What experiments confirm the existence of two types of charges?
Electrical interactions can be observed experimentally. Let’s rub an ebonite (rubber with a large admixture of sulfur) stick with a piece of wool or fur. Let’s touch with a stick to a sleeve made of metal foil and suspended from a silk thread. Part of the charge from the stick goes to the sleeve. In the same way, we will supply the charge to the second same sleeve. We will bring the sleeves together by moving the tripods. We see that the sleeves are repelled. Since both shells are made of the same substance, charged from an ebony stick rubbed with the same piece of fur, it is obvious that they acquired charges of the same type. Experience shows that bodies with charges of the same kind repel each other. Take a glass stick and rub it with silk. Let us touch with a glass rod an electrically neutral sleeve suspended on a silk thread. We will bring the shells closer together, one of which is charged with a glass rod, the other with an ebony rod. The sticks will be attracted to each other. From this experience it can be concluded that the charge on the glass rod is different from the charge on the ebony rod. Therefore, there is another kind of electric charge.