How may electricity be called into activity?
By mechanical power, by chemical action, by heat, and by magnetic influence.
What is the most ordinary way of exciting electricity?
By friction.
Do we know any reason why the means above enumerated should develop electricity from its latent condition?
We are entirely ignorant upon this subject.
When you rub a piece of paper with India-rubber, why does it adhere to the table?
Because the friction of the India-rubber against the surface of the paper develops electricity, to which this adhesiveness is mainly to be attributed.
Does electricity present any appearance by which it can be known?
No; electricity, like heat, is in itself invisible, though often accompanied by both light and heat.