290 M. Pasteur on Aspartic and Malic Acids. 



the case in astronomy. At the time of Ptolemy, the differences 

 of observation, which did not amount to more than three or fom* 

 minutes, were neglected, and the results thus obtained were false. 

 Tycho directed his attention to the investigation of those phse- 

 nomena which were within these limits of determination, and he 

 detected clearly-defined inequalities. Bradley narrowed these 

 limits to seconds of a degree, and within these seconds of variation 

 he found two of the most important phsenomena which have been 

 discovered by astronomers, — the nutation of the earth's axis and 

 the aberration of light. In the same way, thoiigh the chemists of 

 the present day have become able to recognise, to control, and to 

 characterize comparatively the results of the actions exercised by 

 different substances taken in sensible masses, the investigation 

 of the specific properties attached to the imperceptible corpuscles 

 of which they are composed is the most urgent requirement of 

 modern chemistiy, and one which offers a prospect of the most 

 important discoveries. This course is, for example, the only one 

 by which, in availing themselves of the rotatory powers, chemists 

 will be able to obtain reliable data for assigning symbolical foi*- 

 muijB to the complex products which constitute partial groups, 

 which are now the subject of so many contradictory interpre- 

 tations. 



M. Pasteur has pointed out in his memoir many details of 

 observation to which he was able to give only a passing attention, 

 haWng scarcely sufficient quantities of the various substances 

 upon which he operated to establish their fundamental distinc- 

 tions. In this respect his investigations have been completed, 

 for he has given the most positive evidence of the dissimilarity 

 of the molecular constitution of the isomeric products. But now 

 that this fact is well established, we avail ourselves of it for the 

 purpose of resuming the question under an inverse point of view ; 

 that is to say, in reference to those details themselves, which, in 

 the position it has now assumed, appear to us to have a special 

 importance. In fact, the two series of isomeric bodies which he 

 has obtained present these peculiarities, — that the corresponding 

 terms are formed by similar operations under parallel physical 

 conditions, and that they exercise reactions, the I'esults of which, 

 infinitely varied, can be always clearly distinguished. In this 

 similarity of formation and of physical conditions, the molecular 

 dissimilarity which he has established between the terms com- 

 pared cannot be accounted for except by conceiving that it results 

 from one or more of the three following conditions, — the mass of 

 the chemical corpuscles, their configuration, or the interior ar» 

 rangement of the similar ingredients of which they are consti- 

 tuted. The supposition of the inequality of the masses is excluded 

 here by the same test which renders it admissible in the case of 



