Pascal solved the hitherto refractory problem of the general quadrature of the cycloid, and proposed and solved a variety of others relating to the centre of gravity of the curve and its segments, and to the volume and centre of gravity of solids of revolution generated in various ways by means of it.
An abbot also had the power of excommunicating refractory nuns, which he might use if desired by their abbess.
Fire-clays include all those varieties of clay which are very refractory to heat.
As some of these substances (for example, lead sulphide and copper pyrites) are readily fusible when first heated, but become more refractory as part of the sulphur is dissipated and oxygen takes its place, it is important that the heat should be very carefully regulated at first, otherwise the mass may become clotted or fritted together, and the oxidizing effect of the air soon ceases unless the fritted masses be broken small again.
The materials used in the construction of furnaces are divisible into two classes, namely, ordinary and refractory or fire-resisting.