ULTIMATE CONSTITUTION OF MATTER 89 



before a mirror, a model of the laevo-rotary acid is seen. Of 

 course we know nothing as to the real form of any molecule, 

 but we may claim to have something better than a vague 

 idea of what the molecules of different substances are rela- 

 tively like. The science of stereochemistry is the product 

 of a vast amount of chemical, mathematical and physical 

 research. Already very complicated molecular figures have 

 been worked out, and the subject promises most important 

 generalisations in the future. 



