294 ^^^ POPULAR SCIENCE MONTHLY. 



tli« theologus^ there was a sort of no-Man's land, which profane per- 

 sons might enter into and possess. For Aquinas goes on : " Non autem 

 ex parte corporis, nisi secundum habitudinem quam habet corpus ad 

 animam." ^ That is to say, while the anima intellectiva (intellective 

 soul), which issues directly from the hand of God, is the exclusive 

 province of the theologian, the anima sensitiva (sensitive soul), which 

 is proj)agated in a physical manner,*^ the passions, and the appetites, 

 may be left to the uncowled cultivator of science as not requiring the 

 help of divine inspiration. It was at any rate in this field that the 

 foundations of inductive psychology were laid, and it was to the ex- 

 planation of the simpler phenomena of sensibility that physical con- 

 ceptions were first applied. The two greatest thinkers of the seven- 

 teenth century were almost simultaneously on the ground. 



Descartes is not now remembered by his " Treatise on the Pas- 

 sions " (which was published within a year of Hobbes's work on " Hu- 

 man Nature" ), and we only note it here as an early example of ex- 

 perimentalism in Psychology. We are more concerned to observe 

 that his vindication of the immateriality of the thinking principle, and 

 his clear perception of the unity of the mental aggregate, were almost 

 contemporaneous with the "new geometry." We are not, indeed, 

 solicitous with regard to Descartes to justify our thesis — that each 

 advance in Psychology has been caused and conditioned by a corre- 

 sponding and previous advance in physical science ; for the enuncia- 

 tion of the Cartesian principle was less a fact in Psychology than the 

 accomplishment of a stadium in the metaphysical evolution, which 

 made Psychology ^^ossible. But, perhaps, it may not seem fanciful 

 to mention that Cavalieri, " the generally reputed father of the new 

 geometry," published in 1635 his Method of Indivisibles (which had 

 been largely anticipated by Kepler), or to connect his leading prin- 

 ciple — that a solid is generated out of an infinite number of sur- 

 faces placed one above another as their indivisible elements — with the 

 effort to unite into a single substance, itself localized, the endless mul- 

 tiplicity of the mental manifestations. It is, at least, clear, that the 

 application of physics to mind will follow the development of physics ; 

 and as physics has not yet advanced beyond the geometrical stage, as 

 the period immediately preceding " Descartes's Meditations " was the 

 epoch of a great geometrical advance, as we now know that in virtue 

 of the co?ise?isus (mutual agreement) wliich governs all social phenom- 

 ena, all the conceptions of any age are moulded in the same matrix, it 

 seems not wholly imaginary to adduce the psychology of Descartes, 

 who was himself an eminent geometer, as in some degree the result of 

 the dominance of the earliest developed of the sciences. 



Emerging from this doubtful region, we pass on to the terra firma 

 (firm ground) of demonstrable fact. Hobbes was rather older than 

 Descartes, but he had the advantage of delaying at least the publica- 

 ^ " Sura. Theol," pt. i., qu. Ixxv. 2 YtA^ ^ ^^ cxviii., art. i. 



