The other, called the "hearth," was flat, about eighteen inches in length, half an inch thick, and three inches wide.

On its upper surface, close to one edge, were several slight cavities, each just large enough to hold the rounded end of the spindle, and from each was cut a narrow slot down the side of the hearth.

This slot is an indispensable feature, and without it all efforts to produce fire by wood-friction must fail.
Laying the hearth on the flat side of a sledge runner and kneeling on it to hold it firmly in position, Yim set the rounded end of his spindle in one of its depressions, and holding the upper end between the palms of his hands, began to twirl it rapidly, at the same time exerting all possible downward pressure.

As his hands moved towards the lower end of the spindle he dexterously shifted them back to the top, without lifting it or allowing air to get under its lower end.
With the continuation of the twirling process a tiny stream of wood meal, ground off by friction, poured through the slot at the side of the hearth, and accumulated in a little pile, that all at once began to smoke.

In two seconds more it was a glowing coal of fire.