Sources of Heat.
What is heat?
Heat is that agent which causes the feeling of warmth.
Can heat be seen?
No; heat cannot be seen, it can only be felt.
When we touch a substance hotter than we are, what takes place?
A part of the heat from that substance comes to us and causes a feeling of warmth.
When we touch a substance colder than we are, what takes place?
A part of the heat from us goes to that substance, and we experience a feeling of cold.
Does the amount of heat in any substance vary?
Yes; water may be heated until it is scalding hot, or the heat may be taken from it until it is frozen into ice.
What causes a substance to become cold?
Taking away heat from a substance causes it to become cold.
Then what is cold?
Cold is only the absence or want of heat.
When we pass from a very hot room to one moderately warm, how do we feel?
We experience a feeling of cold.
When we pass from a very cold room to one moderately warm, how do we feel?
We have a feeling of warmth, although the room is no warmer than in the first instance.
How else can we prove that we judge of heat and cold by our feelings?
If one hand be held in quite warm water, and the other in quite cold water, for a few moments, and then both hands be plunged into tepid water, the tepid water will feel cold to the hand that was in the warm water, and warm to the hand that was in the cold water.
Is there anything without heat?
No; the coldest substance known still contains some heat.
How many kinds of heat are there?
There are two kinds of heat.
What are the two kinds of heat?
Heat accompanied by light, as the heat from the sun, or a lamp; and heat without light, as the heat from boiling water.
From what source does heat mostly come?
Heat mostly comes from the sun, which is also the source of light.
What is said of the heat and light from the sun?
Heat and light from the sun come together in the sunbeam.
From what other source is heat obtained?
Heat is obtained from the burning of any substance.
What else does the burning of any substance produce?
It often produces light.
Can the light and heat from the sun easily be separated?
They cannot easily be separated.
What does a glass window do with the light and heat of the sunbeam?
It permits both the light and the heat to pass into the room, so that we can see the one and feel the other.
Are the light and heat from a fire united, as they are in the sunbeam?
They are not; but they seem to be separated from each other.
What does a glass window do with the light and heat from a fire?
It permits the light to pass through; but it stops the heat.
How may this be proved?
When a pane of glass is held between the face and a fire, it will protect the face from the heat.
Is there any heat without light?
Yes; many substances contain heat, but do not emit light.
Does light change the amount of heat in a substance?
No; boiling water is as hot in the dark as it is in the light; and ice is as cold in the daytime as it is at night.
Is there any other source of heat?
Yes; heat is produced by rubbing or striking substances together.
What will result from rubbing two pieces of wood together?
They may be rubbed until they take fire.
How do Indians kindle fires?
By rubbing two pieces of wood together until they take fire.
How is heat produced by the brakes on railroad cars?
It is produced by the car-wheels rubbing against the brakes.
What may be seen when a horse strikes his shoes against a stone?
Small sparks of fire, which contain heat, may be seen.
If a piece of iron be hammered, will its heat be increased?
Its heat will be increased.
How can this be proved?
A person can, by hammering a piece of cold iron, make it red-hot.
Could we live without heat?
No; our bodies must be kept warm, and this can be done only by heat.
Is this true of other living things?
Yes; all the animals and all the plants would die if heat were taken away.
How should we feel in regard to these things?
We should feel thankful to an All-wise Creator, for having provided us with both heat and light from a never-failing source—the sun.