It is little more than a century and a half ago since the celebrated astronomer, Halley—about the first to commence those experiments in submarine exploration which have been continued to the present epoch—descended to a depth of fifty feet in a diving‐bell which he had constructed. It was built of wood, and covered with sheet lead. The air that was vitiated by respiration escaped from the chamber through an air‐ cock, while the pure element was supplied by barrels, which descended and ascended alternately on both sides of the bell, like buckets in a well. These barrels, lined with metal, each contained some thirty‐six gallons of condensed air; they were connected with the interior of the bell by leathern tubes. As soon as one of these air receptacles was exhausted another was let down. Halley himself relates that in 1721, by the aid of this apparatus, he was able to descend with four other persons to a depth of nine or ten fathoms, and to remain under water an hour and a half. It is to Smeaton, the celebrated engineer of the famed Eddystone Lighthouse, that the diving‐bell owes its leading characteristics, as he was the first to abolish Halley’s rather clumsy contrivance and apply the power of the air‐pump; he also constructed the first cast‐iron bell. In 1779 he made use of the diving‐bell to repair the piles of Hexham Bridge, in the north of England, the foundations of the structure having been undermined by the violence of the current. A few years after a sad accident occurred from the use of Halley’s barrel apparatus. In 1783, Mr. Spalding, of Edinburgh, who had made some improvements upon the mechanical arrangements of Halley’s bell, but had retained the barrel air service, engaged to recover some of the cargo of an East‐Indiaman which had been sunk on the Kish Bank, Ireland. He and his assistant went down, and after the first supply of air was exhausted the barrels were sent down as usual. No signal having been given for some time, the bell was drawn up, and Mr. Spalding and his assistant were found to be dead. It is supposed that by some means they failed to discharge the air from the barrels into the bell, and were consequently suffocated. The barrel service was always more or less dangerous, from its liability to get out of gear, and if Spalding had adopted the invention of Smeaton, he would not have lost his life in the manner he did. The improved diving‐bell was soon generally adopted by engineers, and played an important part in the works which have so altered the port of Ramsgate. The great engineer Rennie made constant use of the diving‐bell in fixing the foundations of the eastern jetty, and in protecting it in parts against the attacks of the sea by a shield of solid masonry. It was extensively used in the construction of the Plymouth Breakwater. M. Esquiros, who visited the divers during the progress of that great work, gave an interesting account of their _modus operandi_:—