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GENERAL SCIENCE 



FIG. 198. Here we see the officers of a submarine studying the picture of what 

 is happening above, which the periscope has reflected upon the table 

 somewhat in the same way as a picture is thrown upon the sheet by a 

 reflectoscope. Courtesy Child's Book of Knowledge. 



FIG. 199. These men are taking a last look round before sinking. Air-compressors 

 maintain the supply of air in a submarine. Formerly, white mice used to be 

 kept on board to indicate, when they fainted, that the air was getting foul. 



Courtesy Child's Book of Knowledge. . 



