28 HISTORY OF MECHANICS. 



in any direction. If the First Law of Motion had 

 been clearly known, it would then, perhaps, have 

 been seen that the way to understand and analyze 

 the motion of any body, is to consider the Causes 

 of change of motion which at each instant operate 

 upon it ; and thus men would have been led to 

 the notion of Accelerating Forces, that is, Forces 

 which act upon bodies already in motion, and acce- 

 lerate, retard, or deflect their motions. It was, how- 

 ever, only after many attempts that they reached 

 this point. They began by considering the whole 

 motion with reference to certain ill-defined abstract 

 Notions, instead of considering, with a clear ap- 

 prehension of the conditions of Causation, the suc- 

 cessive parts of which the motion consists. Thus, 

 they spoke of the tendency of bodies to the Center, 

 or to their Own Place; of Projecting Force, of 

 Impetus, of Retraction; with little or no profit 

 to knowledge. The indistinctness of their notions 

 may, perhaps, be judged of from their specula- 

 tions concerning projectiles. Santbach 5 , in 1561, 

 imagined that a body thrown with great velocity, 

 as, for instance, a ball from a cannon, went in a 

 straight line till all its velocity was exhausted, and 

 then fell directly downwards. He has written a 

 treatise on gunnery, founded on this absurd assump- 

 tion. To this succeeded another doctrine, which, 



5 Problematum Astronomicorum et Geometricorum Secliones, 

 vii. &c. &c. Auctore Daniele Santbach, Noviomago. Basileu 1 , 

 1561. 



