Halley’s Atlantic Chart, part 2: his results

Halley undertook his Atlantic voyages to measure the magnetic variation at sea. Magnetic variation (or declination) is the angle between magnetic and geographic north in a horizontal plane. Halley thought that if a pattern could be observed in the variation, it might offer a way to determine a ship’s longitude at sea. He measured the variation regularly throughout his two voyages and began preparing the presentation of his data as soon as he arrived back in Deptford in September 1700.

Halley is noted for his ability to draw general conclusions from complex data and for his appreciation of visual representation of those conclusions, and he demonstrated both these traits in presenting his data in the form of a sea chart.

The chart – known as his Atlantic Chart – holds an important place in the history of cartography, as it is regarded as the first published chart to represent magnetic declination using what became known as isogonic lines. It was not the first time such lines had been thought of, but the earlier examples were never published and Halley is thought unlikely to have known about them. [1]

We’ll look at the chart and its data in a moment, but first I’d like to highlight some of its decorative features.

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To the east of the mysterious birds, we find The Icey Sea with the black-streaked “Mountains of Ice” that Halley and his crew had encountered in February (notice their track passing through it). Neither Halley nor his crew had seen icebergs before and Halley was unsure whether they were floating or grounded.

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The track of Halley’s second voyage is shown on the chart and indicated by representations of the Paramore pursuing her figure-of-eight course.

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There are three cartouches on the chart: the one on South America is formed by a native family reclining beneath two fruit-laden palm trees. The adults wear feathered headdresses and skirts, the woman clutches a small child and the man holds a spear, has a bow at his feet and a quiver of arrows on his back. Behind them, hanging between the trees, is a sheet bearing the chart’s title:

A New and Correct CHART Shewing the Variations of the COMPASs in the WESTERN & SOUTHERN OCEANS as Observed in ye Year 1700 by his Ma:ties Command by Edm. Halley.

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A second cartouche appears on the landmass of Africa and carries the chart’s dedication to William III and is topped by personifications of astronomy (holding a telescope and armillary sphere), navigation (a backstaff and ship) and mathematics (dividers and triangle).

The third cartouche is found on North America and explains the information depicted in the chart:

The Curve Lines which are drawn over the Seas in this Chart, do shew at one View all the places where the Variation of the Compass is the same; The Numbers to them, shew how many degrees the Needle declines either Eastwards or Westwards from the true North; and the Double Line passing near Bermudas and the Cape de Virde Isles is that where the Needle stands true, without Variation.

And here’s the full chart, shown with the permission of the Royal Geographical Society:

Halley's Atlantic Chart (© Royal Geographical Society (with IBG), Image S)

Halley’s Atlantic Chart – click to open in a new tab. (© Royal Geographical Society (with IBG) (£), Image S0015919)

You can see that it has two compass roses, the one in the mid-Atlantic radiating lines that somewhat obscure Halley’s “Curve Lines” of equal magnetic declination. (Halley himself realised this was a problem and omitted this feature on the World Chart he published around a year later.) It is on a Mercator projection, with lines of latitude and longitude, and the meridian of London, the equator and tropics identified, but no indication of scale.

This version of the chart includes text that was written subsequently by Halley and printed in two strips that could be stuck to the sides of the original chart. It describes how to consult the chart by way of examples, and explains that it has two uses:

  • to enable the mariner to know by how much he needs to adjust his course to take account of the magnetic variation, and
  • to estimate a ship’s longitude at sea, the curve lines running nearly north-south (as off the west cost of Africa) giving “a very good Indication of the Distance of the Land” from the ship

This useful knowledge is obtained by reference to the isogonic lines. They are a little difficult to pick out but you can easily see the double curved line to the right of the central compass, which Halley has named The Line of No Variation (the agonic line) and the curved lines above and right show the degree to which the compass varies west of geographic north, and to the left, east of geographic north (the number of degrees of variation is shown on the horizontal line above The Icey Sea).

As mentioned above, the chart was (and is) regarded as the first (extant) published use of isolines (contour lines), and until the nineteenth century these lines were known as Halleyan lines.

So the chart is impressive and historically important, but how accurate was it? Alan Cook observed that it was “an improvement on anything that had gone before”, [2] but as I wrote in a previous post, the problem with longitude is knowing both where you are and where the place is that you’re heading. Halley’s recorded longitude was often inaccurate and sometimes considerably so: when he was sailing towards St Helena from the east, the longitude value he reported is actually west of the island – and so the degree of variation he thought applied to the east of the island in fact applied to the west.

