24 THE FLIGHT OF BIRDS 



domestic Pigeons, and found that they account for 

 about one-fifth, or even more than one-fifth, of the 

 weight of the whole bird. Indeed, in one Wood- 

 Pigeon they were equal to three thirteenths of the 

 total weight — a little less than a quarter.* Hence 

 the centre of gravity lies considerably below, though 

 not so very far below, the shoulder joints. But the 

 idea that it is good to have the centre of gravity of 

 a flying machine low down is altogether a miscon- 

 ception, a fact that can easily be put beyond all 

 doubt by experiments with small gliders. Weight, 

 placed low, tends to make the machine oscillate 

 and even swing right round. It is best that it 

 should be on a level with the supporting surface. 

 In the case of the bird, the chief supporting surfaces, 

 the wings, are always changing their relative position 

 as they are raised or lowered, and, of course, as they 

 move they to some extent raise or lower the centre 

 of gravity. This must make voluntary adjustments 

 for the purpose of recovering balance still more 

 necessary. But Professor Marey has pointed out 

 a curious fact which may make these oscillations 

 less difficult for the bird to deal with. When the 

 down-stroke takes place and the wings are lowered, 

 the centre of gravity occupies a lower position in 

 the bird, but the bird as a whole, except during 

 very rapid flight, rises. With the up-stroke, on the 

 other hand, there is a raising of the centre of gravity, 

 but a lowering of the bird ; hence, though the bird's 



* Legal and Reichel, in the Jahresberichte der Schlesischen 

 Gesellschaft (1879), give ¥ .|^ ( = i^§ = more nearly | than A) as 

 the proportion of the total weight of the pigeon accounted for by 

 the three pairs of breast muscles; But this would seem to be a 

 mistake: Charadrius, according to them, comes next with f. 



