272 THE STRUCTURE AND LIFE OF BIRDS chap. 



have somehow to account for what seems to be a well- 

 established fact — viz., that the American Golden Plover 

 as it travels southward in autumn accomplishes over 

 1,700 miles in one flight. Even if we assume an 

 average rate of sixty miles per hour, the birds would 

 be over twenty-eight hours on the wing, and this is a 

 long time to be without food. 



Further experiments on the velocity of the flight of 

 birds of different species under varying conditions are 

 much to be desired. 



A pace of over 30 miles per hour is maintained by 

 race-horses over a short course. Ladas' time over the 

 Derby course, 1 J miles, gives him a velocity of 32 \. 



A Note on Flying Machines. 



It is difficult in writing of flight to leave unmen- 

 tioned the subject of flying machines. At the same 

 time, an elaborate account of them would be out of 

 place here. Not many years back it was supposed that 

 only in balloons was aerial navigation possible for 

 men, and the problem that was for ever being debated 

 was, How is it possible to steer a balloon ? With a 

 vehicle that travels with the air and has no velocity of 

 its own, steering is practically an impossibility. Since 

 this has been realised, attention has been diverted 

 from balloons to flying-machines, which are, necessarily, 

 heavier than the surrounding air, since, if they are to 

 do as they are intended to do, they must develop in 

 themselves energy sufficient to lift them from the 

 ground, and drive them forward, when required, in the 

 teeth of the wind. Naturally, the first idea has been 



