The prize founded by our late estimable associate Mr Keith, whose ingenious contrivances for self-registering thermometers and barometers are recorded in our Transactions, is, by the regulation of his Trustees, to be adjudged biennially for the most important discovery communicated to the Royal Society, or in the event of such being wanting, for the best paper which shall have been presented to the Society in the space of two years on a scientific subject. The Council, in discharge of the powers vested in them, have awarded unanimously the Keith prize for the last biennial period, to Professor Forbes, for his paper "On the Refraction and Polarization of Heat,” which they consider to come under that class of communications, which contain discoveries important to science.