20 LOUIS PASTEUR. 



the inquiry. M. Biot then prepared the solutions in 

 well-measured proportions, and at the moment of 

 observing them in the polarising apparatus he invited 

 me again to come into his study. He placed first in 

 the apparatus the most interesting solution, that which 

 ought to deviate to the left. Without even making any 

 measurements, he saw, by the mere inspection of the 

 colours of the ordinary and extraordinary images of the 

 analyser, that there was a strong deviation to the left. 

 Visibly moved, the illustrious old man took my arm 

 and said, "My dear child, J have loved science so well 

 throughout my life that this makes my heart beat." ' 



The emotion of M. Biot was all the more profound 

 because he had been himself the first to discover the 

 rotation of the plane of polarisation by chemical sub- 

 stances, and had, for more than thirty years, affirmed 

 that the study of these substances and of their action 

 in regard to rotatory polarisation was, perhaps, the 

 surest means of penetrating into the intimate consti- 

 tution of bodies. His counsels were received with 

 deference, but they had never been followed out. And 

 now there appeared before the old man, already some- 

 what discouraged, a youth of twenty-five, who from his 

 first investigation had proved himself a master, who 

 had dissipated the obscurities of the famous German 

 note, and created a new chapter in crystallographic 

 chemistry. The composition and nature of paratartaric 

 acid had been explained, and a new substance, the 



