Lesson XIII.] GRAVITY, WEIGHT, Sec. 6l 



concluded that bodies the most compact, and which 

 consequently contain a greater number of particles 

 in the same bulk, will weigh more than others; be- 

 cause the weight being the sum of the velocities 

 impressed on all the particles, that sum must be so 

 much the greater, as there are more material par- 

 ticles contained in the mass of the body. 



From what is here said, I would observe with 

 M. de Condorcet, that we may see " the necessity 

 " of carefully distinguishing between the effect of 

 " Gravity, and that of Weight : the former is the 

 t( power of transmitting, or a tendency to trans- 

 " tnit, into every particle of matter a certain velo- 

 <c city which is absolutely independent on the 

 " number of material particles; and the second is 

 " the effort which must be exercised to prevent a 

 " given mass from obeying the law of Gravity. 

 *' Weight accordingly depends on the mass, lut 

 " Gravity has no dependence at all upon it." 



Again, with respect to the difference between 

 Heaviness and Weight, taken in their literal sense, 

 heaviness is that quality in a body which we feel, 

 and distinguish by itself: weight is the measure 

 >nd degree of that quality which we cannot as- 

 certain but by comparison. We say absolutely, 

 and in an undetermined sense, that a thing is 

 heavy ; but relatively, and in a determined man- 

 ner, that it is of such a weight ; for example, of 

 two, three, or four pounds. A thousand circum- 

 stances prove the heaviness of the air, for instance; 

 but the mercury in the barometer determines its 

 exact weight* 



LESSON 



