MIGRATION AND FLIGHT. 85 



with as much certainty as the sailor steers his ship across the 

 wide ocean by his skill and navigation, and that mysterious 

 needle ever pointing to the north. Neither is this instinct 

 confined to birds ; it has been observed in turtles, which cross 

 the ocean, from the Bay of Honduras to the Cayman Isles, 

 near Jamaica, a distance of 450 miles, without the aid of 

 chart or compass, and with an accuracy superior to human 

 skill; for it is affirmed, that vessels which have lost their 

 reckoning in hazy weather, have steered entirely by the noise 

 of the turtles in swimming. 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 consideration 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, constantly observed our three species, many 

 of them remaining all the year, but their numbers much 

 diminished from spring to autumn, when they were supposed 

 to be absent, spending their summer in Europe. 



On looking at the map, it will be seen that without 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 a Sparrow could perform at 

 leisure, and without the least fatigue, in less than a fortnight. 

 The above calculation is made on the supposition that the airy 

 travellers keep over the land as much as possible ; but if the 

 straightest course were preferred, they might, by crossing the 

 Bay of Biscay, perform it in less time. And that Swallows do, 



