thermoremanence

It also described an early form of the compass, a thermoremanence compass.

With a more efficient compass magnetized by lodestone, the thermoremanence compass fell out of use.

This was achieved by heating of metal (especially if steel), known today as thermoremanence, and would have been capable of producing a weak state of magnetization.

This was the 'south pointing fish' (a thermoremanence compass), essentially a heated iron (or preferably steel) object cut in the shape of a fish and suspended in a bowl of water.

It also described an early form of the compass (using thermoremanence), and had the oldest illustration of a Chinese Greek Fire flamethrower with a double-acting two-piston cylinder-pump that shot a continuous blast of flame.

Even before Shen Kuo and Zhu Yu had described the mariner's magnetic needle compass, the earlier military treatise of the Wujing Zongyao in 1044 had also described a thermoremanence compass.