ICSE Class 8 Answered

Franklin constructed a kite and attached a wire to the top of it to act as a lightning rod. To the bottom of the kite he attached a string, and to that he attached a silk string. The hemp, wetted by the rain, would conduct an electrical charge quickly. The silk string, kept dry as it was held by Franklin in the doorway of shed. He also, attached the metal key to the hemp of the string.While flying kite, Franklin noticed losse threads of the hemp string standing erect. Franklin moved his finger near the key and negative charges in the metal piece were attracted to the positive charges in his hand. Struck with the spark he immediately presented his knucle to the key. He percieved the evident electric spark. It is said that he collected the electric fire or electricity using Leyden jar which can be discharged later.

This is how discovered that clouds are electrically charged during the thunderstorm.