MOT 



MOU 



place of a body, or of any parts of a body ; 

 for, in the cases of a globe turning on its 

 axis, and of a wheel revolving on a pivot, 

 the parts of these bodies change their 

 places, while the bodies themselves re- 

 main stationary. 



1. Uniform motion is that of a body 

 which passes over equal spaces in equal 

 times. It is produced by a force having 

 acted on a body once, and having ceased 

 to act, as the stroke of a bat on a cricket- 

 ball. Were there no opposing force, as 

 gravity, the motion of such a body would 

 be uniform. 



2. Retarded motion is produced by 

 some force acting on a body in a direc- 

 tion opposed to that which first put it in 

 motion, and thus gradually diminishing 

 its velocity. 



3. Accelerated motion is produced when 

 the force which puts a body in motion 

 continues to act upon it during its mo- 

 tion, so that its velocity is continually 

 increased. 



4. In cases of accelerated and of re- 

 tarded velocity, a distinction is observed 

 between the initial and the final velocity 

 of a body : the former is exhibited by 

 the body when it commences its motion ; 

 the latter only after the lapse of a certain 

 time : both are measured by the space 

 which the body would have passed over, 

 in one second, with the uniform initial or 

 final velocity, as the case may be. 



5. Reflected motion is produced when 

 a body is turned out of a straight line by 

 some force independent of gravity ; it is 

 the result of re-action being contrary to 

 action. If a ball be thrown against a 

 wall, it rebounds, in consequence of the 

 re-action of the wall against which it is 

 struck, and it is said to have reflected 

 motion. 



6. Simple motion is that which results 

 from the operation of a single force. But 

 when two or more forces act in different 

 directions on the same body, at the same 

 time, the motion so produced is called 

 compound; and the single force which 

 represents the combined effects of all the 

 forces, is called the resultant. 



7. Circular motion is the motion of a 

 body in a ring, or circle, and is produced 

 by the action of two forces. By one of 

 these forces the moving body tends to 

 fly off in a straight line, while by the 

 other, it is drawn towards the centre, and 

 thus it is made to revolve, or move round 

 in a circle. The force by which a body 

 tends to go off in a straight line is called 

 the centrifugal force; that which draws 



226 



it towards the centre, is called the oert' 

 tripetal force. 



8. In curvilinear motion the direction 

 of the body is neither straight forward 

 nor diagonal, but through a line which is 

 curved. This kind of motion may be in 

 any direction ; but when it is produced 

 in part by gravity, its direction is always 

 towards the earth. A stream of water 

 from an aperture in the side of a vessel, 

 as it falls towards the ground, is an ex- 

 ample of a curved line ; and a body pass- 

 ing through such a line, is said to have 

 curvilinear motion. 



9. It may happen that an object is in 

 motion, as well as the spectator, in which 

 case, the motion of the latter is trans- 

 ferred to the former, and the whole mo- 

 tion of the object, compounded of that 

 which it has of its own, and that which 

 it appears to have from the motion of the 

 spectator, is called the apparent or rela- 

 tive motion. 



MOTION, CENTRE OF. That point 

 which remains at rest, while all the other 

 parts of a body move about it. 



MOUNTAIN. A considerable eleva- 

 tion of the surface of the earth, attaining 

 a height of more than two thousand feet. 

 A chain of mountains is, strictly speak- 

 ing, a series of which the bases are con- 

 tinuous. A hill is merely a small moun- 

 tain, and the lowest elevations of this 

 kind are called hillocks or mounds. A 

 mountain of a conical form, with the 

 summit narrow, is named a cone; when 

 of the same form, but more massy, and 

 with the summit depressed and rounded, 

 it is a dome; these are of volcanic origin. 

 See Platform and Peak. 



MOUNTAIN BLUE. Blue copper, or 

 carbonate of copper, the more remark- 

 able varieties of which are those from 

 Chessy, and from the Bannat, combined 

 with various substances. Mountain green 

 is the common copper green, also a car- 

 bonate. 



MOUNTAIN CORK. The elastic 

 variety of asbestos. Mountain leather 

 is the tough variety. When it occurs in 

 very thin pieces, it is called mountain 

 paper. The ligniform variety is named 

 mountain or rock wood. 



MOUNTAIN LIMESTONE. Carbo- 

 niferous limestone. A series of limestone 

 strata of marine origin, usually forming 

 the lowest member of the coal measures. 



MOUNTAIN SOAP. A mineral sub- 

 stance found in the island of Skye, and 

 employed in crayon painting. 



MOUNTAIN TALLOW. A curious 



