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Guglielmo's Secret: the Enigma of the First Diving Bell with
Underwater Breathing Apparatus
Joseph Eliav
Abstract
The earliest employment of a breathing apparatus in underwater archaeology took place in
July 1535, when Guglielmo de Lorena and Francesco de Marchi explored a Roman vessel sunk
in Lake Nemi near Rome using a one-person diving bell that Guglielmo had invented.
Francesco's book on military architecture contains first-hand documentation of the exploration
and of the diving bell, which was very small, so that the air it contained could support a diver
for only a few minutes at shallow depths. The bell had an underwater breathing apparatus, a
mechanism that expelled breathed air while maintaining sufficient air pressure inside to prevent
the water level from rising and allowed the diver to work submerged for hours. This was the
first such mechanism that actually worked: it is certainly the most intriguing feature of the
diving bell. Unfortunately, Francesco mentions this mechanism but he refrained from
describing it because he had taken an oath to keep Guglielmo's invention a secret, which this
article sets out to unveil.
Introduction
Two Roman barges lay for many centuries at the bottom of Lake Nemi, a small lake in a
volcanic crater some 30 Kilometers south of Rome. Each barge was some seventy meters long
and 20 meters wide at the beam; they served as platforms for floating palaces, built for Emperor
Caligula in the first century AD. The palaces were in ruins but the wooden hulls were virtually
intact, presumably indicating intentional destruction and scuttling. These barges were the
objective of the first two instances of underwater archaeology on record.
In 1446, Cardinal Prospero Colona, driven by Humanist interest in anything Roman,
commissioned renaissance scholar Leon Battista Alberti to explore the ships. Genovese seamen
who "swam like fish" attached ropes to one of the ships and Alberti attempted to raise it by
means of cranes built on floating platforms (Biondo, 110-11). He obviously did not realize how
large and heavy the ship was, so all he managed to do was to break off and bring to the surface
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a piece of the stem and some planks from the bow. Incidentally, this was the first damage
inflicted to the ships by would-be explorers, later explorations, particularly in 1827 and 1895,
caused substantial harm (Speziale, 1929). Alberti mentions this exploit very briefly in his Ten
Books on Architecture (Alberti, Book V Chapter XII); he described it in more detail in another
book, named Navis, which is now lost.
In 1535, Guglielmo de Lorena and Francesco de Marchi used a diving bell invented by the
former to explore the same ship from end to end; they collected and brought to the surface
pieces and items they found on the ship, they observed many details of the construction and
they even measured the length, beam and depth of the hull. Francesco de Marchi has left a
detailed account of the exploration and of the findings in his book on military architecture
(Francesco de Marchi, 356-66). He has also left a detailed description of the diving bell
(Franceso de Marchi, 370-4), which starts with a statement that it had a mechanism that
expelled breathed air and prevented the water level from rising, but he had taken an oath to
keep it a secret.
Alberti deserves credit for performing the first act of aquatic archaeology ever. His was not
the first attempt to salvage a sunken ship but it was the first undertaken for the sole purpose of
learning about it. Guglielmo de Lorena and Francesco de Marchi deserve credit for being the
first to practice archaeology underwater using a breathing apparatus. Diving bells had been
used before for military purposes and for salvage; even Alexander the Great allegedly used one
in the siege of Tyre. Early Modern authors, including Leonardo da Vinci, describe various
devices for air supply to submerged divers, mainly masks or helmets with (too) long snorkels,
but this was the first actual use of an underwater breathing apparatus in a diving bell.
In 1927-1932, Italian archaeologists, with the support of Mussolini's government, drained
the lake and exposed the two vessels, removed piles of construction debris from the bilges,
extracted the hulls from the mud and transferred them to a museum built nearby. Artillery fire
eventually set them on fire in 1944, but we now have detailed documentation and
measurements of the ships, published in Le Navi di Nemi by Guido Ucelli, the archaeologist
who was in charge of the entire operation (Ucelli 1950). Therefore, the archaeological findings
of the early explorations are not very interesting.
Gugliermo de Lorena's diving bell is much more intriguing.
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The Diving Bell
Francesco de Marchi made several dives to the ship and his companion made several more.
He describes explicitly the first two dives he made on July 15, 1535; one lasted for half an hour
and the second for about an hour. It is evident from his description of the ship, from the detailed
observations of its construction, from the way they measured it and from the two mule-loads of
material they brought to the surface that they made multiple dives with a cumulative duration of
many hours. De Marchi writes that typical diving time was between one and two hours, the
limiting factors being cold and fatigue, not shortage of air. Apparently, there was an ample
supply of air in the diving bell but de Marchi refuses to tell how that was accomplished. On the
other hand, the compact size of the bell, according to the dimensions he does provide, proves
that the air it contained was enough for only a few minutes. This is the enigma of de Lorena's
diving bell.
