Blackie's Greek Primer Questions

Textbooks Greek Textbooks and Study Groups
1

I’m confused about a few examples in Blackie’s Greek Primer, Lesson I. https://www.gutenberg.org/cache/epub/69656/pg69656-images.html#LESSON_I

ἀκούεις τοῦ ποταμοῦ; do you hear the river?
ἀκούεις τῆς βροντῆς; do you hear the thunder?

Neither of these seem to be using the accusative for the apparent direct object. As I see it, the possibilities are:

  1. These are typographical errors.
  2. The direct object is really the sound and can be left implicit, such that the sentence is really “do you hear (the sound) of the river?”

Which is the case?

2

You can find ἀκούω with the genitive of the thing heard.