ANNIVERSARY ADDRESS 193 



diverse, and that much has been written upon the subject 

 by various authors, of whom certain have undertaken to 

 determine with more or less exactitude the precise 

 directions that the flocks should follow. A greater mass 

 of information must, however, be accumulated before we 

 are enabled to accept any generalizations of this des- 

 cription, and we must be content for the present to 

 indicate certain definite courses which birds seem to 

 follow to the comparative exclusion of others, leaving it 

 for future generations to continue the work which we 

 have begun. Here let us take a glance at what has 

 been done in Britain. Through the instrumentality of 

 the British Association a Committee was formed to collect 

 observations upon birds at the various lighthouses and 

 light-ships around our coasts, observations which were 

 continued from 1880 to 1887 inclusive. From the 

 information thus gained we might consider ourselves 

 justified in laying down certain rules which govern the 

 immigration and emigration of birds as regards our 

 shores, and this may no doubt be done to a considerable 

 extent without serious error; but we must not fail to 

 take into full account the exceptionally favourable and 

 convenient position of our lights, the paucity of observers, 

 and the fact that other stations might afford equally 

 valuable, or even contradictory, results if equal diligence 

 was used for a similar length of time.* 



There is, moreover, the question of the height at which 

 bii-ds fly, and consequently what proportion of them fail 

 altogether to be observed owing to their altitude; whether 

 in fact we only notice those forced down from above by 

 such causes as adverse weather. And in this connection 

 it may be mentioned that birds have been noticed crossing 

 the field of a telescope directed towards the sun or the 

 moon at an estimated heiofht of from 1500 — 15,000 feet. 



* Similar observations have been carried on, and ar^ still being 

 carried on, at the Danish light-stations, 

 Z 