De Lorena's invention was a small personal diving bell or perhaps a large diving helmet,
suspended by rope from a boat or floating platform, supported on the diver's shoulders and
reaching only down to the middle of his upper arms above the elbows. The diver could walk
around on the bottom with the bell on his shoulders and his hands and arms were free to do
work, but he had to be very careful to keep the bell in an upright position at all times. Walking
and working while balancing the heavy and clumsy contraption on the shoulders must have
been quite difficult and time consuming but it was obviously feasible. The divers walked all
over the ship, which was about 70 meters long, but refrained from going below deck for fear of
losing their balance. They used strings to take measurements of the ship and collected two
mule-loads of timber, nails, lead pipe, bricks and other items they found lying around. The total
amount of diving time and work required for doing all that must have been extensive; this was
certainly not a quick-look dive. According to de Marchi, Guglielmo de Lorena had used his
diving bell to find a sunken galley near Civitavecchia and to salvage its artillery, which must
have involved a significant amount of walking and working underwater.
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Figure 1:Gugliermo de Lorena's Diving Bell
This is how Francesco de Marchi describes the diving bell:
"The oath I have taken prevents me from explaining the mechanism by which the exhaled
air exited the instrument and water could not get in. This instrument was a round barrel made of
oak two fingers (about 4.5 centimeters) thick. It was five palms (about 1.25 meters) long and
three palms (about 75 centimeters) wide, with a securely fastened bottom, which, when in the
water, remained at the top. Six iron hoops held the barrel together with another hoop made of
lead more than two fingers thick installed around the open end to make the vessel sink better.
The outside was caulked and greased like a ship to make the vessel watertight. The person
inside could look out through a thick piece of crystal, one palm long and half a palm wide set in
the sidewall. Two strips of iron embraced the shoulders of the person inside so that the head
would not reach the bottom (i.e. top). A girth attached to these strips went down behind the
back and between the thighs; it was attached to the sidewall in front by means of a clasp, which
could be opened very easily... The instrument did not extend below the middle of the upper
arms, so that it was possible to work (with the hands) but almost by groping due to the lack of
sufficient light… Out of the water, this instrument was too heavy for a single man to carry;
underwater it seemed to weigh not more than 40 lb. due to the air trapped inside… This
instrument was useful for staying one or two hours under water… It was possible to work under
water, to saw, cut, tie ropes, operate hammers and other tools, but without much force due to
the (resistance of the) water… From the waist up, it felt as if one was in a hot oven but from the
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elbows down one felt a great cold… The breath (i.e. exhaled air) exited the instrument and
water did not enter but there was no tube or pipe for connection with the air out of the water."
According to the dimensions in Francesco's description, the internal volume of the diving
bell was 0.41 cubic meters. The upper part of the diver's body took up a small fraction of this
volume so a volume of 0.4 cubic meters (400 Liters) is a good-enough approximation for our
estimates.
The oxygen intake increases linearly with the intensity of physical exercise; actual
consumption by each individual depends on his or her fitness and body size. The oxygen
consumption of a 'booted' diver, i.e. a diver wearing a helmet and heavy boots, walking on a
hard bottom with no mud, has been measured at 1.5 Liters/minute STPD (Standard
Temperature and Pressure, Dry) i.e. normalized to atmospheric pressure, 0°C, with no
humidity (NOAA, Fig. 3-10). Working underwater while balancing the heavy diving bell on
one's shoulders was surely at least as strenuous as the task of the booted diver; a similar
consumption is a reasonable, perhaps even a conservative assumption.
Endurance, or the length of time a diver could stay submerged in the bell, depends on
whether some ventilation device existed, through which exhaled air could exit the bell. With
such a device, the concentrations of oxygen and carbon dioxide in the inhaled air would be
constant but the volume of air in the bell would decrease and the water level would rise with
every breath. When the water level in the bell rose to the level of the diver's mouth, he would
no longer be able to breath. The volume of air in the bell from the initial water level to the level
of the diver's mouth, divided by the volume he exhaled per minute would set the absolute upper
limit on endurance. If the diver exhaled into the bell and air did not get out then the volume
would remain constant but the concentration of oxygen would decrease and that of carbon
dioxide would increase; these concentrations would then set the limits on endurance. When
either one of these concentrations reached a certain threshold, the diver, especially one engaged
in a physically strenuous activity, would experience increased breathing rate, accelerated heart
beat, impaired coordination, chocking sensation and other adverse symptoms (OSHA par. d 2).
