The irregularity of spacing has thus the effect of a convex lens, which accelerates the marginal relatively to the central rays.
Convex spectacles were invented towards the end of the 13th century.
In diameter, sessile, and generally in pairs, and are made up of large angular scales, slightly convex exteriorly, and with a sharp point in the centre.
In the disk plough, which is built both as a riding and a walking plough, the essential feature is the substitution of a concavo convex disk, pivoted on the plough beam, for the mould-board and share of the ordinary plough.
Most of the permeability-temperature curves were more or less convex towards the axis of temperature, and in all the experiments except those with annealed iron and steel wire, the permeability was greatest at the lowest temperature.