noun
water glass; underwater viewing box
A box-like device with a glass bottom used to observe underwater objects, such as fish or coral, from a boat or shore. Also called a hydroscope.
箱眼鏡で海の中をのぞくと、魚がよく見える。
When you look into the sea with a water glass, you can see the fish clearly.
子供たちは箱眼鏡を使って川底の石を観察した。
The children used a water glass to observe the stones on the riverbed.