VII FLIGHT 179 
each, for their fixed point. The fact is that the dis- 
tinction between the fulcrum and the weight is an 
artificial one. The power applied acts on both ends 
at once, and if only one moves, or if one moves more 
than the other, we speak of the weight as being at 
that end. A weight at the other end which does not 
give, or gives less, we call the fulcrum. In a bird’s 
wing both ends move, but since the object is to obtain 
for the extremity as fixed a point as possible and to 
raise the body, the term fulcrum is reserved for the 
air. The bald statement, “ The air is the fulcrum,” is not 
incorrect, but it leaves out of sight a most interesting 
process. It is the rapid motion of the wing that wins 
for it a comparatively-fixed point, and throughout the 
process the air is being moved by a lever that has for 
its fulcrum the shoulder-joint. The oar, though a lever 
of the second order, presents the same difficulty, but in 
a less puzzling form. People who have never thought 
of the subject are apt if asked what is the fulcrum on 
which an oar works, to reply “the rowlock.” This is 
as much as to say that it is the aim of the oarsman 
to displace as much water as possible. It is only, 
however, by making the displacement of water a 
preliminary object, that he gains a fulcrum by which 
to move his boat. 
We must now consider the working of both wings 
at once. In order to understand this we may imagine 
a boat rowed by oars employed as levers of the same 
order as a bird’s wings. The rowlocks would be in 
the middle of the boat, and the oarsman would sit on 
either side holding the oars between rowlock and 
blade. They would have to face the bows, and this, 
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