316 THE HARMONIES OF NATURE. 



them, with the plenty and the mild temperature they require 

 for the rearing of their progeny. 



While numerous birds leave us in autumn, others, which 

 have brought forth their young in the Arctic regions, seek our 

 shores at that season of the year, or pass over our heads on 

 their way to more southern lands : for the icebound lakes, 

 the frozen rivers, the deserted channels, and the snowclad 

 shores of the hyperborean zone are no longer able to afford 

 them any nourishment, and in spite of their thick downy 

 mantle, a temperature which converts mercury into a solid 

 body may render a change desirable. But as the days again 

 lengthen, and the sun, rising higher and higher in the heavens, 

 dissolves the iron bonds of winter, the dispersed legions of 

 ducks, geese, swans, strand and sea-birds advance once more 

 from the south to feast upon the abundance of the softened 

 earth or of the prolific waters, and to rear their young under 

 the grateful influence of a continuous day. 



Thus the living tide ebbs and flows in everlasting succession, 

 and as the floods of the ocean obey the behests of distant 

 celestial bodies, thus also the migrations of the birds are ruled 

 by immutable and eternal laws ! 



