Polar planimeter for measuring areas on a sphere! (Amsler, 1884)

Measures average radius of a curve from a point

By Green's Theorem this equals a quantity proportional to the electric potential at a point due to a region of uniform electric charge.

Radial Square Root Planimeter

What do these do?

Moment Integrator (Amsler, late 1800's)

Measures area, centroid, and moment of inertia

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