Similarly the coordinates of islands and land weren’t then accurately known: Cape Horn, for example, is roughly 10° further west on Halley’s chart than we now know it to be, so his lines of variation near that coast must be likewise misplaced. [3] It seems to me that the moral of this exercise is that to devise a chart that helps estimate a ship’s longitude at sea, the deviser needs to have a fairly accurate knowledge of longitude in the first place.

But Halley was alert to the likelihood of error in his chart and in his final paragraph he wrote that:

…all knowing Mariners are desired to lend their Assistance and Informations, towards the perfecting of this useful Work. And if by undoubted Observations it be found in any Part defective, the Notes of it will be received with all grateful Acknowledgment, and the Chart corrected accordingly.

And I think that’s how Halley’s chart was most useful: it was a cartographic innovation from which better and more accurate maps might evolve.

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[1] For details of prior manuscript isoline charts see Thrower, The Three Voyages of Edmond Halley in the Paramore 1698-1701 (Hakluyt Society: London, 1981) pp 57-58, and Thrower, Maps & Civilization (3rd ed, Chicago and London, 2008) pp 97-101.

[2] Cook, Edmond Halley: Charting the Heavens and the Seas (Oxford, 1998) p 281.

[3] In 1714 Halley defended his World Chart (an extended version of his Atlantic Chart, incorporating data supplied by others) in the Philosophical Transactions from charges of inaccuracy by the French Royal Academy of Sciences, including that he had placed Cape Horn too far west.

All images © Royal Geographic Society (with IBG) (£), Ref S0015919.

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Halley and longitude

If you’ve been following this blog about Halley’s voyages, you’re probably aware that 2014 is the 300th anniversary of the Longitude Act, which offered financial rewards for practicable methods of finding longitude at sea to specified degrees of accuracy.

Halley was involved with the quest for longitude throughout his long life: in 1675, aged 18, he was present when Flamsteed and Hooke visited the proposed site of the new observatory in Greenwich, being built by order of Charles II to help find longitude at sea; he was made a commissioner under the 1714 Longitude Act, courtesy of his position as Savilian Professor of Geometry (later also as Astronomer Royal), and around 1730 it was Halley who sent clockmaker John Harrison to see George Graham to discuss his ideas for a marine chronometer.

By the second half of the 18th century, there were two serious contending methods for finding longitude at sea, lunar distances and timekeepers, but in the late 17th and early 18th centuries, a diverse range of schemes were proposed, including finding longitude via magnetic variation.

Magnetic variation (or declination), the angle between magnetic and true north in a horizontal plane, was well known to the scientifically-minded, as too was the fact that it varied in different locations and also over time. It was thought that if an underlying pattern to the variation could be identified, it might offer a way of finding one’s longitude – and it was this that Halley was seeking to do on his voyage.

We’ll see Halley’s results in due course but for now we’ll consider one of the key difficulties with the theory, which is best illustrated by comparing data from four ships’ logs. [1]

At the start of Halley’s first voyage, he sailed from the Isle of Wight to Madeira in company with Admiral Benbow’s squadron and four of the five ships’ logs have survived, so we can compare their recorded latitude and longitude over several days:

COMPARISON OF LATITUDES AT NOON

1698 Falmouth Gloucester Lynn Paramore
Dec 2 47°28′ 47°39′ 47°24′ 47°23′
Dec 3… 46.28 46.30 46.13 46.20
Dec 14 32.39 32.36 32.43 32.25
Dec 15 32.22 32.26 32.19 32.15

Here, I’m showing the first and last two days that all four ships recorded data (leaving the English Channel and approaching Madeira) and you can see immediately that the latitudes are very similar – but the reported longitudes present a very different picture (first/last 5 days):

COMPARISON OF LONGITUDES AT NOON

1698 Falmouth Gloucester Lynn Paramore
Dec 2 149.3 8°01′ 2°10′ W 8°00′
Dec 3 60.1 6.59 3.30 9.10
Dec 4 5.53 5.12 10.03
Dec 5 29.9 5.34 6.00 10.09
Dec 6… 51′-5/10 4.27 7.07 11.07
Dec 11 8.41 W 3.00 9.35 12.15
Dec 12 8.55 W 3.00 9.39 12.15
Dec 13 10.50 1.08 11.15 14.09
Dec 14 12.03 0.14 11.42 15.03
Dec 15 13.20 13.11 16.07

This table looks like a confused jumble, demonstrating that this is a problematic coordinate. Looking first at the Paramore, Halley always noted that his longitude position was measured west from London, and on December 15 he described himself as being to the south-east of Madeira, which is 16°55′ west of London, and so 16°07′ seems a respectable figure for his position.

