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.