At an exertion level that requires oxygen consumption of 1.5 Liters/minute in STPD
conditions, the Respiratory Minute Volume (RMV), namely the volume of air breathed-in per
minute, is around 35 Liters (NOAA, Fig. 3-10). At this rate, the initial air volume of 400 Liters
in the bell could apparently suffice for 12 minutes. However, the volume of air inside the bell
decreases linearly with increasing pressure. At a depth of 10 meters, the pressure is two
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atmospheres, absolute, and the volume of the air in the bell decreases to half its volume at
atmospheric pressure. This means that the water level inside would rise to half the height of the
bell, 61 centimeters above the rim. We know from de Marchi that the lower rim of the bell was
above the elbows, to allow use of the hands during the dive. According to anthropometric data
(NASA Appendix B), the distance from a spot half the length of the upper arm above the
elbow, where the lower rim of the bell was, to eye level is about 0.215 the height of the
individual. Variation of this ratio with the height are negligible, it is 0.22 for a person 1.5
meters tall and 0.213 for one 1.95 meters tall. For a man 1.7 meters tall, which was the average
height at that time, this translates into 36 centimeters. Simply put, if the water level in the bell
rose by 61 centimeters it was above the height of diver's nose and he drowned. When the
Italians drained the lake to expose the ships, the first one broke the surface as the level dropped
by 5 meters and the bottom was exposed when the water level dropped by 12 meters; the depth
of the second ship was a between 15 and 22 meters (Speziale, 338). Assuming that the divers
explored the first ship, which was also closer to the shore, they had to descend to at least 10
meters, which the rising water level inside the bell would not allow. Even at smaller depths, say
5 meters, the diver's mouth and nose would be below water level within two minutes.
This simple analysis shows that the diver could not just breathe the air trapped inside the
bell, there had to be a way to remove exhaled air and replace it with fresh air, which is in line
with De Marchi's reference to a mechanism "by which exhaled air could exit the instrument."
The analysis shows more than that; it shows that air had to be somehow injected into the bell as
the depth increased, just to keep the water level from rising and drowning the diver; 400 Liters
of air (STPD) had to be injected before the diver could reach a depth of 10 meters.
The Air Supply Mechanism
Francesco states that the secret mechanism kept the water level from rising and that they
were able to dive for two hours. To achieve that, the mechanism had to be capable of
continuous or frequent supply of fresh air to the submerged diving bell while removing the
exhaled air. The newly supplied air would keep the volume of air, and the water level, inside
the bell more or less constant; it would also provide the diver with sufficient breathing air for as
long as he could stay under water before cold and fatigue forced him to the surface.
Thus, we know what Guglielmo's secret mechanism did but we do not know how it
worked, but we can use the few hints that his companion's text does provide to put together a
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ΔP
plausible assumptions about the nature of that mechanism. There are actually two mechanisms
to consider, one for removing exhaled air and the other for replenishing the bell with fresh air.
Francesco writes that the exhaled air (the 'breath') exited the diving bell. This means that
the diver inhaled compressed air from the diving bell and exhaled it into a device that allowed it
to get out to the surrounding water. That could be simple enough; the diver could inhale
through his nose and exhale through his mouth into a tube going through a hole in the roof of
the vessel, sealed all around to keep the vessel airtight. The pressure in the tube would be the
same as the pressure inside the bell and in the diver's lungs; the outlet of the tube would be
higher and therefore the pressure there would be lower. With the diver's lips serving as a valve,
this tube could let the exhaled air out into the water, working like a snorkel in reverse. A valve,
probably also in the roof of the bell, that the diver could open to let out air, is another possible
solution. The figure below shows a notional example of such a valve.
Figure 2: Notional Design of a Ventilation Valve
The air pressure inside the bell was equal to the water pressure at the depth of the water
level inside and therefore higher than the pressure of the water on its top. This difference in
pressure kept the valve shut (left figure). The diver could pull the rod down to open the valve,
let some air out and then close it again. The air ejected from the bell would be mostly exhaled
air, which was warmer than the rest of the air in the bell and therefore at its top.
Which of the two solutions did Guglielmo use? His companion gives us an answer, albeit
in a roundabout way.
