F. Bopp 
Comparative Grammar of the Sanskrit, Zend, Greek, Latin, Lithuanian, Gothic, German, and Sclavonic Languages [PDF ebook] 

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. The study of Comparative Philology has of late years hem cultivated in Germany, especially, with remarkable ability and proportionate success. The lahom’s of grimm, pott, bopp, and other distinguished Scholars, have given a new character to this department of literature; and have sub. Stituted for the vague conjectures suggested by external and often accidental coincidences, elementary principles, based upon the prevailing analogies of articulate sounds and the grammatical structure of language.