The precursors: Jacques Charles

Professor of experimental physics, Jacques Charles studied the expansion of gases and made the first aerostatic ascension with hydrogen on 2 August 1783. He was also the inventor of the solar megascope, a machine used to obtain a projection of images enlarged with objects illuminated by a set of mirrors.

Charles is thought to have conducted some photochemical experiments around 1789; unfortunately there are no contemporary records, or any written by him, about this, and the accounts that have filtered down are incomplete and not very clear.

Illustration:

Professor Charles’ experiment “We have had Charles’ curious experiment reproduced from the somewhat vague, somewhat incomplete accounts of the famous physicist’s time. – We assume in our engraving that the experiment begins: the silhouette of the character is cut out in black; a few moments later, the part of the paper that is represented in white will become black, and when the character withdraws, it is his shadow, currently seen in black, that will appear in white, since the light will not have reached this part of the silver paper”. (Gaston Tissandier, Les merveilles de la photographie, Paris, 1874).