The Gloucester does not specify where its longitude is measured from but apparently starts from the same longitude as the Paramore but then declines in value to zero as it approaches Madeira, and so that ship’s longitude is being measured east from Madeira (or possibly El Hierro in the Canaries, a common zero meridian of the time, in which case the final value is over a degree out).

The Lynn‘s figures increase like the Paramore‘s, but the values are quite different and I think these values are measured from Lizard Point as they depart from the English Channel (it isn’t specified). The later values for the Falmouth are similar to the Lynn‘s but the earlier ones are unlike any others and I’m assuming these positions are only partially calculated and represent the minutes travelled since the previous noon.

So these logs demonstrate one of the problems with longitude: even if you could accurately measure your longitude, where did you measure it from? (The prime meridian at Greenwich wasn’t agreed upon until the 1880s.) And how did this varying data affect the accuracy of the period’s maps and charts?

In other words, Halley didn’t really know where he was (his recorded longitude is often erroneous, sometimes considerably so) or even, strictly, where he was heading as many places were wrongly laid down in maps – and so how useful could a theory be that was founded on wrongly-placed locations?

In spite of this, Halley apparently found all the islands he states he will sail for, even though some are little more than large rocks in a vast ocean. Halley followed the customary practice of parallel sailing (sailing along a coast until you attained the latitude of the place you were aiming for and then sailing east/west until you reached it) but on his “Southern cruise” he was seeking tiny islands (Tristan da Cunha, Martim Vaz) from the middle of the Atlantic ocean – I think he must have had at least one very sharp-sighted crew member on board!

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[1] References for the logs are: Falmouth NA, ADM 51/341; Gloucester NA, ADM 51/401; Lynn NA, ADM 51/3892; Paramore BL, Add MSS 30398. The figures are (mostly) degrees/minutes but the notation differs in each log (I’ve used the Paramore‘s).

Halley writes from Bermuda

The Paramore anchored in St George’s Harbour, Bermuda, on Friday 21 June 1700 and Halley and his crew remained there for nearly three weeks. They were busy during that time, the crew careening the ship in order to clean her, and Halley taking the latitude and longitude of the island, observing the tides and coastal dangers, and buying a new stream anchor to replace the one they had lost at Barbados.

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Bermuda, C17 (Wikimedia Commons)

Before leaving the island on 11 July, Halley wrote an informative letter to the Admiralty in London, describing his progress during the last few months:

(Halley to ?Burchett, dated 8 July 1700 from “Bermudas”, National Archives ADM 1/1871 (not autograph))

Honourd Sr

My last from St: Hellena, gave your Honour an Account of my Southern cruise, wherin I endeavoured to see the bounds of this Ocean on that side, but in Lattd. of 52°½ was intercepted with Ice cold and foggs Scarce credible at that time of the Year. haveing spent a Month to the Southwards of 40 degrees, and Winter comeing on, I stood to the Norwards Again and fell with the three Islands of Tristan da Cunha which yeilding us noe hope of refreshment, I went to St: Helena, where the continued rains, made the water soe thick with a brackish mudd, that when it settled it was scarce fitt to be drunke; all other necesarys that Island furnishes a Bundantley. at Trinidad we found excellent good water, but nothing else. Soe here I changed as much of my St Hellena water as I could, and proceeded to Fernambouc in Brassile, being desirous to hear if all were at peace in Europe, haveing had noe sort of Advice for near eight months, here one Mr. Hardwyck that calls himselfe English consull, shewed himselfe very desirous to make prize of me, as a pyrate and kept me under a guard in his house, whilst he went A Board to examine, notwithstanding I shewed him both my commisions and the smallness of my force for such a purpose, from hence in sixteen days I arrived at Barbados on the 21st of May, where I found the Island afflicted with a Severe pestilentiall dissease, which scarce spares any one and had it been as mortall as common would in a great measure have Depeopled the Island, I staied theire but three days, yet my selfe and many of my men were seazed with it, and tho it used me gently and I was soon up again yet it cost me my skin, my ships company by the extraordenary care of my Doctor all did well of it, and at present we are a very healthy ship: to morrow I goe from hence to coast alongst the North America and hope to waite on their Lordsps: my selfe within a month after the arrivall of this, being in great hopes, that the account I bring them of the variations and other matters may appear soe much for the publick benefitt as to give their Lordsps. intire satisfaction:

I am Your Hon:rs most

Obed:t Servant:

Edmond Halley

We’ve looked before at Halley’s encounter with icebergs, his stay on St Helena and his visit to Trinidad (modern Trindade), and read how Halley himself described being environed by “Islands of Ice” in the South Atlantic, but we can look now at some additional information concerning his arrest at Pernambuco and his illness at Barbados.

