102 DISSERTATION SECOND. [part t. 



quiries. In a treatise which bears the date of 1577, he re- 

 duced the pulley to the lever ; but with respect to the 

 inclined plane, he continued in the same errour with Pap- 

 pus Alexandrinus, supposing that a certain force must be 

 applied to sustain a body, even on a plane which has no 

 inclination. 



Stevinus, an engineer of the Low Countries, is the first 

 who can be said to have passed beyond the point at which 

 the ancients had stopped, by determining accurately the 

 force necessary to sustain a body on a plane inclined at 

 any angle to the horizon. He resolved also a great num- 

 ber of other problems connected with the preceding, but, 

 nevertheless, did not discover the general principle of the 

 composition of forces, though he became acquainted with 

 this particular case, immediately applicable to the inclined 

 plane. 



The remark, that a chain laid on an inclined plane, with 

 a part of it hanging over at top, in a perpendicular line, 

 will be in equilibrio, if the two ends of the chain reach 

 down exactly to the same level, led him to the conclusion, 

 that a body may be supported on such a plane by a force 

 which draws in a direction parallel to it, and has to the 

 weight of the body the same ratio that the height of the 

 plane has to its length. 



Though it was probably from experience that Stevinus 

 derived the knowledge of this proposition, he attempted to 

 prove the truth of it by reasoning a priori. He suppos- 

 ed the two extremities of the chain, when disposed as 

 above, to be connected by a part similar to the rest, which, 

 therefore, must hang down, and form an arch. If in this 

 state, says he, the chain were to move at all, it would con- 

 tinue to move for ever, because its situation, on the whole, 

 never changing, if it were determined to move at one in- 

 stant, it must be so determined at every other instant. 



