MOTION. 



411 



Fig. 214. 



moving them. There are no examples of the 

 compound pulley in animal structures. 



We recognise the simple pulley in the trans- 

 mission of the tendons of the peronei muscles 

 through the groove of the external malleolus of 

 the human ankle-joint, in the tendon of the obtu- 

 rator internus gliding through the groove in the 

 os ischii, in the tendon of the circumflexus 

 palati passing through the hamular process of 

 the sphenoid bone, in the tendon of the obliquus 

 superior gliding through the ring attached to 

 the frontal bone, and in several other instances 

 where a change of the directions of the limbs 

 results from tendons passing over joints, through 

 grooves in bones, or under ligaments, by which 

 the muscles are capable of producing effects 

 on distant organs without disturbing the sym- 

 metry of the body, an effect which, owing to 

 the limited power of contraction in the muscles, 

 could be accomplished in no other way. 



Of uniform motion. If a body move 

 constantly in the same manner, or if it pass 

 over equal spaces in equal periods of time, its 

 motion is uniform. The velocity of a body 

 moving uniformly is measured by the space 

 through which it passes in a given time.* 



The velocities generated or impressed on 

 different masses by the same force are reci- 

 procally as the masses.")- 



Motion uniformly varied. When the mo- 

 tion of a body is uniformly accelerated, the 

 space it passes through during any time what- 

 ever is proportional io the square of the time. 



In the leaping, jumping, or springing, of 

 animals in any direction, (except the vertical,) 

 the paths they describe in their transit from one 

 point to another in the plane of motion are pa- 

 rabolic curves. 



The legs move by the force of gravity as a 



* Thus if v be the space passed over by the body 

 in an unit of time, that space X by t, or t v will 

 be the space s passes over in t units, that is, 

 s = tv (1). 



t If a force communicates a velocity v to a 

 mass m, and a velocity v' to a mass m', then we 



have mv = m v' (2). 



Generally, if/be the accelerating force, the space 



=/<*, (3). 



and s= '-!L' (4). 



pendulum. To the many instances already 

 recognised of the connexions subsisting be- 

 tween the functions of living animals and the 

 physical sciences, another remarkable con- 

 tribution has been recently added by the Pro- 

 fessors Weber, whose experimental researches 

 satisfactorily demonstrate that the swinging 

 forwards of the legs of animals in progres- 

 sive motion obeys the same laws as those 

 of the periodic oscillations of the pendu- 

 lum. In order to ascertain these relations, 

 MM. Weber instituted a series of experi- 

 ments upon legs of given lengths, both 

 in the living and dead subject, and under 

 variously modified circumstances. Having 

 removed a leg from the trunk at the hip- 

 joint, and suspended it by a short thread 

 that it might move as if upon the axis of the 

 head of the femur; upon giving it an im- 

 pulse they found it oscillated nearly in the 

 same time as in the living state. They next 

 communicated a vibratory motion to a leg sus- 

 pended to the acetabulum by the ligaments of 

 the hip-joint only, the muscles having been 

 previously cut through : in this experiment the 

 oscillatory movements were rather less than in 

 the preceding. The oscillations of the leg 

 of a dead person after the rigidity of the muscles 

 had subsided, were still further diminished. 

 On comparing the durations of the vibrations 

 of the legs in these several states with those of 

 the living, they found their periods nearly equal 

 or in the following proportions. 



* A metre = 3.2808992 feet. 

 A millimetre 0.031W7 inch. 



