THE RETURN OF THE BIRDS 75 



both as regards space and time. We shall discuss some of 

 the many uncertainties and some of the difficult problems 

 of migration in subsequent studies. Meanwhile, let us 

 keep the broad facts clear, and realise the wonder of them. 

 " Any one," Gatke says, " who on dark, starless Autumn 

 nights has heard the babel of voices of these hundreds of 

 thousands and even millions of birds travelling past him 

 overhead, in one fixed direction and in undiminishing 

 numbers for the space of whole months, without the help of 

 any guiding mark discernible by human eye, cannot fail 

 to be led, by the supreme grandeur of this phenomenon, to 

 speculate as to what kind of capacities the unfailing per- 

 formance of such an act is due ; more especially, if like 

 myself he has for more than half a century watched the 

 phenomenon recurring regularly at each solstice with the 

 same unerring precision as the planets in their courses." 



