124 COMBUSTION OF MAGNESIUM. 



CHAPTER XIV. 



COMBUSTION OF MAGNESIUM. 



ONE day, just before the time for dinner, John came 

 home from a ramble which he had been taking through 

 the streets in London. The table was set for dinner, and 

 Lawrence was reading a newspaper, having comfortably 

 established himself in a large arm-chair near a window. 



When Lawrence heard the rap which John gave at the 

 knocker at the door, he said, 



" There comes John." 



He knew him by his rap. 



It is surprising how many different modes there are in 

 use among mankind for communicating ideas and intelli- 

 gence as substitutes for language. One very striking in- 

 stance is that of the boatswain's pipe, on board ships at 

 sea, which interested John very much on his voyage across 

 the Atlantic in the steamer. The boatswain, as perhaps 

 the reader knows, is the officer on board a ship who has 

 charge of the sails and rigging; and as the winds and 

 waves are often so boisterous that no human voice could 

 be heard at the distance at which commands often have to 

 be given, the custom has grown up among all European 

 nations of the boatswain's giving his directions to the men 

 by means of a peculiar kind of whistle, called the boat- 

 swain's pipe, which makes a very shrill and piercing sound, 

 not loud, but so penetrating that it can be heard in the 

 stormiest times above, or, rather, through the sound of the 

 heaviest roaring and thundering of the winds and waves. 



John had been quite surprised dui'ing the voyage at two 



