BOOK I. 



APPLICATIONS OF THE PHENOMENA AND 

 LAWS OF WEIGHT. 



is no part of human activity dealing with matter in which 

 J- the weight of bodies, whether they are solid, liquid, or gaseous, 

 does not enter, and in which therefore the effects of weight have not 

 to be taken into account and to be calculated, This is as necessary 

 for equilibrium as for motion. Thus notably such constructions as 

 monuments, public and private buildings, bridges, aqueducts, and 

 those movable bodies used in land, river, and sea transport, together 

 with apparatus, engines, and tools of all kinds, may with good right 

 be considered from the point of view of equilibrium or stability and 

 of motion as so many physical applications, and especially as appli- 

 cations of the phenomena and laws of weight. 



But one can easily understand that we in no way intend to carry 

 out so large a survey. The meaning we shall give to physical appli- 

 cations is much more restricted : we shall refer only to those of which 

 the principle is borrowed from physics, to the forces and to the la\vs 

 which these forces manifest, leaving on one side the numerous appli- 

 cations which depend exclusively upon Mechanics. Tin's remark 

 applies to all branches of physics, but in this First Book devoted to 

 Weight we shall only pass under review and describe those appli- 

 cations, or machines based upon some of the laws of gravity, such, 

 for instance, as the constancy of the direction of this force on the 

 surface of the earth ; the energy developed in a body which falls 

 from a height ; the isochronous oscillations of pendulums ; atmospheric 

 pressure, and the like. Further, we shall deal chiefly with those 



