Cosmic radiation has been discovered around 1911 by specialists of the conductivity of atmospheric air. In no theoretical or astronomical phenomena, not even in related phenomena, had been predicted, or even suspected, that cosmic rays exist. Their discovery resulted from the study of the causes generating a large quantity of ions in the atmosphere. In this article we review the scientific context at this moment and give a perpective of the participation of different actors. We sketch an inventory of the problem that is called the residual ionization of the air around 1900.
cosmic radiation; ionization; Wulf; Hess; Pacini