During his stay at Pernambuco Halley recorded In his logbook that:

Mr. Hardwick…desired me to call on him at his house this afternoon, where instead of Business he caused me to be Arrested, and a Portuguese Guard Sett over me … and I was given to understand that Mr. Hardwick had Acted in my Affair wth.out Authority being only impower’d to Act for the Affrican Company, and the Owners of the Shipp Hanniball wch. had been seized there as a Pirate and had no Commission of Consul

This “Mr. Hardwick” was one Joseph Hardwick who held the title of vice-consul in the city of Lisbon, from where the British envoy extraordinary, Paul Methuen, had given him authority to sail to Pernambuco “in Order to the takeing posession and remitting hither whatsoever remains there belonging to the ships Hanniball and Eagle which were Seized there last year [1697] by the Governours Order”. [1]

I haven’t had time to uncover the full story of the seizure of these ships but I noticed that Hardwick was specifically warned not to exceed his written authority, and so unless that authority had been extended in the two intervening years, I think that Halley was right to object that “Mr. Hardwick had Acted in my Affair wth.out Authority”.

The pestilential disease contracted by Halley and some of his crew at Barbados has not been identified, but a gastro-intestinal illness, yellow fever, and typhoid fever have all been proposed, the latter suggested by Halley’s remark in this letter that it “cost me my skin”. It’s interesting that he says that “it used me gently and I was soon up again”, because his log entries show that he was ill for quite some time, falling ill on 24 May and remarking that his strength was returning “but Slowly” on 5 June, which sounds like a lengthy illness to me. [2]

His doctor on both voyages was George Alfrey, whom Halley seems to have known before the first voyage as he specifically requested that the Admiralty warrant Alfrey to be his “Chirurgeon”, observing that Alfrey had “served in severall of his Ma:ties shipps for some years last past.” [3] And though not a fellow of the Royal Society himself, Alfrey apparently knew some of the fellows as he was in communication (as we shall see) with Hans Sloane and James Petiver. It’s possible that Alfrey died less than three years after this voyage ended, as there’s a George Alfrey, “Chirurgeon of Woolwich”, who died in 1703. I’m not sure it’s the same man, but two surgeons named George Alfrey in a maritime location seems fairly unlikely. [4]

In any event, Halley’s belief in Alfrey’s abilities seems to have been well-judged and it’s pleasing to read that “we are a very healthy ship” as Halley and his crew prepare for the homeward passage to England.

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[1] Instructions to Joseph Hardwick, dated Lisbon 7 Feb 1698, National Archives, SP 89/17 Part 2, ff273r-27v.

[2] Norman Thrower mistranscribes this as “tho it used me greatly”, but the word is definitely “gently”. See Thrower, The Three Voyages of Edmond Halley in the Paramore 1698-1701, (Hakluyt Society: London, 1980) p 308.

[3] Halley to the Lords of the Admiralty, 21 Sept 1698, National Archives, ADM 106/519/365.

[4] The contents of the will of the George Alfrey who died in 1703 (NA PROB 11/471/222) don’t settle whether he was/was not Halley’s doctor and I have some slight doubt that it’s the same man as this one may only have been 22 at the start of Halley’s first voyage, which seems rather young for a surgeon who had served for “some years last past”.

Halley writes from St Helena

Before leaving St Helena, Halley sent a letter to the Admiralty – there’s no addressee but it’s presumably the Secretary, Josiah Burchett. He tells Burchett about the great danger they encountered among the “Islands of Ice” and also that he has “noe reason to doubt” that he will be able to derive a general theory of compass variation from his observations that will help mariners find their longitude at sea.

The letter isn’t in Halley’s handwriting, and I’ve made some minor changes to the punctuation and split it into two paragraphs to make it easier to read, but left the spelling as written.

