61 



the influence of the slightest signs of an approaching change of 

 weather long before anything of the impending change is perceived 

 on the earth's surface, where the earliest indications of it are 

 probably not felt until about twenty-four hours later." He further 

 remarks " It can hardly be doubted that all changes of weather 

 have their origin in the higher strata of the atmosphere" (page 

 78). If birds have twenty-four hours' notice of a storm before 

 its approach is detected on the earth, through flying at great alti- 

 tudes, it is difficult to imagine why, considering the high rate of 

 speed at which they are supposed to migrate, that they do not 

 put forth their powers and convey themselves to a place of safety 

 without breaking their flight at all, or descending near to the 

 surface of the earth. In the light of this enquiry it will be 

 interesting to examine the behaviour of migrating birds on the 

 approach of one of these disturbances of the atmosphere as 

 described on pages 78-79. 



After remarking on the familiar phenomena of the various 

 layers of cloud travelling towards different points of the horizon, 

 the author formulates the theory from a study of these move- 

 ments, that the appearance of light fleecy clouds at great heights, 

 traversing the heavens in an opposite direction to that of the 

 wind at the surface of the earth, predicates a change of the latter 

 to an opposite quarter. And as birds, according to his theories, 

 travel at these great heights during the normal performance of 

 their migratory flights, they would naturally become aware, or 

 actually meet with the adverse wind or conditions, " long before 

 anything of the impending change is perceived on the earth's 

 surface." At a time, however, when the winds at the lowest 

 elevations are light south-east, birds travel at only very moderate 

 heights, it must be supposed because conditions above are un- 

 favourable to so-called normal migration. It is difficult to see, 

 therefore, how, whilst they are flying low, they can become 

 acquainted with the first indications of the coming change, if 

 they are only at that particular period exhibited at the great 

 elevations before described ; for it is not until the west or south- 

 west wind gains the ascendancy at the surface of the earth 

 or in other words, that the coming change has taken place 

 we are told, that the migration passes into higher altitudes, its 

 speed being at the same time strikingly accelerated. 





