xiv INTRODUCTION. 



when a gull flying seawards meets just over the cliff'-edge 

 a strong up-cun-ent, and sails most triumphantly upwards 

 and onwards. We need not go into the question further, 

 for our pui-pose is simply to point out that it is not 

 difficult to watch sailing Crows and sailing Gulls with a 

 field-glass, that they seem to describe circles or ellipses 

 without detectable wing-strokes, and that this is one of 

 the many unsolved problems of flight. The way of the 

 Eagle in the air is still too hard for us, and if it be 

 shown that the wonder was made by misobsei'vation more 

 wonderful than it really is, there is the gain of removing 

 a common sight from the category of the obscure and 

 marvellous to the category of the intelligible and wonderful. 



Study of Behaviour. 



The study of behaviour is in many ways the most 

 attractive of all, but at the same time one of the most 

 diffictilt. We refer not to the difficulties of precise obser- 

 vation and faithful recording of what takes place, but to 

 the difficulty of avoiding a mixture of inference with 

 observation, and to the difficulty of drawing the connect 

 inference when the observations are complete. One observer 

 is too generous, reading his own intelligence into the bird ; 

 another is too niggardly, reducing the bird to the level 

 of an automatic machine. The recent developments of 

 photography have made it possible to have, for instance, 

 a complete cinematographic record of a bird's behaviour 

 in feeding its young ; but the difficulty is to get mentally 

 near enough to the bird to understand how much it under- 

 stands. One of the sure ways of attacking the problem is 

 that which has been followed with conspicuous success by 

 Professor Lloyd Morgan (see his Habit and InstiTict), who 

 incubated the eggs of birds in the laboratory, and then 



