The year 1551 witnessed the diving machine invented by Nicholas Tartaglia which Davis describes as consisting of "...a wooden frame like that of a gigantic hour glass, to which a heavy weight was attached by a rope.

A man standing in the frame, with his head enclosed in a large glass ball, open only at the bottom, "wound himself down to the sea floor by turning a windlass on which the rope was coiled. Davis describes the device as "impracticable" and observes that it was not very clear just what the diver could do when he actually reached the bottom.

A few years ago, Al Giddings had a craftsman construct replicas of historical diving equipment, including a working model of Tartaglia's diving bell. Pete Romano demonstrated that he could descend in Tartaglia's device to a depth of 30 feet, recover an object on the seabed and return to the bell for a breath of air.

Although it worked, Davis was probably correct in suggesting the device was "impracticable," allowing the diver a scant few minutes working under water.

In 1616, the German inventor Kessler introduced his diving bell with glass ports and a ballast weight for stability, but could have proven hazardous. Many historians have observed that if the diver took one false step, the bell would probably capsize, drowning its occupant.

In the mid-1600s two interesting references to the use of diving bells appear in the literature of diving. One is a bell reported as being used during the voyages of a Spanish explorer, Don Francisco de Ortega in California (Mexico's Baja California) during the years 1632-1636.

Unfortunately, no illustration has been located of an invention attributed to Ortega, which he is said to have employed during his explorations. This was a diving bell described by the ship's scribe as being made of "wood and lead... so that one or two persons can go down in it to whatever depth without danger of being drowned, even though they remain under the water ten or twelve days."

This is a tantalising reference to what appears a most improbable device, unless de Ortega discovered saturation diving. It is impossible to confirm the report.

A more successful diving bell is the bell invented by Edward Bendall, a freeman of the colony in Massachusetts.

In the Journal of Governor John Winthrop, an entry dated 27 July 1640 reads: "Being the second day of the week, the Mary Rose, a ship of Bristol, of about 200 tons, her master one Captain Davis, lying before Charlton [Charlestown], was blown in pieces with her own powder..." with great loss of life to the crew.

The General Court contracted with Bendall to clear the harbour of the wreck. The Court gave Bendall "...the liberty to make use of any of the cables, and other things belonging to the worke, as he needeth, allowing hurt of them" and Bendall designed and built two wooden diving bells, "two great tubs, bigger than a butt, very tight, and open on one end, upon which there were hanged so many weights as would sink it to the ground (600 wt)" Bendall used the bells to make fast the cables, to recover the remaining cargo and ordnance of the sunken galleon. One giant cannon was brought to the surface and deposited in the lighter moored alongside.

The cannon created a good deal of curiosity because it was rumoured that treasures had been secreted in the barrels of the guns. Bendall, who had heard the rumours, did a casual search of each cannon, removing, from one gun a large padding of rope yarn which seemed strangely heavy. He thought that the weight had come from being waterlogged.

Bendall could not credit the idea that the ship's masters would put valuable gold and silver coins inside a cannon's mouth. Then one day he decided to test the cannon and rammed the rope yarn inside to use a wad for firing. At high tide the cannon was fired and a large array of coins exploded into the air, settling in the harbour waters.

The following day, at low tide, people walking the strand along the sandy beach were startled to see silver and gold coins gleaming in the sand and, of course, made free with the treasure. Bendall petitioned the General Court for a patent for his diving bell, probably the first in the Colonies, but was denied.

The Portuguese galleon Florencia was sunk, in 1588, as part of the Spanish Armada expedition, resting in Tobermory Bay, Mull. In 1665 an expedition used a diving bell to recover cannon, a feat discussed by George Sinclair, a Professor at Glasgow University, who, in 1669, published a book in which he described the bell used, attempting a rationale for the physics, physiology and engineering of a diving bell.

In 1678 a French physician, Dr. Panthot, described in detail the famous salvage of the ships sunk on the reefs off Catalonia, Spain, in the port of Cadaques (then called Capdaques). Two boats carrying a transverse beam between them supported the bell, which was made of wood. It was around thirteen feet high by nine feet across and the diver was seated on a crossbar in the middle of the bell. One of the two Moorish divers was able to work the bell for periods as long as two hours, but the other could not stand the heat generated in the bell, and thus was limited to around one hour of work. The divers' reward was to keep as many coins as they could hold in their hand and mouth.

Around the same time, in 1680, a report by the physiologist Giovanni Borelli, published posthumously, proposed a diving bell which was small and quite impractical. In an analysis by the mathematician, Bernoulli, the design was severely criticised as unworkable.

Borelli proposed, is a breathing tube, not unlike that of Lorini's, which Borelli preferred to the concept of a diving bell. It is likely that the user of the breathing tube would have been asphyxiated.

One of the more famous and successful applications of what must have been a primitive diving bell of the inverted container type, is that of William Phipps.

He was an American born in 1650 who convinced Charles II to provide him support to salvage a treasure lost when a Spanish ship sank of the coast of San Domingo.

