LECTURES. 199 



spect of solid, liquid, and aeriform bodies. Continued motion of the 

 planets. 



Causes of cessation of motion. Friction ; resistance ; and communi- 

 cation of motion to other bodies. Ball on cloth ; also on smooth 

 board. Wheel on friction rollers. 



Matter perfectly free to move. Large mass freely suspended, put in 

 motion by impulses from small ball of putty; velocity small in pro- 

 portion. 



Effect of a succession of small impulses. Heavy body put in rapid 

 motion by successive pulls with cambric thread. 



Attempt to put a body in a state of rapid motion by a single given 

 impulse. 



Motion of large mass stopped by a succession of small impulses. 

 Also_, by a single impulse, or by an obstacle. 



Term vis-inertice sometimes used in connexion with this phenomenon. 



Tendency of matter to move in a straight line, shown by an ex- 

 periment. 



Experimental proof of uniform velocity of unrestrained motion. 



Animals sometimes act instinctively in accordance with the prin- 

 ciple of inertia. Hare when pursued by the hounds. Rams in 

 butting. Favorite amusement at the court of Persia. 



Means of accumulating momentum in a large mass of matter for 

 purposes in the arts. 



ATTRACTION AND REPULSION, OR THE GENERAL PHYSICAL FORCES. 



(45.) The tendency in the parts of all matter to approach toward 

 or to recede from each other. 



These tendencies differ from the other general properties of matter, 

 in the fact of their being forces acting reciprocally between bodies at 

 a distance from each other, or between the minute parts of the same 

 body. The existence of these forces, in the present state of science is 

 an ultimate fact, although attempts have been made to refer them 

 to the intermediate agent or agents of the phenomena of heat and 

 electricity. 



The intensity of the attracting and repelling forces varies with the 

 distance of the parts of matter between which they act, and where 

 the geometrical relation between the distance and the intensity is 

 known, the whole is called a law of attraction. 



In the present state of knowledge we arrange the different pheno- 

 mena of attraction and repulsion, under the following heads, although 

 it is not impossible that they may be the result of one principle. 



Atraction of 



GRAVITATION, 1 which act 



ELECTRICITY, \ at sensible 



MAGNETISM, J distances. 



COHESION, 

 ADHESION, 

 CAPILLARITY, 

 CHEMICAL AFFINITY, 



which act 

 > at insensible 

 distances. 