In one of his dives, Francesco de Marchi took some bread and cheese into the bell. Perhaps
it was lunchtime or perhaps, as a contemporary wit said, as a native of Bologna, de Marchi
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could not conceive being, even for a short while, where food was inaccessible. In his own
words: "I brought with me, to eat, four ounces of bread and one of cheese. The bread, being
black and not fresh, crumbled and many fish rushed at me to eat the crumbs. The worst was
that, since I did not wear pants, they bit me in that part that anyone can imagine". A person
cannot eat bread and cheese with a tube attached to his mouth; therefore, this little anecdote
precludes the possibility of an exhalation tube. However, one wonders why de Marchi decided
to share this piquant but embarrassing episode with posterity. Furthermore, he writes that
looking through the glass window implanted in the sidewall of the bell, the fish seemed to be as
long as his arm, whereas in reality they were the size of his little finger. The glass could have
acted as a lens, but it is hard to believe that he could explore the ship from end to end, collect so
many items and observe the details of its construction while looking through a lens that
magnified observed objects more than tenfold. The episode of the fish and bread should
probably be taken with a grain of salt.
Francesco de Marchi was quite obsessive about keeping the secret of his companion's
invention. After somebody stole from his house the findings he had brought up from the bottom
of the lake, Francesco wrote that the theft was really an act of industrial espionage; the thief
was only trying to discover the secret mechanism. It is conceivable that he wrote the episode
only to disguise his secret, in which case the mechanism was an exhalation tube. On the other
hand, if we accept the episode as true, the mechanism had to be some sort of valve.
Either way, the mechanism could get rid of the exhaled air but it would cause the water
level inside the bell to rise, since the quantity of air inside the bell would decrease while the
pressure remained the same. Francesco was aware of the linkage between ejected air and rising
water level; he says explicitly that the secret mechanism allowed air to exit without letting more
water in. The only way to do that is to bring in more air from outside.
Air can be pumped into a submerged vessel via a snorkel or it can be transported down in
some containers. More than a century and a half after Guglielmo's time, Denis Papin invented
the first method. Others, including Leonardo da Vinci and Battista della Vella had 'invented' the
snorkel earlier, even Aristotle mentions it, but using lung suction alone, their snorkels would be
useless even at a depth of one meter. In 1689, Papin suggested pumping air into a submerged
diving bell with bellows and a flexible tube. His method failed because the bellows of his time
were not powerful enough. Even if bellows could be powerful enough to drive air into
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Gugliermo's bell, Francesco dismisses this possibility by stating explicitly that there was no
tube going from the bell to the surface.
Edmund Halley implemented the second method a quarter of a century later, in 1714. Like
Papin, he did not invent the method, Aristotle describes large cauldrons lowered into the water
vertically, with their bottoms up, so divers could periodically swim to one of the cauldrons,
insert their heads inside, take a breath and swim back to look for pearls or sponges (Marx, 30-
35). Halley resupplied a submerged diving bell with air carried in casks, open at the bottom like
small diving bells and lowered from the surface. When a cask reached a depth below the diving
bell, the pressure inside was higher than the pressure in the bell and the air rushed into the bell
through a hose. With two alternating casks, one going up while the other went down, Halley
had a continuous supply of compressed fresh air that allowed diving for long periods of time.
Additionally, with supply from many casks, the pressure in the bell was high enough to keep
the water level inside the bell close to its bottom rim. All the while, a valve in the roof of the
bell let out hot, breathed air.
Halley achieved exactly what Francesco de Marchi had insinuated: a mechanism that let
exhaled air out of the bell and kept the water level inside from rising, without a tube to the
surface. Is it possible that Guglielmo de Lorena invented Halley's method nearly two hundred
years before Halley?
Unless we suggest a viable alternative to Halley’s method for replenishing the air in a
submerged diving bell and keeping the water level down without a snorkel of some sort, we
must admit that this is the only possible solution to the enigma of Gugliermo de Lorena's diving
bell.
Only circumstantial evidence supports the argument that Gugliermo used the method
Halley would invent some two hundred years later. However, there was nothing in Halley's
invention that de Lorena could not accomplish with the technology available to him, given the
same design idea. The idea is the key. The hypothesis assumes that two engineers who faced
the same problem and possessed the same technology came up with the same design idea,
which is not a far-fetched assumption at all. Furthermore, they both could have taken the idea
from Aristotle.
