382 NATURE'S TEACHINGS. 



spiral, and the object viewed in a slanting direction, it would 

 be almost impossible to distinguish between the ring and the 

 spiral. 



Among the most remarkable of these examples are the two 

 right-hand figures. That on the extreme right represents a 

 spiral vessel taken from the so-called root, or " rhizome/ ' of the 

 "Water-lily, and the other is a similar vessel taken from a 

 branch of the Yew-tree. It has been suggested that to this 

 spiral structure is due the proverbial elasticity of the yew-tree, 

 which has from time immemorial rendered it the best wood for 

 the manufacture of bows. 



Diving and Divers. 



It has already been mentioned that the flexible tubes used by 

 modern divers are constructed on the model of several structures 

 belonging to the animal and vegetable kingdoms. 



We will now see how they are utilised. 



In the earlier stages of the divert art the Diving-bell 

 afforded the only means of gaining access to the bed of the sea, 

 even in comparatively shallow waters. The mode in which 

 this result was obtained was simple enough, and though it 

 carried with it the germs of still greater improvements, was 

 but limited and uncertain in its action. 



The reader is probably aware that if a vessel be filled with 

 air, no liquid can obtain admittance until a corresponding 

 amount of air be set free. Suppose, for example, that an empty 

 tumbler be inserted over a basin of very clean water, and 

 pressed downwards, it will be found that scarcely any water 

 will enter it, the air having taken up all the available space, 

 and only allowing as much space as may be accounted for by its 

 faculty of compression. 



It is evident, therefore, that if an enlarged tumbler could be 

 lowered to the bed of the sea, a man might be enclosed within 

 it, and for a time be able to support life by means of the air 

 contained within the "bell," as this enlarged tumbler was 

 popularly called. 



It is equally evident that within a short time the air within 

 the bell must be exhausted, and that, unless a fresh supply 



