USEFUL AETS. 



CHAPTER IV. 



THE STOPPER, OR CORK.— THE FILTER. 



Vessels and their Covers. — Corks. — Mode of bottling Wine. — Conical Corks and 

 Stoppers. — Self -fitting Candles. — Candle -fixers. — The Vent-peg. — The 

 Blow-guns and their Missiles. — The Serpula and its Conical Stopper. — The 

 Filter. — The Bosjesman procuring Water. — How to make a simple Filter. — 

 The Earth as a Filter. — The Sea-mouse, or Aphrodite, and its filtering Appa- 

 ratus. — The Duck's Beak, and its beautiful Structure. — The Jaw of the 

 Greenland Whale. — Fork-grinder's Respirator. — How Insects breathe. — 

 Spiracles, and their general Structure. — Spiracle of the Fly. — Experiment 

 upon a Cockroach, and its Result. 



The Stopper, or Cork. 



THIS object, as depicted in the illustration, is a product of 

 civilised life, though, as soon as a savage could make a 

 vessel, he seems to have made a Cover for it if it were of large 

 diameter, or a Stopper if the opening were small. Even the 

 very Bosjesman, who is quite unable to make a clay vessel, and 

 uses empty ostrich eggs by way of water-bottles, is yet 

 capable of making plugs with which he can stop up the 

 apertures. Then the Kafir, with his gourd vessels, whether 

 they be for water or snuff, makes a plug that fits tightly 

 enough to exclude the air, as well as to retain the contents. 



The invention of glass bottles necessarily brought with it the 

 introduction of a new kind of plug, and a material for such a 

 plug was found in the bark of the cork-tree, a species of oak. 

 This bark possesses the capability of compression to a very 

 great extent, and, being highly elastic, it expands as soon as 

 the pressure is removed. 



Thus, in bottling wine, the corks are always made much 

 too large to go into the mouths of the bottles. They are first 



