MIGRATIONS AT GREAT ALTITUDES. 383 



concourse of people was assembled, a heavy thunder 

 shower broke over them. We pointed out the ap- 

 proaching storm, but people would not move; and the 

 destruction of ladies' dresses on that morning, by the 

 subsequent downpour, must have represented some- 

 thing very large : some thousands of handsome dresses, 

 etc. must have been entirely ruined. Yet nothing 

 would have been easier than to get away in time 

 to have avoided all this; it was too late when the 

 first drops began to fall, and the general stampede 

 took place. 



The object of these observations is to lay stress upon 

 the necessity for trained observation of the phenomena 

 of the atmosphere : the paucity of accurate detail obtain- 

 able about the question of the migratory flight of birds, 

 affords a good instance in point. Most of them pass 

 unnoticed and unseen. How many people can say 

 that they have witnessed these wonderful flights ? There 

 are several reasons for this. The flight of many migrants 

 is conducted at such great elevations, that they are 

 only imperfectly visible from the earth beneath ; others 

 no doubt actually do pass beyond the range of human 

 vision : we can have no hesitation in asserting that this 

 is so, especially in the case of small birds.* Many 

 migrations also occur during the night, when it is only 

 the distant notes of birds, passing high in the zenith, 

 heard at intervals in the prevailing stillness, that dis- 



* Many reasons have been quoted to account for the great heights 

 at which the migration flights of birds are often conducted : Person- 

 ally we believe that the atmosphere at these altitudes is found to be 

 much calmer than nearer the earth's surface, and the migrants thus 

 pass above the reach of storms which are so liable to occur at lower 

 levels. During heavy gales the cirrus clouds at great altitudes are for 

 instance, often to be seen floating apparently motionless, when the lower 

 strata of cumulous clouds are passing with great velocity beneath. 



