352 APPENDIX I 



could not be comprehended by the imagination. . . . This 

 ought not to seem wonderful, for it is the nature of foundations 

 to be humble, but if they are securely laid, great masses arise 

 upon them. Accordingly, when I as yet acknowledged the 

 jurisdiction of imagination alone in regard to material things, 

 I was of opinion that any natural inertia in bodies was 

 unintelligible, and that a body at rest in vacuo or in a free 

 space must receive the velocity of another, however small that 

 other might be ; and that this does not actually happen in our 

 experience I attributed to the system established by the wisdom 

 of the Supreme Author of things, in which all things are ruled 

 by the most just laws. Nor indeed did I doubt that the origin 

 of the system might be rationally thought out on mechanical 

 principles from those very laws of natural bodies, which explain 

 occurrences by the composition of motions, such as I expounded 

 regarding several cases in a treatise which I published when 

 a young man.' Phoranomus, see Arch. f. Gesch. d. Phil. i. 577. 

 'When I was a young man and, at that time, following 

 Democritus and his adherents in this matter, Gassendi and 

 Descartes, I regarded the nature of body as consisting in mere 

 inert mass, I issued a treatise with the title Hypothesis Physica, 

 in which I expounded a theory of motion both abstract (inde- 

 pendent of the system of things) and concrete (as it appears 

 in the system of things), which I see has pleased many 

 distinguished men better than its moderate worth deserved. 

 In this treatise I maintained that, supposing my view of the 

 nature of body to be right, every impinging body gives its 

 impulse [conatus] to the body on which it impinges or which 

 is directly in its way, as such. For when the impact takes 

 place, the body impinged upon endeavours to move forward 

 and thus to go away, and (since, as I then thought, body is 

 indifferent to motion or rest) this endeavour [effort, conatus] 

 must have its full effect in the body impinged upon, unless it 

 is hindered by an opposite effort, and even if it is so hindered, 

 since these different efforts must be compounded together. 

 Accordingly it was manifest that no cause can be given why 

 the impinging body should not achieve the effect towards 

 which it tends or why the body impinged upon should not 

 receive the whole impulse [conatus] of the impinging body, and 

 therefore the motion of the body impinged upon is compounded 

 of its own original impulse and the new or foreign impulse it 

 has received. Whence I further showed that if in body there 



