Distances measured along erratic paths of coastlines, rivers and streams is done by an instrument called:

Question

Accepted Answer

The correct answer is Option 2: Opisometer. Here's why:

*   **Opisometer (also known as a curvimeter or map measurer):** This instrument is specifically designed to measure the length of curved lines, such as those found on maps representing coastlines, rivers, streams, roads, or any other irregular path. It consists of a small wheel that is rolled along the line to be measured. The instrument then converts the wheel's rotations into a linear distance, providing an accurate measurement of the curved path's length.

Now, let's explain why the other options are incorrect:

*   **Planimeter:** A planimeter is used to measure the *area* of a two-dimensional shape, not the length of a line. It traces the outline of the shape, and the instrument calculates the area enclosed within that boundary.

*   **Pluviometer:** A pluviometer (also known as a rain gauge) is an instrument used to measure the amount of rainfall over a specific period. It has nothing to do with measuring distances, curved or otherwise.

*   **Hydrometer:** A hydrometer is used to measure the specific gravity (relative density) of liquids. It determines how dense a liquid is compared to water. It is not used for measuring distances.

Therefore, the opisometer is the only instrument among the options that is designed for and capable of measuring distances along irregular or curved paths like coastlines, rivers, and streams.