Definition of "watch-glass" [watch-glass]

• A sand-glass used to measure the time of a watch, as on shipboard: usually a half-hour glass. (noun)
• A thin concavo-convex piece of glass used for covering the dial of a watch. (noun)

The Century Dictionary (Public Domain)

• "Leaning forward towards the gas-lamp, I tried the thing on my watch-glass, and scored a white line across that with the greatest ease."
• "The water when placed in a tumbler and agitated gave out sparks, but a small portion in a watch-glass scarcely ever was luminous."
• "The first conclusion had been arrived at by the presence of a lifeless flea caught up in the child's hair: combed out and placed under a watch-glass, the flea had taken an hour and a quarter to recover from its immersion in the water of the Kennet and Avon Canal, which was very close to the exact time required for the insect to revive after twelve hours 'exposure to a hostile and liquid environment."