1844—1849 89 



of paratartrates would be explained by a structural law. The 

 first part of these conclusions was confirmed ; all the crystals of 

 tartrate proved to be hemihedral. But when Pasteur came 

 to examine the crystals of paratartrate, hoping to find none of 

 them hemihedral, he experienced a keen disappointment. The 

 paratartrate also was hemihedral, but the faces of some of the 

 crystals were inclined to the right, and those of others to the 

 left. It then occurred to Pasteur to take up these crystals one 

 by one and sort them carefully, putting on one side those which 

 turned to the left, and on the other those which turned to the 

 right. He thought that by observing their respective solutions 

 in the polarizing apparatus, the two contrary hemihedral forms 

 would give two contrary deviations; and then, by mixing to- 

 gether an equal number of each kind, as no doubt Mitscherlich 

 had done, the resulting solution would have no action upon 

 light, the two equal and directly opposite deviations exactly 

 neutralizing each other. 



With anxious and beating heart he proceeded to this experi- 

 ment with the polarizing apparatus and exclaimed, "I have 

 it ! " His excitement was such that he could not look at the 

 apparatus again ; he rushed out of the laboratory, not unlike 

 Archimedes. He met a curator in the passage, embraced him 

 as he would have embraced Chappuis, and dragged him out 

 with him into the Luxembourg garden to explain his discovery. 

 Many confidences have been whispered under the shade of the 

 tall trees of those avenues, but never was there greater or more 

 exuberant joy on a young man's lips. He foresaw all the con- 

 sequences of his discovery. The hitherto incomprehensible 

 constitution of paratartaric or racemic acid was explained ; he 

 differentiated it into' righthand tartaric acid, similar in every 

 way to the natural tartaric acid of grapes, and lefthand tartaric 

 acid. These two distinct acids possess equal and opposite rota- 

 tory powers which neutralize each other when these two sub- 

 stances, reduced to an aqueous solution, combine spontaneously 

 in equal quantities. 



'How often," he wrote to Chappuis (May 5), whom he 

 longed to have with him, " how often have I regretted that we 

 did not both take up the same study, that of physical science. 

 We who so often talked of the future, we did not understand. 

 What splendid work we could have undertaken and would be 

 undertaking now ; and what could we not have done united by 

 the same ideas, the same love of science, the same ambition ! 



