What was the major preoccupation of linguists during the nineteenth century

[alkafeel]

The major preoccupation of linguists was the historical study of languages ...more generally described as philology

فقه اللغةPhilology

What was the term or form which had been used to describe the common ancestor during the nineteenth century

The term which had been used to describe the common ancestor was proto

اصليProto

Proto of certain language refering to to the source of a language

Indian sub-continent -----proto Indo

European -----proto European

So we can combine them in one term (Proto-Indo –European)