"Keeping His Promise" by Algernon Blackwood

spirit lamp: an alcohol burner, like a weaker version of a Bunsen burner, burning alcohol (i.e. "spirits") rather than natural gas

Forth: here, refers to the Firth of Forth

"It was four o'clock": to the American audience, it may come as something of a shock, but in the summer, sunrise in the UK is around 4 or 4:30 am. For the British audience, it may be equally shocking to learn that sunrise in North America is, in the summer, more like 5:30 or 6am.

Arthur's Seat: an ancient volcano which is the main peak of the group of hills in Edinburgh, which form most of Holyrood Park. It is situated just to the east of the city center, about 1 mile to the east of Edinburgh Castle.

Holyrood Park: a royal park in central Edinburgh. It has an array of hills, lochs, glens, ridges, basalt cliffs, and patches of gorse. The park was created in 1541 when James V had the ground "circulit about Arthurs Sett, Salisborie and Duddingston craggis" enclosed by a stone wall.

The picture used is a late 19th century photo of the exterior of the University of Edinburgh's Old Medical School.

To follow along: https://www.gutenberg.org/files/14471/14471-h/14471-h.htm#chapter4