  On November 27, 1800, Thomas Young presents for the second time to the Royal
Society of London his theory of the musclurity of the crystalline lens, as
being the cause of the accommodation of the eye to different distances. This
question had indeed been the topic of his very first communication to the Royal
Society seven years earlier; from which he had been forced to withdraw in the
meanwhile by a series of articles claiming either the priority on his
discovery, or the demonstration of it being erroneous. Seven years later, Young
turns back to the topic with a very strongly elaborated text indeniably proving
the role of the crystalline in accommodation, as well as offering a new and
convenient method for measuring the amplitude of accommodation, discovering the
default of astigmatism of the eye, and setting the most precise and complete
measurement of the living eye of its time. For these reasons, and for the tight
intellectual connections between this text and the Theory of Light and Colours
Thomas Young will publish a year later, we thought it important to bring a
translation and commentary of this text at the disposal of the French audience.
