Chemistry is the science which treats of the intra-atomic or the intra-molecu- lar changes which material things undergo under various influences. Mental is defined as "of or appertaining to the mind, including intellect, feel- ing, and will, or the entire rational nature." Science is knowledge gained and verified by exact observation and correct thinking. Mental chemistry is, therefore, the science which treats of the changes which material conditions undergo through the operations of the mind, verified by exact observation and correct thinking. As the transformations which are brought about in applied chemistry are the result of the orderly combination of materials, it follows that mental chemistry brings about results in a like manner.