In the 17th Century, who carried out measurements along a meridian in the Netherlands using triangulation with one-minute precision, combining with endpoints' astronomic latitudes to determine Earth's size?

• A. Newton
• B. Snellius
• C. Cassini
• D. Euler

Answer: (B)

The measurement relies on using triangulation along a meridian to map a specific arc on the Earth and then tying that arc to the actual angular separation between two points in latitude, determined astronomically. By building a network of triangles across the Netherlands and measuring angles with high precision, you can compute the straight-line distances between survey points and thus the length of the meridian arc between two endpoints. Separately, you determine the latitudes of those endpoints through astronomical observations, giving the exact angular distance along the meridian between them. With the arc length and the angle between endpoints known, you can derive Earth's size (radius or circumference) from simple geometry s ≈ R·Δφ, where Δφ is the angle in radians. This combination of precise triangulation and astronomical latitude measurements was pioneered in the Netherlands by Willebrord Snellius, making him the correct figure for this era of geodesy. The other names are associated with different contributions or later work in other regions.