FERGUSON'S LECTURES. 



LECT. A second property of matter is inactivity or passive- 

 v^x-v-x-; ness ; by which it always endeavours to continue in the 

 Inactivity. gtate t jj at j t j s j n ^ whether of rest or motion. And there- 

 fore, if one body contains twice or thrice as much mat- 

 ter as another body does, it will have twice or thrice as 

 much inactivity ; that is, it will require twice or thrice 

 as much force to give it an equal degree of motion, or 

 to stop it after it hath been put into such a motion. 



That matter can never put itself into motion is allow- 

 ed by all men. For they see that a stone, lying on the 

 plane surface of the earth, never removes itself from that 

 place, nor does any one imagine it ever can. But most 

 people are apt to believe that all matter has a propensity 

 to fall from a state of motion into a state of rest ; because 

 they see that if a stone or a cannon-ball be put into 

 ever so violent a motion, it soon stops ; not considering 

 that this stoppage is caused, 1. By the gravity or 

 weight of the body, which sinks it to the ground in 

 spite of the impulse ; and, 2. By the resistance of the 

 air through which it moves, and by which its velocity is 

 retarded every moment till it falls. 



A bowl moves but a short distance upon a bowling- 

 green ; because the roughness and unevenness of the 

 grassy surface soon creates friction enough to stop it. 

 But if the green were perfectly level, and covered with 

 polished glass, and the bowl were perfectly hard, round, 

 and smooth, it would go a great way farther, as it would 

 have nothing but the air to resist it ; if then 'the air were 



meaning differing very materially from that of our author in the above 

 paragraph ; who would shew rather that as every thing which is mate- 

 rial must possess length, breadth, and thickness, these propert.es car 

 not exist without the occupation of space, and as such, that evea 

 which is invisible, and eludes the grasp, no less than the i 

 of the philosopher, may be so compressed as to attain a perfectly s, 

 form To illustrate experimentally the materiality of air it is merely 

 necessary to invert a wine glass in I "essel of water, and the . 

 Tm fluid within, will prevent the introduction of the water, wluch 

 would enter immediately if the air was allowed to escape. 



