Diving bells. 19th-century illustration of several designs of diving bells. At lower left and at right, is British engineer Charles Spalding's diving bell. This diving bell consisted of a lead-covered truncated wooden cone, 2.4 metres in height. It is seen being lowered from a rowing boat next to a sailing ship. The two small barrels are raised and lowered alternately to supply fresh air. One of these is seen renewing the diving bell's air supply. The other two diving bells are designs by Swedish engineer Marten Triewald (centre left) and English scientist Edmond Halley (upper left). This copper plate engraving was published in an 1810 volume of 'The New Encyclopedia' (Low's Encyclopedia, New York, 1810) by E. Low.