① He saw a tall tree, some of the branches of which were broken.

= He saw a tall tree, and some of the branches of the tree were broken.

② She followed him down the corridor, at the end of which was the surgery.

= She followed him down the corridor, and at its end was the surgery.

③ He came to a town in the middle of which was a tall tower.

④ We observe only half the sky at one time, the other half of which is on the other side of the earth.

⑤ If you could write as fast as you speak, it would be an advantage. So people have turned their hands and heads to making simpler signs for sounds than our old alphabet. This is shorthand writing, by means of which people can keep up with the talker.

⑥ This is one of the few things in regard to which a good resolution would be absurd.

⑦ He set out on a dangerous adventure in the course of which he had to feel his way with the utmost care.