SPIRAL SPRINGS. 



367 



be lound in young children. Before they are old enough to 

 take care of themselves they are perpetually falling down, and 

 never hurting themselves. I have seen a little girl of five 

 years old roll from top to bottom of a lofty staircase. It looked 

 as if the child must be killed, but she was only giddy with her 

 many revolutions, and a little bruised about the elbows. The 

 reason of this curious immunity from injury is, that the bones, 

 especially those of the skull, are not completely united, and so 

 act on the principle of the compound spring. 



THE SPIRAL SPRING. 



THIS subject is so large, and there are so many examples, 

 both in Art and Nature, that it is not very easy to make selec- 

 tions which will sufficiently answer the purpose. 



WATER-LILY. L 



POISON-CELL OF HELIANTHOID. 



ANTHEROZOIDS. 



SPIRAL SPRING. BED SPRING. 



WATCH SPRING 



The upper left-hand figure of the illustration represents the 

 ordinary Spiral Spring made of wire, and used for its power of 

 resuming its shape when compressed. In early childhood most 

 boys have had practical experience of this spring in the toy 

 guns and cannons with which they are supplied. The spring 

 is compressed by the ramrod, and held in its place by a catch. 

 If a pellet be placed in the gun, and the catch released by 

 pulling the trigger, the spring flies back to its former shape, 

 and drives the pellet. 



An exactly similar spring is used in the well-known "Needle- 



