Final answer:
The instrument used for measuring time by the flow of sand is referred to as a Sandglass, also commonly known as an hourglass. It was particularly used before mechanical clocks were invented.
Step-by-step explanation:
The instrument used for measuring time by the flow of sand is named a Sandglass. This is also known as an hourglass. These devices are shaped like two connected glass bulbs, with sand trickling from the upper to the lower bulb under the force of gravity. When all the sand has flowed into the bottom bulb, a certain amount of time has passed, usually an hour—hence the name hourglass. This form of timekeeping was especially prevalent before the invention of mechanical clocks.
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