46 NATURE'S TEACHINGS. 



its spicules against the sides of its tube, and in shortening 

 itself and withdrawing the spicnles ready for another push. 



ANOTHER needful accessory of vessels now comes before us, 

 namely, the capability of forming rafts or life-belts, which will 

 float under any circumstances. Here, again, every human 

 invention of which I know has been anticipated by Nature. 

 Take, for example, the familiar instance of the cork life- belt 

 and the cork edgings of the life-boat. Both are constructed 

 on the same principle, i.e. the maintenance of cells which are 

 filled by air instead of water, and are impervious to the latter. 



The material most used for this purpose is cork, and life- 

 belts constructed of it have long been in well-deserved use, the 

 cork-bark having the property of holding much air and ex- 

 cluding water. Many of our life-boats are furnished with a 

 broad and thick streak of cork, so that even if the boat be 

 filled with water and upset, she will right herself and swim. 

 I regret to say that many of the so-called " life-belts " which 

 are offered for sale ought rather to be called " death- belts/' 

 they having been found to be filled with hay and straw, with 

 only a few shavings of cork just under the covering of the belt. 



Indeed, so buoyant is this substance that a very efficient belt 

 can be made by stringing together three or four rows of ordinary 

 wine corks, and tying them round the neck like a collar. Under 

 these circumstances it is simply impossible to sink, and though 

 any one may collapse from exhaustion, drowning is almost out 

 of the question. The now well-known cork mattress, which is 

 used in many ships, is another example of the same principle. 



Lately there has been invented a " life-collar," which 

 possesses similar advantages, but occupies less space when not 

 wanted. It is nothing more than a tube of caoutchouc, which 

 can be inflated at pleasure, and tied round the neck. The 

 ordinary life-belt goes round the waist, and^ needs much more 

 material without obtaining a better result, which is simply the 

 keeping of the mouth and nostrils out of the water. 



Perhaps the most buoyant of living beings is the Portuguese 

 Man-of-war (Physalis pelagicus), which floats on the surface of 

 the ocean like a bubble. It can at pleasure distend itself with 

 air and float, or discharge the air and sink. 



Now, there is a very remarkable swimming dress, which. 