The facts are:
a. There had to be a way to supply fresh air to the diver, otherwise he would be
able to stay submerged for only a few minutes at a shallow depth whereas
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Francesco de Marchi writes, from personal experience, about dives of one to two
hours at depths from 5 to 12 meters.
b. Francesco unequivocally excludes a snorkel solution.
c. An undisclosed mechanism existed; it was capable of expelling breathed air and
maintaining the pressure and volume of the air in the bell constant in spite of the
expelled air.
d. Halley's method was the only mechanism for replenishing the air in the bell and
for maintaining the pressure
e. Gugliermo de Lorena had the technology required to implement Halley's method
Considering these facts, the hypothesis that de Lorena used Halley's method is more than
just plausible.
By this hypothesis, de Lorena used two diving bells, not one. De Marchi describes the first;
his oath prevented him from writing about the second. The diver donned the main bell, actually
more a helmet than a diving bell, as de Marchi describes. The second bell, an inverted cask with
an open bottom, a hoop of lead around the open end and a plugged tube sticking out of its top
lid, travelled periodically up and down, into the water and back to the free air above. As the
cask descended, the air pressure inside increased, when it reached below the diving bell the
pressure in the cask was higher than the pressure in the bell. All the diver had to do was to grab
the cask, pull it so that the tube was inside the bell and remove the plug to let the compressed
air from the cask into the bell. Then, the assistants in the boat above would pull the cask out of
the water. By repeating this procedure, the diver had a continuous supply of fresh air and could
stay submerged as long as the cold water and his fatigue allowed. The diver could expel the
breathed air by periodically operating a valve or by exhaling into a tube, like a modern snorkel
in reverse.
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Figure 3: Mechnism of Air Supply
This mechanism contains some hypotheses within a hypothesis. Gugliermo could use
containers made of animal skins instead of a cask, but those would have to be inflated, probably
by means of a bellows. A cask was simpler and, having devised the diving bell, he surely knew
how to make and use a cask. Halley used a flexible hose longer that the cask with lead weights
at its end, not a plugged tube, to transfer air from the cask to the bell. The plugged tube is
simpler, it works just as well and for a diver who can move around and use his hands and
forearms in the water rather than being inside the bell like Halley's divers, it is easier to
Descending air cask
Air cask in position
Plugged tube
Open tube
Exhaust valve
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manipulate. Halley had to use an exhaust valve because his bell was large and usually held
more than one diver. Gugliermo's device served a single diver and therefore both a valve and a
reverse snorkel were viable solutions. The snorkel was simpler to implement but the valve was
more convenient to operate; and, if we grant any credibility to Francesco's bread and cheese
episode, we must conclude that Gugliermo used a valve.
Each ventilation solution required a different mode of operation. With the snorkel, the
diver would release air continuously and the water level in the bell would rise until the next
cask arrived with a new load of air. With a valve, the diver could breathe normally and open the
valve to ventilate the bell only when a new cask arrived. For an RMV of 35 Liters per minute
STPD, as used above, and assuming an air cask with a volume of 100 Liters, the assistant in the
boat would have to raise and lower the cask once every three minutes, which is quite easy to do.
Conclusion
If we accept Francesco de Marchi's text as factual, and we have no reason to believe
otherwise, some version of Halley's invention is a plausible solution to the enigma of
Guglielmo de Lorena's diving bell. In my opinion, this is the only plausible solution but it
remains a hypothesis nonetheless.
Guglielmo de Lorena and Francesco de Marchi certainly deserve credit for being the first
underwater archaeologists to use a diving apparatus and de Lorena probably deserves the credit
for inventing Halley's method two hundred years before the recognized inventor. To close the
loop, another amateur archaeologist, Annesio Fusconi, explored the ships of Lake Nemi in a
diving bell almost three hundred years later, in 1827. Fusconi used a Halley diving bell.
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Bibliography
Alberti, Leon Battista; I dieci libri de L' Architettura,; Vicenzo Vagaris, Venice 1546
Biondo, Flavio; Roma ristaurata et Italia illustrata; Domenico Giglio, Venice 1558
Francesco de Marchi, Architettura militare, Romanis, Rome 1810
Ucelli, Guido; Le Navi di Nemi; Instituto Poligrafico e Zecca dello Stato, 1950
Marx, Robert F.; The History of Underwater Exploration, Dover, 1990
NASA HIDH (Human Integration Design Handbook) NASA/SP-2010-3407, Appendix B:
Examples for Anthropometry, Biomechanics and Strength
NOAA (National Oceanic and Atmospheric Administration, U.S. Department of Commerce);
Diving Physiology
OSHA (Occupational Safety and Health Administration); Respiratory Protection Standard
29CFR1910.134
Speziale, G. C. The Roman Galleys in the Lake Nemi, Mariner's Mirror 15:4, 1929, 333-346
