t is one of the planes, and this lower part is the other.
This part out in front is that portion of the steering apparatus which
enables the aviator to guide the machine up or down, and this part at
the back is to govern the side-to-side movements. When the machine
stands on the ground it rests on these three little wheels, which are
like bicycle wheels. Here sits the aviator, and directly back of him
is the powerful little engine which sets the propeller whirling at the
rear. The machine makes a noise like a swift-running motor boat or a
motorcycle. It starts off on its wheels and rapidly increases its
speed until it rises from the ground and sails away gracefully into
the upper air. [Your drawing of Fig. 110 should now be complete.]

"As you look at this machine, remember that it is not at all like a
balloon. The bag of a balloon, filled with gas, is lighter than the
air; hence, it stays up without any trouble, unless the bag breaks and
lets the gas out. But the aeroplane has no gas bag; it is heavier than
the air and it must '_keep a-goin'_' in order to stay up at
all. Remember this: _Just as soon as the aeroplane stops, it comes
crashing to the earth_, like so many have done, bringing death and
destruction.

[Quickly detach your drawing paper from your board, turn it one-fourth
around and re-attach it with thumb tacks. With broad strokes of black
crayon indicate the foreground. Add lines of mountains, completing
Fig. 111.]

[Illustration: Fig. 111]

"You boys know how it is when you are riding a bicycle. Your wheel
will stay upright as long as you are pushing ahead, but as soon as you
stop the wheel topples over.

"Sometimes the aeroplane engine fails to work, sometimes a wire or rod
breaks, sometimes the aviator attempts to do some fancy flying which
throws the machine out of balance, sometimes the wind prevents the
machine from going on in its course. Any of these things may cause the
machine to stop going forward and come dashing downward.

"You, boys--and you, girls--and we older men and women, are just like
the aeroplane in one great particular. In the Christian life, in our
work, in our study, in our efforts to do good, we can never hope to
succeed and progress if we let anything stop us in the way. How truly
does all this apply to the Sunday School. The stand-still boy and the
stand-still girl never get anywhere. The stand-still Sunday School is
'a dead one.' Life in Sunday School means movement, forwa