Shen Feng nodded slightly, understanding that this thing was indeed useful.
Although the people of this world had no common currency and mainly bartered, there was still a universal medium of exchange.
Glass lenses.
In truth, they were the bottoms of transparent glass bottles.
This kind of item was indispensable for people living at sea.
A single glass lens could serve a great many purposes.
Its greatest use was to focus sunlight, using the high temperature at the focal point of the convex lens to start a fire.
Another function was making telescopes to see things far away at sea.
For a sea vessel, a telescope was extremely important, whether for finding schools of fish or locating floating ore belts.
The sharp edge of the lens could even be used to cut through the tough skin of fish or scrape off scales.
And if a hole was drilled in the edge or it was wrapped in a leather casing, it could be worn as a beautiful necklace—a true symbol of power and status.
