**Evaluating** each other, the three creatures stood in tight silence before Rhyn spoke at last.

Archimedes contributed to the knowledge of these curves by determining the area of the parabola, giving both a geometrical and a mechanical solution, and also by **evaluating** the ratio of elliptic to circular spaces.

The most important improvements in connexion with electrometers are due, however, to Lord Kelvin, who introduced the guard plate and used gravity or the torsion of a wire as a means for **evaluating** the electrical forces.