Loose Needle Method in Surveying

The question asks to identify which surveying method is also known as the Loose Needle Method. This terminology is specific to compass surveying techniques, referring to how the magnetic needle is used during the measurement process.

Understanding the Loose Needle Method

In surveying, particularly with a compass, the Loose Needle Method is a technique where the magnetic needle is allowed to swing freely at each station where a measurement is taken. The reading of the bearing of the line is then taken directly from the position of the freely resting needle relative to the zero mark on the compass dial (usually corresponding to Magnetic North).

This method is characteristic of basic compass traverses where the magnetic bearing of each line is determined independently by letting the needle settle at each setup.

Identifying the Method

Let's examine the given options:

1. Chain and compass traversing: This method involves measuring the lengths of traverse lines using a chain or tape and measuring the magnetic bearings of these lines using a surveyor's compass. In standard compass traversing, the compass needle is allowed to swing freely to determine the magnetic bearing of each line. This aligns with the description of the Loose Needle Method.
2. Chain traversing: This method primarily involves measuring lengths using a chain or tape but typically uses angles (measured by a theodolite or similar instrument) rather than magnetic bearings measured by a compass with a free needle.
3. Traversing by fast needle: This is another compass traversing method, but it uses a "fast needle" or "fixed needle" technique. In this method, the instrument is oriented at each station by setting the compass to the bearing of the previous line (backsight) and clamping the needle. The bearing of the new line (foresight) is then read. This method uses a clamped or oriented needle, not a loose, freely swinging one for each new line bearing.
4. Plane table survey: This is a graphic method of surveying where field observations and plotting are done simultaneously. While a compass may be used for orientation (a trough compass), the fundamental method of determining lines is not based on reading bearings from a loose needle at each station in the same way as traditional compass traversing.

Based on the definition and comparison, the Chain and compass traversing method is the one that utilizes the Loose Needle Method for determining the direction of traverse lines by measuring their magnetic bearings using a freely swinging compass needle.

Therefore, the method referred to as the Loose Needle Method is Chain and compass traversing.