ESSENTIAL AND PECULIAR. 5, 



The change of distance between one material body and another, or, in 

 other words, their approach to or separation from each other, is called 

 MOTION ; and the wide expanse in which motion of any kind is performed, is de 

 nominated SPACE. 



Matter has its ESSENTIAL, and its PECULIAR PROPERTIES. Its essential 

 properties are those which are common to it under every form or mode ol 

 combination. Its peculiar properties are those which only appertain to it un 

 der definite forms or definite circumstances. 



The ESSENTIAL PROPERTIES of matter are usually classed under the six follow 

 ing heads : passivity, extension, density, impenetrability, divisibility, and gravi 

 tation ; which, however, may easily be reduced to four, since extension, density 

 and impenetrability, may be comprehended under the general term cohesibility 



PASSIVITY, inertia or visinerticE,, is the tendency in a body to persevere in a 

 given state, whether of rest or motion, till disturbed by a body of superiot 

 force. And hence these terms, which are mere synonymes, imply a power of 

 mobility as well as a power of quiescence ; although passivity has often been 

 confined to quiescence, while mobility has been made a distinct property 

 Thus it is from the same power, or tendency to passivity, that a cannon ball 

 continues its motion after being projected from a gun, as that by which it re- 

 mained at rest before it was thrown off; for it is a well known theorem in pro- 

 jectiles, that the action of the powder on a bullet ceases as soon as the bullet 

 is out of the piece In like manner a billiard ball at rest will continue so till 

 put into motion by a billiard ball in motion, for it can never commence motion 

 of its own accord While a billiard ball in motion would persevere in motion, 

 and in the same velocity of motion, for ever, if it met with no resistance. 

 But it does meet with resistance from a variety of causes, as the friction of 

 the atmosphere, the friction of the green cloth, and at last a contact with one 

 of the sides of the table, or with the ball against which it is directed. 



In this last case either ball will receive conversely the same precise pro- 

 portion of rest or motion which it communicates. Thus, if the ball in motion 

 strike the ball at rest obliquely, the latter will be put into a certain degree of 

 activity, and the former will, in the very same degree, be impeded in its pro- 

 gress, and receive an equal tendency to a state of rest. If the latter, on the 

 contrary, by what is significantly called a dead stroke, receive the whole 

 charge of motion which belongs to the former, it will give to the former, in 

 like manner, the whole possession of its quiescence, and the state of each 

 will be completely reversed : the ball hitherto at rest proceeding with all the 

 velocity of that hitherto in motion, and the ball hitherto in motion exhibiting 

 the dead stand of that hitherto at rest. 



So, if it were possible to place an orb quietly in some particular part of 

 space, where it would be equally free from the attractive influence of every 

 one of the celestial systems, it would, from the same tendency to inertitude, 

 remain quiescent and at rest for ever. While, on the contrary, if a body 

 were to be thrown from any one of the planets by the projectile force of a 

 volcano, or of any other agency, beyond the range of the attractive or centripetal 

 power of such planet, it would continue the same velocity of motion for ever 

 which it possessed at the moment of quitting the extreme limit of the planet's 

 influence ; unless in its progress it should encounter the influence of some other 

 planet ; and in this last case it would be either drawn directly into contact 

 with the planet it thus casually approached, or would have its path inflected 

 into a circle, and revolve around it as a satellite, according to its velocity, 

 and the relative direction of its course at the moment the planetary influence 

 began to take effect. Thus a body projected horizontally to the distance of 

 about 4.35 miles from the earth's surface, provided there were no resistance 

 in the atmosphere, would not fall back again, but become a satellite to the 

 earth, and perpetually revolve around it at this distance. The moon is sup- 

 posed to have no atmosphere, or, at the utmost, one rarer than we can pro- 

 duce with our best air-pumps : she is also supposed to possess larger and 

 more active volcanoes than any which are known to exist on the earth. And 

 hence it requires no great stretch of imagination to conceive that bodies 



