In my last post we looked at the maritime experience that Halley had accumulated as a passenger, surveyor, and diver before receiving his commission as Paramore’s master and commander, and in this post we’ll examine his diving career more closely and take a look at my favourite thing about Halley – his diving suit!
Halley first wrote about a method for working underwater in 1689, proposing a mobile bell built upon four wheels. He discussed the effect that the weight and pressure of water had on a diver, and how water would compress air inside a bell, and rise higher as the bell descended. He suggested that if a way could be found to send air down to the bell, this would drive out the water and allow the diver – if wearing fishermen’s boots – to remain safe and dry inside. 
Robert Hooke was unimpressed, declaring Halley’s paper “the Same wth what I Shewed ye Society 25 years Since”, but diving and diving equipment have had a long and interesting history and probably neither Halley nor Hooke was quite as original as each believed himself to be, though Halley does deserve credit for being one of the few designers who went on to build a bell – and even to go down in it. 
His opportunity came during his involvement in the salvage operation on the “Guynie Friggott”, a Royal African Company ship which foundered on the south coast near Pagham around 1 April 1691, and from May of that year Halley was delivering regular reports of his activities to the Royal Society with escalating enthusiasm.
At the meeting on 26 August, he read a paper describing the bell he had built:
The Diving tub [a truncate cone] was made 5 foot at Bottom where it was open, 3 foot at top and 5 foot deep… and under the bell by three ropes I fastned a stage about 2½ foot below to stand on… Within the bell I placed a bench about a foot from the bottom for the men below to sitt on when they should be cold and where a man might sett with all his clouths at any depth drie. I made likewise in the top of the bell a window to let in the light which was very thick and strong but as clear glass as could be gotten, and I placed a small Cock in the same crown of the bell to let out the hot & effete air unfitt for further respiration. 
Halley reported that the deeper the bell sank, the higher the water rose within it, which he countered by his “principall invention” of adapting cask to be sent down filled with air, having a bunghole underneath through which water would enter, and a cock at the top (later a flexible tube) to release the compressed air when the cask was drawn into the bell and raised above water, thereby replenishing the bell’s air and lowering the level of the water.
By this means I have kept 3 men 1¾ [hours] under water and in ten fathoms deep without any the least inconvenience and in as perfect freedom to act as if they had been above.
That’s certainly impressive, but four weeks later Halley read another paper to the Society and this time he was so excited by his creation that he “desire[d] to conserve to my self the right of priority of Invention”: this was Halley’s diving suit.  But before we read his description, let’s take a look at a nineteenth-century illustration of his apparatus, which appeared in Rees’s Cyclopædia and is shown with the permission of the Science Museum:
There are several depictions of Halley’s diving bell on the internet but this is the closest to Halley’s description. You can see it’s a truncate cone built of wood with a weighted stage beneath, attached by three strong ropes to the bell. Inside is a bench with a man sat “drie” in his “clouths”, and in the roof on the right is a cock to release the “effete air unfitt for further respiration”. To the right is a cask, delivering fresh air to the bell, and to the left is the diver, wearing a not entirely convincing version of Halley’s diving attire, topped off with… but let’s hear the description of that contrivance from Halley:
A Man having a suite of Leather fitted to his body, with a cap of Maintenance… cappable to hold 5 or 6 gallons [of air]… must have a pipe coming from the Diving bell to his Capp, to bring him Air, which will be returned by another pipe, which must go from the cap of Maintenance, to a small [receptacle] of Air ?placed above the Diver into which it is to return the air, that has been breathed; whilest the other brings it to the man… 
Well that’s splendid, but what precisely did this cap of maintenance look like? Halley describes it as a “small vessell on the head of the diver which from its shape and use I call a capp of maintenance”, which is a little puzzling as caps of maintenance sit on top of the head but this presumably fitted over the head and was akin to a small bell, as imagined in the illustration above.  In which case, the device seems unlikely to pass any health and safety assessment, as when the diver bent down to retrieve something or if he tripped, the cap would presumably have tilted and flooded with water!
But that’s a trifling objection and Halley was rightly undaunted, describing his own triumphant descent in the same paper:
Having fortified my self against cold by a double or triple flannel or knit woolen westcoat and excluded the water by a well liquored leather suit made fitt and close to the body, I make my self considerably heavier than water by adding a girdle of ledon shott… with this the diver can descend easily to the Diving tubb… 
I love that detail about the waistcoat, it’s a rare evocation of Edmond’s physical presence and it brings his wife Mary to mind. Did she knit the waistcoat? Did she help with the design and fit of his suit? Alas, we know nothing of Mary’s role or her view of his projects, but we do know more about the liquored suit as Halley later described the recipe for his waterproofing oil to the Royal Society. Here’s the relevant minute:
Halley’s Liquor for his Leather Suites was said by him to consist of equall parts Bees wax, Tallow, Turpentine, and as much Train oyle [whale oil] as all the rest, dipping therein, when all is scalding hott. 
Notice it’s now “Leather Suites”, plural, and I’m assuming that’s because he’s producing them for other divers engaged in the operation, rather than enlarging his personal collection of niche-interest leatherwear. The suits seem to have been effective at keeping the divers dry and toasty as Halley – at least – was happy “to continu[e] there as long as I pleased”, while the glass window at the top admitted so much light into the bell that “I could see perfectly well to Write or Read” 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.” 
That was typical of Halley: when a subject caught his attention he explored it obsessively, and at Royal Society meetings throughout this period we find him reporting not just on improvements to his bell and attendant devices, but on the appearance of light below water, the strength of currents in streams, his experience of aural barotrauma (alleviated by “Oyle of Sweet Almonds”), and his idea for an instrument to measure the depth to which a diver had descended.
But it’s his diving suit that captured my own imagination: is it too fanciful to picture him donning his three waistcoats, his oiled leather suit, his fishermen’s boots, and his cap of maintenance, then lumbering downstairs to display himself to Mary, his servants and two young daughters? He must have been an impressive sight. Well, a sight, anyway.
UPDATE JUNE 2018
Wonder no more what Halley’s diving suit looked like, because since writing this post I’ve seen Halley’s own drawing of it, sketched on the back of the Royal Society minutes he was taking. You can see the suit for yourselves in this short ‘Objectivity’ video (which, alas, refers to him as ‘Sir Edmond’ – sigh).
 Royal Society, Halley Papers, Cl.P/21/28.
 Hooke, Diary, 6 March 1689, British Library, Sloane MS 4024. You can read a short history of diving here and here – or if you simply want to see a picture of Alexander the Great in a diving tub, enlarge the second image shown here.
 RS, Cl.P/21/38.
 RS, Cl.P/21/39.
 RS, Cl.P/21/40.
 RS Minutes, 9 June 1692, JBO/9 p88.
 Halley, ‘The Art of Living under Water…’, Phil Trans (1714) Vol 29 pp 492-499. Well worth a read!