After Henry and Victor receive an invitation from a friend in Perth, Scotland, they continue traveling north through small towns in England.  Here, Victor encourages Henry to continue without him to Perth while he tours Scotland alone.  You can find the following quotations about two-thirds of the way through Chapter 19; I used an online text which I have cited as an external link.

The following shows the pair's travels into Scotland:

We left Edinburgh in a week, passing through Coupar, St. Andrew's, and along the banks of the Tay, to Perth, where our friend expected us.

Then Victor tells Henry to go on without him:

I told Clerval that I wished to make the tour of Scotland alone.

Henry begrudgingly accepts:

Henry wished to dissuade me; but, seeing me bent on this plan, ceased to remonstrate. He entreated me to write often. "I had rather be with you," he said, "in your solitary rambles, than with these Scotch people, whom I do not know: hasten then, my dear friend, to return, that I may again feel myself somewhat at home, which I cannot do in your absence.

I hope this helps!