474 POPULAR SCIENCE MONTHLY. 



shock of a headlong plunge into the water from a height of a hundred 

 to a hundred and fifty feet. Or, again, they equalize the internal and 

 external pressure when a soaring bird drops suddenly from a great 

 height, or still more often aid in oxygenating the blood. 



The hollow bones of birds are frequently cited as beautiful instances 

 of providential mechanics in building the strongest and largest possible 

 limb with the least expenditure of material, and this is largely true. And 

 yet birds like ducks, which cleave the air with the speed of an express 

 train, have the long bones filled with marrow or saturated with fat, 

 while the lumbering hornbill that fairly hurtles over the tree tops lias 

 one of the most completely pneumatic skeletons imaginable, permeated 

 with air to the very toe tips; and the ungainly pelican is nearly as well 

 off. Still it is but fair to say that the frigate bird and turkey buzzards, 

 creatures which are most at ease when on the wing, have extremely light 

 and hollow bones, but comparing one bird with another the paramount 

 importance of a pneumatic skeleton to a bird is not as evident as that 

 of a pneumatic tire to a bicycle. 



While it may not be easy to disprove Herr Gatke's assertion that 

 birds sustain themselves in the air by the exercise of some power be- 

 yond our own, it is pretty safe to assume that they do not, and it would 

 seem that the burden of proof should lie with those who take the 

 affirmative side of the question. 



If we have nothing to learn from birds in the way of building an 

 engine that shall exert great power for its size and weight we may still 

 have something to gain in the matter of speed, although here the popu- 

 lar idea is apt to be exaggerated. We often read that ducks fly at the 

 rate of a mile a minute, or that the swallow has a speed of two hundred 

 miles an hour, but it is very difficult to lay hands upon any facts that 

 will sustain these assertions. 



So, too, homing pigeons are frequently stated to have travelled for 

 long distances at the rate of sixty miles an hour, but some of the pub- 

 lished records show that one hundred and twenty miles in two hours 

 and a quarter is unusually fast traveling, and this is at the rate of only 

 nine-tenths of a mile per minute, a speed not unusual for express trains. 

 However, it may be said that actual observations show that ducks do 

 travel from forty to fifty miles an hour, and any sportsman will readily 

 believe that under some conditions they attain a velocity of a mile and 

 a quarter a minute, although a confession of faith is not a demonstra- 

 tion of an assured fact. 



So far the lesson taught by the bird is that a machine of low power 

 may attain a very considerable speed and it remains to be seen if there 

 is anything to be learned concerning methods of flight. Broadly 

 speaking, there are two, possibly three, distinct modes of flight, by re- 

 peated strokes of the wings and by soaring or sailing, although we find 