His first efforts, in 1683, proved unsuccessful. He returned to England to raise money for another expedition, was refused by James II, but received support from the Duke of Albemarle.

He returned to the West Indies in 1687 and his efforts produced 200,000 pounds sterling, earned him a knighthood and eventually made him High Sheriff of New England. In 1689, the French physicist Denis Papin proposed what appears to be the first plan to provide air to the diving bell, under pressure, from the surface.

Papin's proposal, never realised in an actual working model, was to use force pumps or bellows to maintain a constant pressure within the bell. As we will see, the use of barrels of air for replenishment, used by Halley, continued for over a century until Smeaton introduced a successful force pump in 1788.

It is generally agreed that the diving bell invented by Edmund Halley is undoubtedly the forerunner of the modern diving bell. In 1690, Halley designed and built, of wood, a bell in the form of a truncated cone, with the larger end (diameter 5 feet) being open and the top (3 feet) closed.

In Smith's words, "It was poised with lead, and so suspended that it might sink full of air, with its open part downward, and has as nearly as possible in a situation parallel to the horizon-so as to close with the surface of the water all at once."

There was a clear glass port on the top for light and vision as well as a cock to let out the heated, breathed air. About three feet below the open end of the bell was a stage that was suspended by three ropes, each of which was weighted with 'about one Hundred Weight, to keep it steddy.'

The air was replenished by the use of two barrels, each containing thirty-six gallons. They were weighted with lead to sink them, and had a bunghole in the lower part to let in water as the air condensed on the descent and to let it out when the barrel was drawn up full. Another bunghole was placed in the top of the barrel to which a leather hose was attached.

This pipe or hose was prepared with beeswax and oil and was weighted to hang below the bottom bunghole so that no air could escape unless the lower part of the barrel was first raised. When the hose was moved under the bell, a diver could grab the end of the hose and lift it into the bell.

The pressure of the water forced the air contained into the barrel through the bottom bunghole up into the bell. Alternating the barrels, which were refilled on the surface, the barrels could be lowered and raised via tackles, providing a continuous supply of fresh air.

Using this technique, Halley stated that he and four other divers remained on the bottom for an hour-and-a-half at a depth of nine or ten fathoms.

Halley's method of replenishing the air was simple and effective and, in his essay The Art of Living under water he wondered why someone had not thought of it before. In fact, George Sinclair in his 1669 work had proposed sending air down to the bell in very much the same manner.

Halley suggested "an additional contrivance" for the bell. He proposed a means "...for the diver to go out of our engine to a good distance from it, the air being conveyed to him in a continuous stream by small, flexible pipes, which pipes may also serve as a clew to direct him back again when he would return to the bell." These divers would be fitted with a small, auxiliary bell over their upper body, fitted to the pipes from the bell. Thus was born the first diver lockout system.

In his discussion of Halley's bell, Davis suggests that Halley may have been aware of Papin's proposal to use force pumps or bellows to provide a continuous supply of air to the bell, but that Halley feared that, should he employ the device, Papin might accuse him of plaigarism.

It is indeed probable that Halley was aware of Papin's idea, inasmuch as Papin, a French physicist was a Fellow of The Royal Society, of which Halley was then Secretary.

Papin had written a brief essay, published in 1691, entitled How to Preserve a Flame Under Water in which he discussed a watertight lantern in which a candle burned to assist in night fishing.

In this essay he went on to say that this problem of a watertight container to which air needed to be conveyed led him to a consideration of improving the diving bell. He proposed a system with leather bellows fitted with valves and pipes through which the air could be forced. As he writes," Should these leather bellows not prove strong enough to set up the extra pressure required at great depths, the difficulty could always be got over by the use of pressure-pumps."

This appears to be the first time the use of forced air to replenish the bell was proposed but, as we noted above, Halley did not employ the technique and the use of barrels for replenishment continued for a over a century until Smeaton, in 1788, designed the first diving bell using forcing-pumps. Marten Triewald was a Swedish Army officer and architect to the king of Sweden, who in his report on The Art Of Living Under Water, published in Stockholm in 1734, acknowledges his debt to his "friend and patron," "the learned and ingenious Englishman Doctor Edmund Halley."

Triewald indeed took the name of his report, submitted to the "Supreme King Friedrich, King Of the Swedes, the Goths and the Wends, and Ruler Of Hesse" from the 1716 paper published by Halley in Philosophical Transactions.

Triewald offers a most interesting comment in his report which suggests very strongly that he may have been aware of Papin's proposal to send air down from the surface. "All those inventions based on supplying air in its natural air [sic] through tubes from the surface have no valid foundation and are generally devised by those totally ignorant of what they are dealing with."

So he continued Halley's system of replenishing air via alternating barrels. Triewald's bell, smaller and lighter than Halley's was made of copper rather than wood and was lined with tin. Lead weights were attached to the rim. Only one diver could use it at a time. Three strong iron chains attached to the rim suspended a plate on which the diver could stand (in a manner similar to the one attributed to Sturmius) and have his head just above the water level for air intake. Triewald also placed a spiral pipe fixed at the side of the bell through which the diver could breathe, no matter what his position.