pressure, was tested by the weight required to crush it. This weight was furnished by a hydrostatic press, the pump of which was one inch in diameter: one pound at the end of the pump lever produced a pressure on the surface of the cube equal to 2·53 cwt., or to 71·06 lbs. on the square inch. These trials were made with caution; the weight on the lever was successively increased by a single pound; and, in order to ensure a gradual action, a minute was allowed to elapse previous to the application of each additional weight. It was noted for each specimen the pressure at which the stone began to crack, and also the pressure at which it was crushed. The results of all these experiments (which are stated for each stone) gave a decided preference to the Bolsover magnesian limestone, which was noticed as being remarkable for its peculiarly beautiful crystalline structure, while it was the heaviest and strongest of all the specimens, and absorbed least water. Its composition was 50 per cent. of carbonate of lime, and 40 of carbonate of magnesia; the remaining ten parts consisting chiefly of silica and alumina. An easy Method of determining whether a Stone will resist the Action of Frost. In the choice of a stone for building purposes, it is of the utmost importance to be able to determine, by a few prompt and easy experiments, whether the proposed stone is capable of resisting the destructive action of moisture and frost. The means of ascertaining this were difficult and uncertain, until M. Brard, several years ago, communicated his method to the Royal Academy of Sciences at Paris. This learned body having appointed a Committee of their own members to inquire into the merits of M. Brard’s process, and to make a report thereon, the united testimony of engineers, architects, masons, and builders from different parts of France, was received, and proved so favourable as to its merits and simplicity, that the Committee recommended the plan to public notice and general adoption. From their Report we select a few details, which hitherto, we believe, have not appeared in English.