In this video from the British Museum, we see a "night clock" designed circa 1675. What's a night clock? Well, it's a grandfather clock designed to be read in the dark. It accomplishes this feat using fire.

This night clock features an unusual face that rotates numbers into position, rather than relying on rotating hands. That moving face allows the numbers to be cut out, such that light can shine through them, making the hours' numerals visible in the dark. (There are also little notches for minutes.)

The troubling design feature is that the face was originally illuminated by an oil lamp crammed inside the clock's case, behind the face. The case is made of wood.

In this video, British Museum curator Oliver Cooke notes that because of this fire-and-wood combo, there are only about five English night clocks still in existence. This model has had its oil lamp replaced by a modern electric light, hopefully preserving it for future generations.

Step back in time to an era when reading the time in the dark meant a real risk of burning your clock up: