If you study enough history of science, you learn that the things that scientists are most famous for are often not their only work of interest — or even the most fascinating thing they’ve done!  The significance of a scientist’s major discovery can overshadow and obscure things that are quite intriguing, and even more of an influence in contemporary times.  An obvious example of this is Albert Einstein: he’s known popularly for his work on the theory of relativity, but relatively few people outside of science are aware that he made important theoretical contributions to quantum mechanics and statistical mechanics, as well — all three in the same year, in fact!

A less familiar example is Sir Edmond Halley (1656-1742).  You most likely know him for Halley’s Comet!  He was not the discoverer of said comet, but was the first to recognize that the comet that appeared in 1682 must be the same object that had also been observed in 1531 and 1607 , and he predicted its return in another 76 years.  This prediction, based on Newton’s laws of gravity and motion, was vindicated in 1758 by the German farmer and astronomer Johann Georg Palitzsch.  Halley was in general a very successful astronomer, even becoming the second ever Astronomer Royal in Great Britain in 1720.

What you likely do not know about Halley, however, is that he spent extended periods of time deep underwater!  In volume 29 of the Philosophical Transactions, dated 1714-1716, Halley published the results of his experimentation in new ways to work comfortably underwater, titled suggestively: “The art of living under water”.  Halley’s work, in which he improved existing models of diving bells, turned out to be influential for years after its publication, and his techniques were implemented by many undersea laborers.

A diving bell is one of the oldest techniques for staying underwater for long periods of time.  In its simplest incarnation, it consists of a heavy inverted metal “bell” that is open in the bottom and traps air underneath it.  Provided the bell is heavy enough, its weight overcomes its buoyancy and it can be lowered to appreciable depths of water.

Such bells have been in use for a very, very long time; the Greek philosopher Aristotle (384 BCE — 322 BCE) included a reference to such a device in his Problems, in “Problems connected with the ears”*:

But there appears to be a spontaneous passage of the breath outwards; and we must next consider whether breathing inwards is so also.  Apparently it is; for they enable the divers to respire equally well by letting down a cauldron; for this does not fill with water, but retains the air, for it is forced down straight into the water; since, if it inclines at all from an upright position, the water flows in.

Other early accounts of diving bells include a legend that Alexander the Great descended into the depths of the Mediterranean in such a device.  The first well-documented use of a diving bell, however, did not take place until the Renaissance, and was for the surprisingly modern purpose of treasure-hunting!

Lake Nemi in Italy is a small lake of volcanic origin nestled some 19 miles south of Rome.  For years, fishermen had been catching strange artifacts in their nets — wood and bronze objects that evidently belonged to some sort of submerged structures.  In 1435, Cardinal Prospero Colonna, the owner of a pair of nearby castles, hired divers to investigate the lake’s depths.

What they discovered, and brought back up fragments of, were two pleasure barges of the Roman Emperor Caligula, though it would be much later before this identification was made.  The cost of operations, and the difficulty of diving to the lake’s depths, quickly brought the operation to a halt.

Precisely 100 years later, in 1535, a gentleman of Bologna named Captain Francesco de’ Marchi took up the exploration again, at this point evidently with an eye to actually raise the sunken vessels.  He brought with him Gugielmo da Lorena, who had constructed a sort of portable diving bell; this device was described in an 1839 magazine article** as follows:

This machine he states to have been a round tub-like vessel made of oak, two fingers thick, five palms long, and three wide, open at one end, and the other securely fastened; it was guarded with six hoops of iron, and at the open end or lower portion with one of lead, in order that it might sink easily; the outside was pitched and greased with tallow to make it water-tight; and it was provided with a thick piece of glass (set in so closely that the water could not possibly leak in), through which the person descending might see the objects in the water.  This instrument appears to have been placed over the head of the diver, who was supported by iron bands attached to the interior, which, clasping the shoulders, held him firmly, but allowed the use of his arms.  For greater security there was also attached a girth, which, descending down the back, passed between the legs, and was fastened in front by a buckle, which could be easily and speedily unclasped.

A 1909 Scientific American article*** gives an artist’s interpretation of what this device could have looked like:

Lorena’s design seems to have been forgotten due to his own desire to keep his invention secret, but within the next couple of centuries diving bells and other contrivances would be used to plumb the (relative) depths.  Here we can let Sir Edmund Halley take over the story, circa 1714 (keeping ye olde spelling, Capitalization, and emphasis):

There have been many Methods proposed, and Engines contrived, for enabling Men to abide a competent while under Water: And the Respiring fresh Air being found to be absolutely necessary to maintain Life in all that breath, several ways have been thought of, for carrying this Pabulum Vita down to the Diver, who must, without being somehow supplied therewith, return very soon, or perish.

We have heard of the Divers for Spunges in the Archipelago, helping themselves by carrying down Spunges dipt in Oyl in their Mouths: but considering how small a Quantity of Air can be supposed to be contained in the Pores or Interstices of a Spunge, and how much that little will be contracted by the Pressure of the incumbent Water, it cannot be believed that a Supply, by this means obtained, can long subsist a Diver.

This is an interesting idea, and one I had never heard of before!  Presumably, the “Oyl” on the sponge traps a small amount of air within it, and keeps the water out.  A diver can suck a small but potentially lifesaving amount of air out while underwater.  This idea has limits that Halley characterizes quite cleverly:

Since by Experiment it is found that a Gallon of Air, included in a Bladder, and by a Pipe reciprocally inspired and expired by the Lungs of a Man, will become unfit for any further Respiration, in little more than one Minute of Time; and though its Elasticity be but little altered, yet in passing the Lungs, it loses its vivifying Spirit, and is rendred effete, not unlike the Medium found in Damps, which is present Death to those that breath it; and which in an instant extinguishes the brightest Flame, or the shining of glowing Coals or red hot Iron, if put into it.

The term “damps” here refers to the poisonous air found in coal mines, of which there are many different types: black damp, after damp, fire damp, stink damp, white damp.  Black damps in particular consist of high concentrations of carbon dioxide, exactly the gas being produced by human respiration — Halley was being astute in making the connection.

I shall not go about to shew what it is the Air loses by being taken into the Lungs, or what it communicates to the Blood by the extream ramifications of the Aspera Arteria, so intimately interwoven with the Capillary Blood-Vessels; much less to explain how ’tis performed, since no discovery has yet been made, to prove that the ultimate Branches of the Veins and Arteries there, have any Anastomoses with those of the Trachea; as by the Microsope they are found to have one another.  But I rather choose to leave this Enquiry to the Curious Anatomist, to whom the Structure of the Lungs is better understood; and shall only conclude from the aforesaid Experiment, that a naked Diver, without a Spunge, may not be above a couple of Minutes enclosed in Water, (as I once saw a Florida-Indian at Bermudas) nor much longer with a Spunge, without Suffocating; and not near so long without great Use and Practice: ordinary Persons generally beginning to stifle in about half a Minute of Time.  Besides if the Depth be considerable, the pressure of the Water on the Vessels is found by Experience to make the Eyes Blood-shot, and frequently to occasion spitting of Blood.

In short, Halley notes that people can’t survive long unaided underwater!  Fortunately, other methods existed in his day for extended sojourns in the deep, but with their own limitations:

When therefore there has been occasion to continue long at the Bottom, some have contrived double flexible Pipes, to circulate Air down into a Cavity enclosing the Diver as with Armour, to bear off this pressure of the Water, and to give leave to his Breast to dilate upon Inspiration: the fresh Air being forced down by one of the Pipes with Bellowes or otherwise, and returning by the other of them; not unlike to an Artery and Vein.  This has indeed been found sufficient for small Depths, not exceeding twelve or fifteen Foot: but when the Depth surpasses three Fathoms, Experience teaches us that this Method becomes impracticible: for though the Pipes and the rest of the Apparatus may be contrived to perform their Office duly, yet the Water, its weight being now become considerable, does so closely embrace and clasp the Limbs that are bare, or covered with a flexible Covering, that it obstructs the Circulation of the Blood in them; and presses with so much force on all the Junctures, where the Armour is made tight with Leather, Skins or such like, that if there be the least defect in any of them, the whole Engine will instantly fill with Water, which will rush in with so much violence, as to endanger the Life of the Man below, who may be drown’d before he can be drawn up.  Upon both which accounts, the danger encreases with the Depth.  Besides a Man thus shut up in a weighty Cafe, as this must needs be, cannot but be very unwieldy and unactive, and therefore unfit to execute what he is designed to do at the Bottom.

The pressure of the water increases with depth, and is twice the atmospheric pressure at 30 feet.  In the scheme Halley describes above, the diver is connected by a hose to the surface, meaning the inside of the suit is at lower pressure than the outside, and any leaks will lead to a rapid and potentially fatal influx of water.  But what can be done, then, if one wants to explore deeper waters?

To remedy these Inconveniences, the Diving-Bell was next thought of; wherein the Diver is safely conveyed into any reasonable Depth, and may stay more or less time under Water, according as the Bell is of greater or lesser Capacity.  This is most conveniently made in form of a Truncate Cone, the smaller Basis being closed and the larger open; and ought to be so poized with Lead, and so suspended, that the Vessel may sink full of Air, with its greater or open Basis downwards, and as near as may be in a situation parallel to the Horizon, so as to close with the Surface of the Water all at once.

If it isn’t clear, a “truncate cone” is simply a cone whose top is sliced off at some level:

Under this Couvercle the Diver setting, sinks down together with the included Air into the Depth desired; and if the Cavity of the Vessel may contain a Tun of Water, a single Man may remain therein at least an Hour, without much inconvenience, at five or six Fathoms Deep.

A fathom is 6 feet, which means the diving bells of Halley’s time would be useful to about 36 feet.

But this included Air, as it descends lower, does contract itself according to the weight of the Water that compresses it: so as at thirty three Foot deep or thereabouts, the Bell will be half full of Water, the Pressure of it being then equal to that of the whole Atmosphere: and at all other Depths, the space occupied by the comprest Air in the upper part of the Bell, will be to the under part of its Capacity fill’d with Water, as thirty three Feet to the depth of the Surface of the Water in the Bell below the common Surface thereof.

As the water depth increases, the water pressure increases and it compresses the air in the diving bell.

And this condensed Air, being taken in with the Breath, soon insinuates itself into all the Cavities of the Body, and has no sensible effect, if the Bell be permitted to descend so slowly as to allow time for that purpose.

This is, in essence, an early description of problems involving compression/decompression. The bell has to be lowered slowly to allow the body to adjust to the significant change in atmospheric pressure.

The only inconvenience that attends it, is found in the Ears, within which there are Cavities opening only outwards, and that by Pores so small as not to give admission even to the Air itself, unless they be dilated and distended by a considerable Force.  Hence on the first descent of the Bell, a Pressure begins to be felt on each Ear, which by degrees grows painful, like as if a Quill were forcibly thrust into the Hole of the Ear; till at length, the force overcoming the Obstacle, that which constringes these Pores yields to the Pressure, and letting some condensed Air slip in, present Ease ensues.

Emphasis is mine!  Halley seems very specific about the ear pain one feels on descent: how does he know what a quill in the ear feels like??!!

Blogger’s interpretation of Sir Edmund Halley’s leisure time.

But the Bell descending still lower, the Pain is renewed, and again eased after the same manner.  On the contrary, when the Engine is drawn up again, the condensed Air finds a much easier Passage out of those Cavities, and even without Pain.  This Force on teh auditory Passages might possibly be suspected to be prejudicial to the Organs of Hearing, but that Experience teaches otherwise.  But what is more inconvenient in this Engine, is the Water entring into it, so as to contract the bulk of Air (according to the aforesaid Rule) into so small a space, as that it soon heats and becomes unfit for Respiration, for which reason it must be often drawn up to recruit it: and besides the Diver being almost covered with the Water thus entring into his Receptacle, will not be long able to endure the Cold thereof.

So Halley notes that there are two major problems with diving bells as they existed in his time.  First, the air needs to be replaced quite often, which requires the bell to be lifted out of the water, a cumbersome task for such a heavy device.  Second, the bell fills mostly with water as the air within is compressed, soaking and chilling the divers and requiring them to return to the surface anyway.  To deal with both of these problems, Halley concocted an ingenious modification to the traditional bell:

Being engaged in an Affair that required the Skill of continuing under Water, I found it necessary to obviate these Difficulties which attend the use of the common Diving-Bell, by inventing some means to convey Air down to it, whilst below; whereby not only the Air included therein, would be refresh’d and recruited, but also the Water wholly driven out, in whatever Depth it was.  This I effected by a Contrivance so easy, that it may be wondred it should not have been thought of sooner, and capable of furnishing Air at the bottom of the Sea in any quantity desired.  The description of my Apparatus, take as follows.

The Bell I made use of was of Wood, containing about 60 Cubick Foot in its Concavity, and was of the form of a Truncate-Cone, whose Diameter at Top was three Foot, and at Bottom five.  This I coated with Lead so heavy that it would sink empty, and I distributed the weight so about its bottom, that it would go down in a perpendicular Situation and no other.  In the Top, I fixed a strong but clear Glass, as a Window to let in the Light from above; and likewise a Cock to let out the hot Air that had been Breathed; and below, about a Yard under the Bell, I placed a Stage which hung by three Ropes, each of which was charged with about one Hundred Weight, to keep it steddy.  This Machine I suspended from the Mast of a Ship, by a Spritt which was sufficiently secured by Stays to the Mast-head, and was directed by Braces to carry it over-board clear of the Ship side, and to bring it again within-board as occasion required.

So the initial improvements Halley implemented were quite straightforward: a weighted stage hanging below the bell to keep it from tipping and spilling air, a window in the top to let light in, and a valve  (cock) to let out hot air.

The real innovation, however, was Halley’s method for supplying new air to the bell:

To supply Air to this Bell when under Water, I caused a couple of Barrels, of about 36 Gallons each, to be cased with Lead, so as to sink empty; each having a Bung-hole in its lowest Part to let in the Water, as the Air in them condensed on their descent; and to let it out again, when they were drawn up full from below.  And to a Hole in the uppermost Part of these Barrels I fixed a Leathern Trunk or Hose, well liquored with Bees-Wax and Oyl, and long enough to fall below the Bung-hole, being kept down by a Weight appended; so that the Air in the upper Part of the Barrels could not escape, unless the lower ends of these Hose were first lifted up.

The Air Barrels being thus prepared, I fitted them with Tackle proper to make them rise and fall alternately, after the manner of two Buckets in a Well; which was done with so much ease, that two Men, with less than half their Strength, could perform all the Labour required: and in their descent they were directed by Lines fastened to the under edge of the Bell, the which past through Rings placed on both sides the Leathern Hose in each Barrel; so that sliding down by those Lines, they came readily to the Hand of a Man, who stood on the Stage on purpose to receive them, and to take up the ends of the Hose into the Bell.  Through these Hose, as soon as their ends came above the Surface of the Water in the  Barrels, all the Air that was included in the upper parts of them was blown with great force into the Bell, whilst the Water entred at the Bung-holes below, and fill’d them…

What Halley had achieved was a technique for providing compressed air to the diving bell!  When the diving bell descends, it is filled with air at atmospheric pressure that is compressed by the pressure of the water at depth, thus resulting in a partially filled diving bell.  In order to force that water out of the bell, one needs to provide additional compressed air; there was no mechanical means to do so in Halley’s time, however.  Halley got around this by letting the water pressure compress the air in barrels, which act as miniature diving bells themselves!  When the end of the hose attached to the top of the barrel is lifted above it, the air is forced out by the water and into the diving bell.  By the use of multiple barrels over multiple trips, the bell can be completely filled with air.

This not only allowed for a dry diving bell, however; it also resulted in a steady supply of fresh air:

…and so soon as the Air of the one Barrel had been thus received; upon a signal given, That was drawn up, and at the same time the Other descended: and by an alternate Succession furnished Air to quick, and in so great Plenty, that I my self have been One of Five who have been together at the Bottom, in nine or ten Fathoms Water, for above an Hour and half at a time, without any sort of ill consequence: and I might have continued there as long as I pleased, for any thing that appeared to the contrary.

Remember that this is taking place in the early 1700s: five people spending an hour and a half underwater at a depth of some sixty feet!  Halley’s design allowed this time to be spent in relative, even surprising, comfort:

Besides the whole Cavity of the Bell was kept entirely free from Water, so that I sat on a Bench, whcih was diametrically placed near the Bottom, wholly drest with all my Cloaths on.  I only observed, that it was necessary to be let down gradually at first, as about 12 Foot at a time; and then to stop and drive out the Water that entred, by receiving three or four Barrels of fresh Air, before I descended further.  But being arrived at the Depth designed, I then let out as much of the hot Air that had been Breathed, as each Barrel would replenish with Cool, by means of the Cock at the Top of the Bell; through whose Aperture, though very small, the Air would rush with so much violence, as to make the Surface of the Sea boyle, and to cover it with a white Foam, notwithstanding the great weight of Water over us.

Thus I found I could do any thing that was required to be done just under us; and that, by taking off the Stage, I could, for a space as wide as the Circuit of the Bell, lay the Bottom of the Sea so far Dry, as not to be over-shoes thereon.  And by the Glass Window, so much Light was transmitted, that, when the Sea was clear, and especially when the Sun shone, I could see perfectly well to Write or Read, much more to fasten or lay hold on any thing under us, that was to be taken up.  And by the return of the Air-Barrels, I often sent up Orders, written with an Iron Pen on small Plates of Lead, directing how to move us from Place to Place as occasion required.  At other times when the Water was troubled and thick, it would be dark as Night below; but in such Case, I have been able to keep a Candle burning in the Bell as long as I pleas’d, notwithstanding the great expence of Air requisite to maintain Flame.

Wow.  With a constant supply of air, he was able to even have a light source in the diving bell!

Halley concludes his discussion with suggestions of how his new diving bell might be used, but also throws in a tantalizing extension of his ideas:

This I take to be an Invention applicable to various Uses; such as Fishing for Pearl, Diving for Coral, Spunges and the like, in far greater Depths than has hitherto been thought possible.  Also for the fitting and plaining of the Foundations of Moles, Bridges, etc.  upon Rocky Bottoms; and for the cleaning and scrubbing of Ships Bottoms when foul, in calm Weather at Sea.  But as I have no experience of these matters, I leave them to those that please to try.  I shall only intimate, that by an additional Contrivance, I have found it not impracticable for a Diver to go out of our Engine, to a good distance from it, the Air being conveyed to him with a continued Stream by small flexible Pipes; which Pipes may serve as a Clew to direct him back again, when he would return to the Bell. But of this perhaps more hereafter.

(Emphasis mine!)  A diver could walk along the bottom of the sea, using a hose to convey compressed air from the diving bell!  An illustration of the complete Halley system, with mobile diver, is shown below, from an 1822 book****:

Here is another depiction, via an 1839 encyclopedia^:

Halley’s device made a big splash (pardon the pun) amongst engineers and divers.  In 1732, for instance, a letter appeared^^ in the Philosophical Transactions by Mr. Martin Triewald, “Captain of Mechanics and Military Architect to His Swedish Majesty”, which lavishes praise on Halley’s design and suggests “small additions”:

Having the sole Privilege for diving on all the Coasts in the Baltic belonging to his Swedish Majesty, no Opportunity has been wanting to make sufficient Trials with the Diving Bell and Air Barrels in several Depths, according to the ingenious Improvement of that worthy Gentleman Dr. Edmund Halley, made in the Year 1716, but with some small Additions.

