xpand. Hot-air balloons,
winds, and heating with hot-air furnaces, all depend on this principle.

SOURCES OF HEAT AND LIGHT

NOTES FOR A SERIES OF LESSONS

1. THE SUN.--Our dependence on it. Valuable results of its heat. Simple
notions as to its size, distance, and nature. Our earth catches a very
small fraction of the sun's heat; our sun is but one of millions--the
fixed stars. Show the burning effect of a lens.

2. FUELS.--Wood, oil, coal, alcohol, gas, peat, straw: where obtained;
special uses of each under varying conditions; need of economy. (This is
closely related to geography.)

3. ELECTRICITY.--In urban schools use the electric light or some heating
device for illustration. In rural schools a battery of two or three
cells (see "Apparatus") will melt a fine strand drawn from a picture
wire.

Applications: ironing, toasting, cooking; advantages or disadvantages
compared with gas or wood.

4. FRICTION.--Pupils rub hands together; rub a button on a cloth; saw a
string across the edge of a board or across the hand; bore a hole
through a hardwood plank, then feel the auger-bit.

Applications: restoring circulation; "hot-boxes" in machinery;
lubricants and their uses; lighting matches.

5. POUNDING.--Hammer a nail flat on an anvil or stone; feel it. Bullets
fired against an iron or stone surface may be picked up very hot. Note
sparks that can be struck from a stone; percussion caps, flint-lock
muskets.

6. PRESSURE.--After using a bicycle pump for some time, feel the bottom,
also the top. If possible, examine an air-compressor and find out the
means used for cooling the air.

7. SOURCES OF LIGHT.--Sun, moon, oil, tallow, gas, electricity, wax,
acetylene; advantages of each; relative cost.

PRIMITIVE METHODS OF OBTAINING FIRE: Most savages obtain fire by
friction; rubbing two pieces of wood together till hot enough to set
fire to some dry, light material. The natives of Australia placed a flat
piece of wood on the ground and pressed against this the end of a round
piece, which they twirled rapidly with their hands till fire was
produced. The North American Indians did the twirling with their bow
strings; the Eskimo's plan is somewhat similar. It is impossible to say
when flint and steel were first used, but we know they continued to be
the chief means of producing fire till about 1834, when matches were
invented. Let pupils try to produce fire by these means.

The earliest lamps consisted of shells, sk