What is the cause of hiccup?
If a towel be wetted with water, why does the wet portion become darker than before?
What is meant by Lancashire witches?
Does the dew rise or fall?
What is the principle of the hydraulic press?
Is there more oxygen in the air in summer than in winter?
What are those rings which we see round the gas and sun?
What is thunder?
How is it that a black hat can be moved by forming round it a magnetic circle, while a white hat remains stationary?
What is the cause of perspiration?