Experience has likewise convinc’d me, that no Invention built upon any other Principles than those of the Campana Urinatoria [diving bell], can be of Use in any considerable Depths; or that the Diver, in any other Invention whatever, can be a single Moment safe.  I will not, for Brevity-sake, mention the many Impediments that attend other Inventions, only that of a Water Armour, in which the Man is drowned in an Instant, when such a Machine receives the least Leak: Whereas Experience has shewn, that when such an Accident has happen’d to the Diving Bell, as to my Knowledge it did once, when the Diver was 12 Fathom under Water, and a pretty large Hole happen’d to be struck in the Bell, by a Boult of the Wreck he went upon, at which Time the Air rush’d out of the same with such Violence as astonish’d the Beholders by the excessive boiling on the Surface of the Water, fearing, not without Reason, that the Man in the Bell was drowned; but he clapped his Hand to the Hole or Leak, and gave a Sign to be haul’d up, which was done with all the Ease and Safety as if no Accident had happen’d to him, the Water having only risen about half a Foot into the Bell by this Leak.

Though modifications were made, Halley’s diving bell was still being recognized and employed an astonishing number of years later.  Remember the barges in the Lake of Nemi, and the attempts to explore and raise them?  From the Scientific American article*** of 1909, we are told:

Various attempts were made once more, in 1827, by one Annesio Fusconi, an engineer, who used Halley’s diving-bell; but the results were unsatisfactory.

We find that Halley’s diving bell was still being used and referred to in 1827, over a hundred years since Halley himself did his first experiments!

Halley’s scientific oeuvre is therefore a somewhat curious one.  His predictions on Halley’s comet, which he is most known for today, were only vindicated over a decade after his death.  However, his work on diving bells, used and lauded during his lifetime and a century afterward, is virtually unheard of today!  There is a lesson here about realizing that a scientist’s life and work is often much greater than those things that have made them famous.

But what ever happened at the Lake of Nemi?  The 1909 Scientific American article concludes pessimistically:

The day when these galleys of Caligula shall be brought to land will be veritably a red-letter day in the archaeological calendar; but, own both to their condition and the depth at which they lie, we may well doubt if that can ever take place.

In fact, the galleys were recovered, though in a completely different manner than expected!  In 1927 Benito Mussolini ordered the Lake of Nemi to be drained in order to reclaim the ships.  The process was not completed until October of 1932, but revealed astonishing ships that were much larger than thought possible by Roman construction.  The first ship (Prima Nave) was 230 ft long and 66 ft wide, while the second (Seconda Nave) was 240 ft long and 79 ft wide.

Nemi ship hull, c. 1930.  Note the figure in foreground for scale (source).

Unfortunately, the ships were destroyed during World War II on May 31, 1944 by fire, though the cause of the fire is uncertain.  An organization, Association Dianae Lacus, was founded in 1995 to rebuild the ships from existing plans made by the Italian Navy, but the project seems to be on hold.  Hopefully someone will continue it in the future, as the Nemi Ships, like Halley’s diving bell, are important parts of history that should not be forgotten.

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* Aristotle, Problems, Book XXXII.  It should be noted that the passage in question may have been written much later by someone other than Aristotle, as the Problems were likely assembled and written by multiple authors up to the sixth century CE.

** “Trajan’s palace in the lake of Nemi,” The Penny Magazine (1839), 23-24.  At this time the floating “palaces” were thought to have been built by the emperor Trajan.

*** St. Clair Baddeley, “Caligula’s galleys in the lake of Nemi,” Scientific American Supplement 1737 (1909), 249-251.

**** Curiosities for the Ingenious (Thomas Boys, Ludgate Hill, 1822, 2nd edition).

^ London Encyclopædia, vol. 7 (Thomas Tegg, London, 1839), p. 351.

^^ Martin Triewald, “Concerning an Improvement of the Diving Bell,” Phil. Trans. 39 (1735-36), 377-383.

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Edmond Halley (1714). The Art of Living under Water: Or, a Discourse concerning the Means of furnishing Air at the Bottom of the Sea, in any ordinary Depths Philosophical Transactions, 29, 492-499