MOTION 



;is tin- law of in. -i tin, nince it assert* 



i body can niter its state o( 



rest or motion without outside in- 



tliicnrr ; in other words, every 



lias inertia. The law also 



;i definition of force, since 



ui- m;iy say that force is that which 



'<> produce change of motion 



in a body on which it acts. It also 



i'iw a body will move when 



not acted upon by external forces 



always in a straight line. 



The second law states how the 

 change of motion depends on the 

 magnitude and direction of the 

 force. By motion Newton meant 

 iin.iin iiMiin ; and, in the same way, 

 his impressed force includes the 

 idea of time, for the change of 

 momentum will depend on the 

 time during which the force is act- 

 ing, as well as on the magnitude of 

 the forces. It must be noted that 

 it is the change in momentum which 

 is proportional to the impulse of 

 the force ; therefore it does not 

 matter whether the body on which 

 the force acts is originally at rest 

 or in motion. The law gives a 

 means of defining and measuring 

 forces as well as masses. If a num- 

 ber of forces act in succession on the 

 same mass, the changes produced 

 in velocity will be proportional to 

 the forces. Their relative magni- 

 tudes are measurable therefore in 

 terms of the velocities they produce. 



The third law states that all 

 forces are of the nature of a stress 

 between portions of matter, since 

 every force must necessarily be 

 accompanied by an equal and 

 oppositely directed reaction. See 

 Dynamics; Energy. 



Motion. In music, the progres- 

 sion of voices or parts from note to 

 note. The motion of a single part 

 may be upward ; downward ; con- 

 junct, proceeding by single degrees ; 

 disjunct, proceeding by skips. 

 Comparing one part with another, 

 motion may be of three kinds : simi- 

 lar, when the parts move in the 

 same direction; contrary, when 

 they move in opposite directions ; 

 oblique, when one is stationary 

 while another moves up or down. 



Motive (L. \At. motivum, from 

 movere to move). Process of will 

 which moves or excites a person to 

 make a certain decision or choice. 

 In the widest sense as a psychologi- 

 cal term, motive is used for all the 

 internal influences which assert 

 themselves in a particular case as 

 incentives to the will ; in a nar- 

 rower sense, it is only the ideas of 

 the objects and possible effects of 

 our action which are existent in 

 consciousness, when the choice be- 

 tween several possible acts of will 

 takes place. The term is also used 

 in art, literature, and music in the 

 sense of a leading subject or theme. 



5553 



Motley, JOHN LOTHBOP (1814- 

 77). American hUtorian. Horn at 

 Dorchester, MJWS. . April 15. 1814 

 he was edu 

 o a t e d at 

 Harvard, Gat- 

 tin g e n, and 

 Berlin. For a 

 short time he 

 was a member 

 of the Ameri- 

 can legation 

 in St. Peters- 

 burg; from 

 1861-67 was 



y I American 



/ minister i n 



Vienna, and from 1869-70 in I/on- 

 don. He passed much time in Eng- 

 land, and it was at Frampton Court, 

 Dorchester, Dorset, that he died, 

 May 29, 1877. One of his daughters 

 married Sir William Hareourt. 



Motley began his literary career 

 with a novel, Morton's Hope, fol- 

 lowed by articles in The North 

 American Review, and by another 

 novel, Merry Mount, 1849. He had 

 already formed the idea of writing 

 the history of the Dutch, and he 

 spent some time in Holland, Bel- 

 gium, and Germany studying the 

 authorities. In 1856 his Rise of 

 the Dutch Republic appeared in 

 London in three volumes, and at 

 once made him famous. It was 

 translated in to French, German, and 

 Dutch, and was followed by the 

 History of the United Netherlands, 

 1860-68, another great success. 



Motley writes with real enthu- 

 siasm about the struggles of the 

 Dutch for freedom, but the books 

 are far removed from partisan writ- 

 ings, although later research has 

 caused some of his judgements to 

 be modified. His style is clear and 

 vigorous, rising occasionally into 

 passages of noble prose. He wrote 

 also the Life and Death of John of 

 Barneveld, 1874, a continuation of 

 his earlier book, but hardly so suc- 

 cessful. His correspondence was 

 edited by G. W. Curtis, 1889. 

 See Memoir, O. W. Holmes, 

 1898; J. L. Motley and His 

 Family, Further Records and 

 Letters, ed. S. St. J. Mildmay. 

 1910. 



Motor. Word 

 used in a num- 

 ber of senses. In 

 machinery, a 

 motor is a prime 

 mover, e.g. a 

 steam engine, an 

 electric motor, an 

 internal combus- 

 tion engine, etc. 

 In the latter con- 

 nexion it is often 

 used as an ad- 

 jective, as motor 

 car. In mathe- 



MOTOR 



matics, motor a a term for a 

 quantity indicating the size, direc- 

 tion, position, and pitch of a screw. 

 In anatomy and physiology, the 

 word is used as designating or per- 

 taining to particular nerve fibres 



An electric motor is a type of elec- 

 tric machine. The modern electric 

 motor is an inverted dynamo, 

 though historically the motor in 

 older than the latter. Faraday 

 appears to have been the first to 

 produce rotary motion by means of 

 electro-magnetic currents. 



The first motor to operate on a 

 practical scale was constructed by 

 Jacobi of St. Petersburg, in 1834. 

 It was actuated by a battery of 

 64 Grove cells, and propelled a boat 

 on the river Neva at over two m. an 

 hour. So long, however, as the im- 

 mediate source of the energy was 

 represented by the consumption 

 of zinc in an electric battery, the 

 electric motor had no possible 

 chance as compared with steam- 

 driven appliances ; and it required 

 the development of the dynamo to 

 make the electric motor a machine 

 for practical use. The relation 

 of an electric motor to a dynamo 

 is shown in the appended diagram. 

 The armature A of the dynamo is 

 driven by some other agent steam, 

 oil, or gas engine, water wheel or 

 turbine ; the current developed 

 is carried to the field magnets B 

 of the motor ; these in turn compel 

 the armature, C, of the motor to 

 rotate. The axle of the motor may 

 be connected directly or indirectly 

 to the machine which is to be 

 driven, which may be the toy-like 

 drill of the dentist or the propeller 

 of an ocean liner. 



Electric motors are of two 

 general classes, those using direct 

 current and those using alternating 

 current ; while they are also dis- 

 tinguished as shunt wound, series 

 wound, and compound wound , 

 single-phase, two-phase, and three- 

 phase : open, partly enclosed, and 



D E 



Motor. Diagram illustrating principle of a dynamo, D, 

 whose armature. A, is driven by steam engine or other 

 prime mover. The dynamo actuates motor, E. by means 

 of magnets, B, and armature, C, driving line shaft, F, 

 from which power is distributed in various directions 



M 7 



