A Minimum Thermometer is designed to measure and record the lowest temperature reached since the last reset. It uses a specialized mechanism that captures and retains the minimum temperature until it is manually reset. Here’s how a typical minimum thermometer works:

1. Construction: A minimum thermometer consists of a glass tube filled with a liquid, such as mercury or alcohol, that expands and contracts with temperature changes. The tube is typically narrow and has a bulb at the bottom containing the liquid. The upper part of the tube is sealed, creating a vacuum above the liquid.
2. Index Mechanism: Inside the glass tube, there is a constriction or a small portion of the tube with a narrow bore. Above this constriction, there is a small metallic index, usually made of a silver or steel thread. The index is attached to the liquid in the bulb and moves with the expansion or contraction of the liquid.
3. Expansion and Contraction: As the temperature drops, the liquid in the bulb contracts, and the pressure on the index decreases. This causes the index to move down the narrow bore. However, when the temperature increases, the liquid expands, and the index remains in its position due to the vacuum above it.
4. Retaining Mechanism: To prevent the index from rising due to expansion when the temperature increases, a retaining mechanism is employed. This mechanism can be a small magnet or a magnetized strip. The magnet attracts the metallic index, holding it in place even when the liquid expands.
5. Reading and Resetting: To read the minimum temperature, one needs to observe the position of the index against a calibrated scale on the thermometer casing. The index indicates the lowest temperature reached since the last reset. To reset the thermometer, a manual action is required. This typically involves tilting or tapping the thermometer to bring the index back to the mercury or alcohol level, erasing the previous minimum reading.

By using a minimum thermometer, individuals can track the lowest temperature experienced within a given time period, such as a day or a week. This type of thermometer is commonly used in weather monitoring stations, climate studies, and various industrial applications that require accurate temperature records.

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