NATURAL HISTORY. 



291 



" Such murmur fill'd 



Th' assembly, as when hollow rock? retain 



The sound of blustering winds, which all night long 



Had rous'd the sea." MILTON. 



939. There are few persons who have crossed the Atlantic that have not 

 observed these wanderers of the deep skimming along the surface of the wild and 



wasteful ocean ; flitting past the 

 vessel like swallows, or following in 

 her wake, gleaning their scanty 

 pittance of food from the rough and 

 whirling surges. Habited in mourn- 

 ing, and making their appearance 

 generally in greater numbers previous 

 to, or during a storm, they have 

 long been regarded by the ignorant 

 and superstitious, not only as the 

 foreboding messengers of tempests 

 and dangers to the hapless mariner, but as wicked agents, connected somehow or 

 other in creating them. " Nobody," they say, " can tell anything of where they 

 come from, or how they breed, though (as sailors sometimes say) it is supposed that 

 they hatch their eggs under their wings as they sit on the water." This mysterious 

 uncertainty of their origin, and the circumstances above recited, have doubtless 

 given rise to the opinion so prevalent among seafaring men, that they are in 

 some way or other connected with supernatural powers in the air. In every 

 country where they arc known, their names have borne some affinity to this belief. 

 They have been called witches, stormy petrels, the devil's birds, and Mother Gary's 

 chickens, probably from some celebrated hag of that name ; and their unexpected 

 and numerous appearance has frequently thrown a momentary damp on the 

 mind of the hardiest seaman. 



940. Why are sea-birds enabled to breast the waves in 

 tempestuous weather ? 



Because the waves, instead of rolling with the velocity of the 

 wind (as is commonly imagined), roll very little. When we look 

 at them from the shore and with a side wind, they seem to roll 

 on, and they always appear to move slower in a fresh breeze. 

 They heave and sink, the times being as the square roots of their 

 lengths, so that, if a wave four feet broad changes from ridge 

 to trough in four seconds, one of sixteen feet will change in eight 

 seconds. Now, as the apparent forward motion is half the width, 

 the four-feet wave will appear to move at the rate of rather 

 less than a mile and a half in the hour, the sixteen-feet 

 wave at rather less three-quarters of a mile in the hour, which is 

 very slow motion. 



