104 
MIGRATION AND FLIGHT. 
rior to human skill; for it is affirmed, that vessels 
which have lost their latitude in hazy weather, have 
steered entirely by the noise of the Turtles in swim- 
ming. The object of their voyage, as in the case of 
birds, is for the purpose of laying their eggs on a 
spot peculiarly favourable. 
It is, indeed, this instinctive power and stimulus 
which is the real point to excite our astonishment in 
the migration of birds; for when we take into con- 
sideration what has been said of their rapid flight, 
which would enable an Eagle, in nine days, allowing 
him sixteen or seventeen hours for repose, to go round 
the world, there is nothing so very extraordinary 
in the journey of a Swallow from the shores of 
England to those of Sierra Leone in Africa; where 
a person, who resided there for seven years, con- 
stantly observed our three species, many of them 
remaining all the year, hut their numbers much 
diminished from spring to autumn, when they were 
supposed to he absent spending their summer in 
Europe. 
On looking at the map, it will be seen, that with- 
out further peril by sea, than simply crossing The 
short space of the British Channel and Straits of 
Gibraltar, (either of which, at their narrowest parts, 
even a barn-fed Sparrow might easily do in an hour 
or two,) a bird might make almost a direct course to 
Sierra Leone, a distance of about 3000 miles, which 
space a Swallow would, without effort, traverse in 
three days, including time for roosting at night, and 
which even the Sparrow could perform at leisure, 
and without the least fatigue, in less than a fortnight. 
The above calculation is made on the supposition 
