The caption reads (translated):

With my learning, Ladies and Gentlemen, I should be working in a palace and it is out of dedication that I come to this square to disseminate my knowledge to the uneducated crowd that has the honor of listening to me.

In a second, it will be my honor to insert the thunder of god into a bottle; but first, I would like you to feel the soothing and pleasant sensation of electricity. If among the company of fools surrounding me there is some cripple or other, let him approach without hesitation, and I will electrify him instantly.

Come one and all, uneducated as you are, learn and be instructed, it costs only two sous; stand by, I am about to start!