316 HISTORY OF MECHANICS. 



danus and Tartalea. 2 No progress was likely to occur, till the mathe- 

 maticians had distinctly recovered the genuine Idea of Pressure, as a 

 Force producing equilibrium, which Archimedes had possessed, an<? 

 which was soon to reappear in Stevinus. 



The properties of the Lever had always continued known to mathe- 

 maticians, although, in the dark period, the superiority of the proof 

 given by Archimedes had not been recognized. We are not to be 

 surprised, if reasonings like those of Jordanus were applied to demon- 

 strate the theories of the Lever with apparent success. Writers on 

 Mechanics were, as we have seen, so vacillating in their mode of deal- 

 ing with words and propositions, that their maxims could be made to 

 prove any thing which was already known to be true. 

 . We proceed to speak of the beginning of the real progress of Me- 

 chanics in modern times. 



Sect. 2. Revival of the Scientific Idea of Pressure. Stevinus. 

 Equilibrium of Oblique Forces. 



THE doctrine of the Centre of Gravity was the part of the mechan- 

 ical speculations of Archimedes which was most diligently prosecuted 

 after his time. Pappus and others, among the ancients, had solved 

 some new problems on this subject, and Commandinus, in 1565, pub- 

 lished De Centra Gravitatis Solidorum. Such treatises contained, for 

 the most part, only mathematical consequences of the doctrines of 

 Archimedes ; but the mathematicians also retained a steady conviction 

 of the mechanical property of the Centre of Gravity, namely, that all 

 the weight of the body might be collected there, without any change 

 in the mechanical results; a conviction which is closely connected 

 with our fundamental conceptions of mechanical action. Such a prin- 

 ciple, also, will enable us to determine the result of many simple me- 

 chanical arrangements ; for instance, if a mathematician of those days 

 had been asked whether a solid ball could be made of such a form, 

 that, when placed on a horizontal plane, it should go on rolling forwards 

 without limit merely by the effect of its own weight, he would proba- 

 bly have answered, that it could not ; for that the centre of gravity of 

 the ball would seek the lowest position it could find, and that, when it 

 had found this, the ball could have no tendency to roll any further. 

 And, in making this assertion, the supposed reasoner would not be an- 



8 Ubaldi mentions and blames Jordanus's way of treating the Lever. (See his 

 Preface.) 



