stop, and the bell becomes stationary, and then descends again slowly towards the block of stones. If they have been carried on a little too far, and want to retrace their steps, they communicate afresh with the men working on the surface, and the obliging machinery soon brings them to the exact point desired.” The diving‐bell has many times rendered service to engineers, by enabling them to descend and ascertain the nature of damages going on, which might otherwise have ruined their work. When Brunel was building the famous Thames Tunnel, and the current had broken through its arched roof, he went down in a diving‐bell to see for himself the extent of the disaster. After a descent of nearly thirty feet, he reached a serious opening in the masonry, but the hole was too narrow to allow the bell to enter. It was therefore necessary for some one to dive into it, and brave Brunel immediately declared his intention of doing it. Taking hold of the end of a rope, he plunged into the hole, where it is said he remained nearly two minutes, mentally noting the damage done. So intent was he on this examination that he let go the rope just as his companions above, alarmed at his long stay below, were hauling it up. He had just time to catch hold of it again, and was happily drawn safely into the bell. [Illustration: DIVERS ATTACKED BY A SWORD‐FISH.] The diving dress was a later development, and owed much of its present practical shape to French men of science. The object of the dress, which is of canvas or india‐rubber and metal, is, of course, to give each individual wearing it the utmost liberty of motion, while having at the same time a proper supply of vital air. The condensed air‐reservoir is made of steel, and capable of resisting great pressures. The diver carries this apparatus on his back; from it a respiratory tube issues, and is terminated by an india‐rubber mouth‐piece, which is held between the lips and teeth of the diver.