that all Matter is Heavy. 261 



5. Suppose two bodies, A and B, to be endowed with reciprocal 

 attraction ; or, in other words, to gravitate towards each other. 

 Being placed at a distance, and then allowed to approach, if, after 

 any given time, it were found that they had moved severally 

 any ascertained distances, evidently their relative inertias would 

 be considered as inversely as those distances. 



6. In the next place, let us suppose two bodies, X and Y, en- 

 dowed with the opposite force of reciprocal repulsion, to be placed 

 in proximity, and then allowed to fly apart. The distances run 

 through by them severally, being, at any given time, determined, 

 might not their respective inertias be taken to be inversely as those 

 distances ; so that the question would be as well ascertained in 

 this case, as in that above stated in which gravitation should be 

 resorted to as the test ? 



7. Jt seems to me that this question is sufficiently answered, in 

 the affirmative, in your second paragraph, page 7, (p. 269,) in 

 which you allege, that " one body has twice as much inertia as 

 another, if when the same force acts upon it for the same time, 

 it acquires hut half the velocity. This is the fundamental con- 

 ception of inertia.''^ 



8. In the third paragraph, fourth page, (p. 261,) you say, ^Hhat 

 the quatitity of matter is measured hy those sensible properties of 

 matter ichich undergo quantitative addition, subtraction and di- 

 vision, as the matter is added, subtracted or divided, the quan- 

 tity of matter cannot be known in any other way ; but this mode 

 of measuring the quantity of matter in order to be true at all, 

 must be true universally.^^ 



9. Also your fourth paragraph, fifth page, (p. 268,) concludes 

 with this allegation, " and thus lae have proved, that if there be 

 any kind of matter which is not heavy, the weight can no longer 

 avail us, in any case to any extent, as the measure of the quan- 

 tity of matter. ^^ 



10. In reply to these allegations let me inquire, cannot a matter 

 exist of which the sensible properties do not admit of being 

 measured by human means ? Because some kinds of matter 

 can be measured by " those sensible qualities which undergo 

 quantitative addition, subtraction and division," does it follow 

 that there may not be matter which is incapable of being thus 

 measured ? And wherefore would the method of obtaining phi- 



