De reriini mitura}* Atoms from the loadstone push 

 away the air and tend to cause a vacimm to form 

 outside the loadstone. The structure of iron is such 

 that it, unlike other materials, can be pushed into 

 this empty space by the throni^ine; atoms of air be- 

 yond it. 



Galen " returned to a quasi-animistic solution in 

 his denial of Epicurus' ara;ument, which he stated 

 somewhat difierently from Lucretius. One can infer 

 that Galen held that all things have, to a greater or 

 lesser degree, a sympathetic faculty of attracting \\s 

 specific, or proper, cjuality to itself.'" The loadstone 

 is only an inanimate example of what one finds in 

 nutritive organs in organic beings. 



One of the few writers whose explanations of the 

 loadstone Gilbert mentioned with approval is St. 

 Thomas Aquinas. Although the medieval scholastic 

 philosophy of St. Thomas seems foreign to our way 

 of thinking, it formed a background to many of Gil- 

 bert's concepts, as well as to those of his predeces.sors. 

 and it will assist our di.scusslon to consider briefly 

 Thomist philosophy and to make its terminology 

 explicit at this point. '^ 



In scholastic philosophy, all beings and substances 

 arc a coalescence of inchoate matter and enacting 

 form. Form is that which gives being to matter and 

 which is responsible for the "virtus" or power to cau.se 

 change, since matter in itself is inert. Moreover, 

 forms can be grasped intellectually, whence the 

 nature of a being or a substance can be known. Any 

 explanation of phenomena has to be based upon 

 these innate natures, for only if the nature of a sub- 

 stance is known can its properties be understood. 

 Inanimate natures are determined by observation, 

 abstraction, and induction, or by classification." 



The nature of a substance is causally prior to its 

 properties; while the definition of the nature is logi- 

 cally prior to these properties. Thus, what we call 



'* Lucretius, De rerum natura, translated by \V. H. D. Rouse, 

 Loeb Classical Library, London, 1924, bk. VI, lines 998-1041. 



'* Galen, On the natural /acuities, translated by A. S. Brock, 

 Loeb Classical Library, London, 1916, bk. 1 and bk. 3. A 

 view similar to tliis appeared in Plato, Timaeus, 81 (sec foot- 

 note 13). 



" This same concept was to reappear in the Middle Ages as 

 the inclinatio ad simile. 



" The background for much of tlie following was derived 

 from Annalicsc Maier, An der Grenze von Scholaslik und j\'alur- 

 wissenchajt, ed 2, Rome, 1952. 



" St. Thomas' epistemology for the natural inanimate world 

 was based upon Aristotle's dictum: that which is in the mind 

 was in the senses first. 



the theory of a substance is expressed in its defini- 

 tion, and its properties can be deduced from this 

 definition. 



The world of St. Thomas is not a static one, but 

 one of the .Aristotelian motions of quantity (change 

 of size), of quality (alteration), and of place (loco- 

 motion) . Another kind of change is that of substance, 

 called generation and corruption, but this is a muta- 

 tion, occurring instantly, rather than a motion, that 

 requires time. In mutation the essential nature is 

 replaced by a new substantial form. 



.Ml these changes are motivated by a causal hier- 

 archy that extends from the First Cause, the "Dator 

 Formarum," or Creator, to .separate intellectual sub- 

 stances that may be angels or demons, to the celestial 

 bodies that are the "generantia" of the substantial 

 forms of the elements and finally to the four prime 

 qualities (dry and wet, hot and cold) of the substantial 

 forms. Accidental forms are motivated by the sub- 

 stantial forms through the instrumentality of the four 

 prime qualities, which can only act by material 

 contact. 



The only causal agents in this hierarchy that are 

 learned through the senses are the tangible qualities. 

 Usually the prime qualities are not observed directly, 

 but only other qualities compounded of them. One 

 of the problems of scholastic philosophy was the 

 incorporation, into this system of efficient agents, 

 of other qualities, such as the qualities of gravity 

 and levity that are responsible for upward and down- 

 ward motion. 



Besides the causal hierarchy of forms, the natural 

 world of St. Thomas existed in a substantial and spatial 

 hierarchy. .\11 substances whether an element or a 

 mixture of elements have a place in this hierarchy 

 by virtue of their nature. If the material were re- 

 moved from its proper place, it would tend to return. 

 In this manner is obtained the natural downward 

 motion of earth and the natural upward motion 

 of fire. 



Local motion can also be caused by the '"virtus coeli" 

 generating a new form, or through the qualitative 

 change of alteration. Since each element and mixture 

 has its own natural place in the hierarchy of material 

 substances, and this place is determined by its nature, 

 changes of nature due to a change of the form can 

 produce local motion. If before change the substance 

 is in its natural place, it need not be aftcnvards, 

 and if not, would then tend to move to its new 

 natural place. 



It will be noted that the scholastic explanation of 



PAPER 8: NATURAL PHILOSOPHY OF WILLIAM GILBERT 



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