August Schleicher 
Compendium of the Comparative Grammar of the Indo-European, Sanskrit, Greek and Latin 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. This book is a translation of those parts of Schleicher’s ’compendium der vergleichenden Grammatik der Indo germanischen sprachen’ which treat directly of the indo-european original language, Sanskrit, Greek, and Latin: it was undertaken for the use of students of Greek and Latin Philology, on the suggestion of Mr. Peile, m.a., of Christ’s College, Cambridge, to Whom I am indebted for several hints and corrections. My thanks are due to Herr Gustav Voigt also, for help kindly given.