MOTION AND LOCOMOTION. 145- 



just more than half a kilogram would lift it; but for every 

 centimeter through which P descended, W would only be 

 lifted half a centimeter. On the other hand when the 

 weight-arm in a lever is longer than the power-arm, there 

 is loss in force but a gain in the distance through which 

 the weight is moved. 



Examples of the first form of lever are not numerous in 

 the Human Body. One is afforded in the nodding move- 

 ments of the head, the fulcrum being the articulations 

 between the skull and the atlas. When the chin is elevated 

 the power is applied to the skull, behind the fulcrum, by 

 small muscles passing from the vertebral column to the 

 occiput; the resistance is the excess in the weight of the 

 part of the head in front of the fulcrum over that behind 

 it, and is not great. To depress the chin as in nodding 

 does not necessarily call for any muscular effort, as the 

 head will fall forward of itself if the muscles keeping it 

 erect cease to work, as those of us who have fallen asleep 

 during a dull discourse on a hot day have learnt. If the chin 

 however be depressed forcibly, as in the athletic feat of 

 suspending one's self by the chin, the muscles passing from 

 the chest to the skull in front of the atlanto-occipital artic- 

 ulation are called into play. Another example of the em- 

 ployment of the first form of lever in the Body is afforded 

 by the curtsey with which a lady salutes another. In 

 curtseying the trunk is bent forward at the hip-joints, 

 which form the fulcrum; the weight is that of the trunk 

 acting as if all concentrated at its centre of gravity, which 

 lies a little above the sacrum and behind the hip-joints; 

 and the power is afforded by muscles passing from the thighs 

 to the front of the pelvis. 



Levers of the Second Order. In this form the weight 

 or resistance is between the power and the fulcrum. The 

 power-arm PF is always longer than the Weight-arm WF, 

 and so a comparatively weak force can overcome a consid- 

 erable resistance. But it is disadvantageous so far as re- 

 gards rapidity and extent of movement, for it is obvious 

 that when P is raised a certain distance JFwill be moved a less 

 distance in the same time. As an example of the employ- 