(Halley to ?Burchett, dated 30 March 1700 from St Helena, National Archives ADM 1/1871)

Hono:rd Sr

I must Intreat You to lay before the Lords of the Admty this account of what I have done in execution of the Orders I Received from them. Since my last from St. Iago, which I hope came long since to Your hands, haveing not been able to fetch Madera by reason of the winds shifting upon me, I was Obleged to putt into Ryo Jennero in Brasile to gett some Rumm for my ships company, from whence I wrote you a letter which I suppose will not be in Engl[and] soe soon as this. I left Ryo Jennero on the 29° of December last and stood to the Southward till the 1st of February, when being gotten into my Station Vizt in Lattd: 52°½ and 35° west Longitude from London, we fell in with great Islands of Ice, of soe Incredible a hight and Magnitude, that I scarce dare write my thoughts of it. At first we took it for land with chaulky clifts, and the topp all covered with snow, but we soon found our mistake by standing in with it, and that it was nothing but Ice, though it could not be less then ?200 foot high, and one Island at least 5 mile in front. We could not get ground in 140 fadtham, Yet I conceive it was a ground, Ice being very little lighter then water and not above an Eight part above the Surface when it swims. It was then the hight of Summer, but we had noe other singe of it but long Days; it froze both night and day, whence it may be Understood how these bodies of Ice are generated being allways increased and never thawing.

The next day February the 2d. we were in Imminent Danger to looss our ship and lives, being Invironed with Ice on all sides in a fogg soe thick, that we could not see it till was ready to strike against it, and had it blowne hard it had scarce been possible to escape it: Soe I stood to the Northward to get clear of it, which in the Lattd. of 50° I did, and their Saw the last Ice. In my way hither I Discoverd* the Isles of Tristan da Cunha, and in Eleaven Weeks from Ryo Jennero I arrived at this Island, to fill my Water and refrezen my men, and in this whole course I have found noe reason to doubt of an exact conformity in the variations of the compass to a generall Theory, which I am in great hopes to settle effectually

I am

Honord Sr.

Your most Obedt Servt

Edmond Halley

* “Discoverd” here simply means ‘saw’

Halley’s second logbook

First, apologies for the lengthy gap since my last post; I’ve been unwell but the skill of the ship’s chirurgeon has got me back on deck and scampering up the rigging with the best of ’em.

That’s me, but what about Halley? Well, he’s been sailing steadily southwards (well, SSE) since leaving St Iago (Santiago) in the Cape Verde Islands and reached Rio de Janeiro on December 14, where he’ll stay for two weeks. This section of his voyage, down to his most southerly latitude (which he’ll reach about the end of January), isn’t very eventful and so I thought this was a suitable time to take a look at his second logbook, which begins with this heading:

A Journal of a Voyage in his Ma:tis Pink ye Paramore intended for the Discovery of ye Variation of the Compass kept by Edmund Halley Commander anno 1699 & 1700

(I’ve written before about the correct spelling of Halley’s first name and that of his ship.)

Like the first logbook, the second is not written by Halley but presumably by his clerk, William Curtiss, and so again the spelling and abbreviations are the clerk’s and not Halley’s. The log is written on the same size (roughly 41cm high by 27cm wide) and type of paper as the first logbook and covers 53 sides (the first was 17 sides).

Unlike the first journal, the second is not signed at the end by Halley and it also differs slightly in structure. The first log included several tables of data, ranging from two days to forty-three, but the second has only two tables of eight and eleven days, and instead largely gives the data in prose, as in these two examples for 2 and 11 November 1699:

[2 Nov] By a very good observation I am in 7°.40′ North Latt: Since yesterday noon we have had the Winds from EbN to NEbE a fine gentle Gale; in the night we had much Lightning, but no Thunder. We have made our way S24°E Distance 73 Miles, Diffrence of Longitude 30′ East, My Long from Lon: 18°:57′ West

[11 Nov] By a good observation I am in Latt 2°.42′ We have had the wind mostly at SSE and have made our way good W38S. 62 Miles diffr of Long 48 Minutes Long West from Lon. 20°:37′ a Fine Gale and fair weather Saturday Morning and Evening I had a good observation of the Variation Morn Ampl[itude] 18°:50′ Even 21°:30′.

So at noon each day he records his latitude, the weather, his course, miles covered, difference of longitude from the previous day’s measurement, and his total longitude west from London. Most entries at sea include this basic information in this style, and a number of days include additional data (variation and amplitude) and anything out of the ordinary (such as birds flying around the ship). I’m rarely tweeting a full entry, usually the latitude, weather and any general information. I’ve also occasionally silently added some punctuation and have always rendered values as DD°MM’ regardless of how they appear in the log.

There is no overall ‘story’ to the second voyage, unlike the first with the hostility and court martial of Lieutenant Harrison. Halley is now focused on collecting his data and we’ll see what use he puts it to at the end of his voyage.

