132 THE SCIENCE OF LOGIC 



perceptible or picturable factors, and without the aid of purely con 

 ceptual or intelligible factors, such as force, power, efficiency, pur 

 pose and design, have proved futile; that concepts of hyperphysical 

 entities and influences, however &quot; occult &quot; to sense or imagination, 

 are indispensable for a rational explanation of nature s processes ; 

 in a word, that the cause or principle of action which may be the 

 object of a legitimate scientific hypothesis need not be itself a pheno 

 menon, directly perceptible by the senses. 



It must, however, be such an agency, or group of agencies, that, 

 though not directly perceptible itself, it is perceptible in its effects : 

 it must be supposed to dwell in phenomena, to become operative 

 in certain combinations of phenomena, and to produce therein directly 

 perceptible effects. This indirect perceptibility of the supposed 

 causes, in their effects, is necessary and sufficient for the object of 

 a scientific hypothesis. In this way alone are &quot;atoms,&quot; &quot;elec 

 trons,&quot; &quot; ions,&quot; &quot; sub-atomic motions,&quot; &quot; biophors,&quot; and all the 

 infinitesimally minute &quot;causes &quot; of modern scientific hypotheses, 

 perceptible or &quot; phenomenal &quot; : in their effects, in the phenomena 

 which they are supposed to actuate or constitute ; and in this 

 they differ in no way from the &quot; materia prima&quot; &quot;forma sub- 

 stantialis&quot; &quot;qualities,&quot; &quot;forces,&quot; &quot;faculties,&quot; &quot;natures,&quot; &quot;pro 

 perties,&quot; etc., of Scholasticism: for these too are perceptible 

 indirectly, in their effects. 



Properly speaking, all such explanatory factors of our experience are 

 &quot; intelligible &quot; or &quot; noumenal,&quot; rather than &quot; sensible &quot; or &quot; phenomenal &quot;. 

 The need that impels us to look for an explanation of sense experience obliges 

 us to conjecture or suppose the real existence and operation of such really 

 supra-sensible agencies. The whole process of conceiving the latter, and 

 reasoning from such conceptions, is a process of the faculty which transcends 

 the faculties of sense the intellect. It makes comparatively little difference 

 whether these conceptions, these hypothetical &quot; causes,&quot; are more or less im 

 mersed in, and supported by, concrete imagination-pictures. 1 The visible, 



1 It might, perhaps, be argued that hypotheses having for their objects abstract 

 &quot; powers,&quot; &quot; forces,&quot; &quot; natures,&quot; etc., in phenomena, cannot be so accurately verifi 

 able, nor, therefore, so fruitful to science, as hypotheses which contemplate only 

 such directly calculable factors as &quot; atoms,&quot; &quot; electrons,&quot; &quot; undulations,&quot; etc. This 

 is scarcely true, for mathematical values may be assigned to the former as easily as 

 to the latter. It cannot be said that the British scientists have in any striking way 

 excelled the French in their contributions to science ; yet the former have been always 

 far more addicted than the latter to concrete, picturable, mechanical conceptions. 

 C/. DUHEM, Evolution de la mecanique (Paris, 1903, ch. xv.) ; Professor Windle s 

 article in the Dublin Review, already mentioned ; art. on &quot; The Contrast of English 

 and French Concepts of Physical Theories,&quot; by the Rev. P. DE VREGILLK in the 

 Month, April, 1907, pp. 350 sqq. ; H. POINCARE S Science and Hypothesis (Eng. 



