258 LIGHT SCIENCE FOR LEISURE HOURS. 



drawn for different vertical elevations, the resulting 

 shading will be dark or light, according as the slope 

 is steep or gentle. This method of shading affords 

 scope as well for surveying skill as for draftsmanship. 

 (From Once a Week, May 1, 1869.) 



A SHIP ATTACKED BY A SWORD-FISH. 



WE have always been puzzled to imagine how the 

 ' nine-and-twenty knights of fame, 7 described in the 

 ( Lay of the Last Minstrel,' managed to ' drink the red 

 wine through the helmet barr'd.' But in nature we 

 meet with animals who seem almost as inconveniently 

 armed as those chosen knights, who 



. . . quitted not their armour bright, 

 Neither by day, nor yet by night. 



Amongst such animals the sword-fish must be recog- 

 nised as one of the most uncomfortably armed creatures 

 in existence. The shark has to turn on his back 

 before he can eat, and the attitude scarcely seems sug- 

 gestive of a comfortable meal. But the sword-fish can 

 hardly even by that arrangement get his awkwardly 

 projecting snout out of the way. Yet doubtless this 

 feature, which seems so inconvenient, is of great value 

 to Xiphias. In some way as yet unknown it enables 

 him to get his living. Whether he first kills some one 

 of his neighbours with this instrument, and then eats 

 him at his leisure, or whether he plunges it deep into 



