314 HISTORY OF MECHANICS. 



move the obstacle, and the direction in -which it really does move 

 Thus the Wedge and the Inclined Plane are connected in principle. 

 He also refers the Screw to the Inclined Plane and the Wedge, in a 

 manner which shows a just apprehension of the question. Benedetti 

 (1585) treats the W^edge in a different manner: not exact, but still 

 showing some powers of thought on mechanical subjects. Michael 

 Varro, whose Tractatus de Motu was published at Geneva in 1584, 

 deduces the wedge from the composition of hypothetical motions, in a 

 way which may appear to some persons an anticipation of the doctrine 

 of the Composition of Forces. 



There is another work on subjects of this kind, of which several edi- 

 tions were published in the sixteenth century, and which treats this 

 matter in nearly the same way as Varro, and in favor of which a claim 

 has been made 1 (I think an unfounded one), as if it contained the true 

 principle of this problem. The work is " Jordanus Nemorarius De 

 Ponderositate? The date and history of this author were probably 

 even then unknown; for in 1599, Benedetti, correcting some of the 

 errors of Tartalea, says they are taken " a Jordano quodam autiquo." 

 The book was probably a kind of school-book, and much used ; for an 

 edition printed at Frankfort, in 1533, is stated to be Cum gratia et 

 privilegio Imperiali, Petro Apiano mathematico Ingolstadiano ad xxx 

 annos concesso. But this edition does not contain the Inclined Plane. 

 Though those who compiled the work assert in words something like the 

 inverse proportion of Weights and their Velocites, they had not learnt 

 at that time how to apply this maxim to the Inclined Plane ; nor were 

 they ever able to render a sound reason for it. In the edition of Ven- 

 ice, 1565, however, such an application is attempted. The reasonings 

 are founded on the Aristotelian assumption, " that bodies descend more 

 quickly in proportion as they are heavier." To this principle are add- 

 ed some others ; as, that " a body is heavier in proportion as it de- 

 scends more directly to the centre," and that, in proportion as a body 

 descends more obliquely, the intercepted part of the direct descent is 

 smaller. By means of these principles, the "descending force" ot 

 bodies, on inclined planes, was compared, by a process, which, so far 

 as it forms a line of proof at all, is a somewhat curious example ot 

 confused and vicious reasoning. When two bodies are supported on 

 two inclined planes, and are connected by a string passing over the 

 junction of the planes, so that when one descends the other ascends, 



i Mr. Drinkwater's Life of Galileo, in the Lib. Usef. Kn. p. S3. 



