

 position that there are at work in nature agencies analogous to those em 

 ployed by the artificial breeder, and capable of producing not merely new 

 varieties or races, but new species. Now, if there are really in nature some 

 such agencies, they can become the object of scientific hypotheses, and their 

 mode of action may be described after the analogy of the intelligent artificial 

 selection, or intelligent sorting, of the breeder as &quot; natural selection &quot;. But it 

 remains an open question whether the actual existence of such transforming 

 agencies in nature if there are such can ever be verified : and until their 

 existence and mode of operation are at least shown to be capable of verification, 

 the hypothesis will remain a mere systematic conception, an &quot; idee directrice,&quot; ] a 

 methodological view of the world of living things, rather than a &quot; scientific &quot; 

 hypothesis. 



Similarly, such an hypothesis as Weismann s germ-plasm theory to account 

 for the fact of heredity, can scarcely be regarded as a scientifically verifiable 

 hypothesis, involving, as it does, elements admittedly beyond the range of all 

 possible experience. Professor Windle, writing about it in the Dublin Review* 

 remarks that &quot; the theory is a tolerably complex one to be built upon a system 

 of vital units which no one has ever seen or ever can demonstrate &quot;. 



Yet another instance of the same unsatisfactory class of conceptions is 

 that of Sir William Crookes, regarding the renovation of energy in the universe : 

 &quot; that the heat radiations propagated outwards ... are transformed at the 

 confines of the universe into the primary the essential motion of chemical 

 atoms, which . . . gravitate inwards, and thus restore to the universe the 

 energy which would be lost to it through radiant heat.&quot; 3 



On the other hand, a good example of a thoroughly scientific hypothesis, 

 afterwards experimentally verified beyond any possibility of doubt by the 

 &quot; method of difference &quot; (241), was Pasteur s supposition that the fermentation of 

 the grape was due to germs that settled on it, and not to mere chemical action. 

 He first extracted the juice from the interior of the grape without allowing it 

 to come into contact with the exterior covering, or with the air, sealed it her 

 metically in tubes, and found that it did not ferment. Again, in the month of 

 June before the appearance of the coating of germ-cells, which begins in 

 July he carefully surrounded certain grape-clusters with wadding, and so pro 

 tected them from the germs. The grapes of those bunches were pressed and 

 the juice obtained refused to ferment. 



Equally convincing, perhaps, were the experiments of the same eminent 



1 MERCIER, op. cit., p. 340, from which context the above example is taken. 



2 April, 1906, p. 334 (italics ours). 



3 apud GERARD, The Old Riddle and the Newest Answer, p. 26. 



