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.