Aeroplanes

MASS AN ELEMENT IN FLYING.--The boy who reads this will smile, as he tells us that the power which propelled the ball through the air came from the thrower and not from the ball itself. Let us examine this claim, which came from a real boy, and is another illustration how acute his mind is on subjects of this character.

We have two balls the same diameter, one of iron weighing a half pound, and the other of cotton weighing a half ounce. The weight of one is, therefore, sixteen times greater than the other.

Suppose these two balls are thrown with the expenditure of the same power. What will be the result! The iron ball will go much farther, or, if projected against a wall will strike a harder blow than the cotton ball.

MOMENTUM A FACTOR.--Each had transferred to it a motion. The initial speed was the same, and the power set up equal in the two. Why this difference, The answer is, that it is in the material itself. It was the mass or densi