One thing I find surprising (and frustrating) is that he makes very few remarks about the places he visits and appears to show little interest in the lands or native inhabitants – and this leads me to wonder whether Halley might perhaps have kept a private journal?

His second logbook is very much a ship’s log rather than a natural philosopher’s journal, but as an active member of the Royal Society I would expect him to take an interest in a far wider range of topics with which he might entertain the Fellows on his return. [1] When Halley was at the Chester Mint, in the two years before his first voyage, he sent several reports back to the Society (a number of which were published in the Philosophical Transactions), so it seems strange that he would sail around the Atlantic and not make notes of events that would be likely to interest the Fellows. [2]

I haven’t encountered any suggestion of a private journal but we saw from the Society’s minutes that he collected botanical specimens on his first voyage, which was not indicated in his logbook, and there are similarly some unreported items that will appear at the end of this voyage, so a private journal or notes might perhaps have existed – and how much more interesting that would surely be for the general reader!

But there are some entertaining entries still to come in his official logbook, which will resume on 29 December when he leaves Rio for the southern latitudes and he and his crew encounter something none of them have ever seen before…

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[1] Halley was elected Fellow of the Royal Society on 30 November 1678 but had to resign his fellowship when he became clerk in January 1686. He was re-elected FRS on 30 November 1700.

[2] These accounts from Chester published in the Phil Trans give some idea of the range of subjects Halley might report on: a dog born “per anum” and a Roman altar; two reports of a hailstorm here and here; a trip to Wales to try the Torricellian experiment; observations of a lunar eclipse.

Instructions for Halley’s second voyage

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Halley received his commission to be Master and Commander of Paramore on his second voyage on 23 August 1699, and his instructions for the voyage on the 12 September.

His instructions were almost identical to those he received for his first voyage, namely:

  • to measure the variations of the compass (magnetic variation)
  • to ascertain the latitude and longitude of the places he visits, particularly in the West Indies
  • to discover the unknown lands in the south Atlantic

only this time, the section on the Terra Incognita refers to finding it specifically between the latitudes of 50 and 55 degrees south, which Halley himself asked to be included in his instructions in a letter to the Admiralty.

Here are his instructions in full (remember ye/ym = the/them):

Whereas his Majesty has been pleased to lend his Pink ye Paramour, for your proceeding a second time w:th her on an Expedition to Improve ye knowledge of the Longitude & variation of ye Compass, which ship is now Compleatly mann’d, stored and victualled at his Majesty’s Charge for ye said Expedition, you are therefore hereby required and directed forthwith to proceed with her according to ye following Instructions.

You are without loss of time to Sett Saile with her, and proceed to make a Discovery of ye unknowne South lands between ye Magellan Streights & ye Cape of good hope, between ye Latt:d of 50 & 55 South, if you meete not with ye land sooner observing ye variation of ye Compass with all ye accuracy you can, as also ye True Scituation both in Longitude & Latt:d of ye ports where you arrive.

You are likewise to make ye like observations at as many of ye Islands, in ye Seas between ye aforesaid Coasts, as you can (without too much deviation) bring into your Course.

In your returne home you are to visit ye English West India Plantations, or as many of ym as conveniently you may, & in them to make such observations as may contribute to lay them downe Truly in their Geographicall Scituation, & in all ye Course of your Voyage, you must be carefull to omitt no oppertunity of noting ye variation of ye Compass, of which you are to keep a Register in your Journall.

You are for ye better lengthning out your provisions, to put ye Men under your Comand, when you come out of ye Channell, to six to four Men’s allowance assuring ym that they shall be punctually paid for ye same at ye End of ye Voyage.

You are during ye Terme of this Voyage, to be very carefull in Conforming your selfe to what is directed by ye Generall printed Instructions annexed to your Comission, with regard as well to his Majesty’s honour as to ye Governement of ye ship under your Comand; and when you returne to England, you are to call in at Plymouth, & finding no orders there to ye contrary, to make ye best of your way to ye Downes & remaine there till further order.

Cape Horn is roughly on the same latitude that Halley's headed for (via Wikipedia Commons)

Cape Horn is roughly on the same latitude that Halley’s heading for (via Wikimedia Commons)

The end of Halley’s first voyage

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Extract from Halley’s first logbook, in another hand but with his signature (© British Library (£), Add MSS 30368, f.8v)

“The Gunns and Gunners Stores were delivered to the Tower Officers and that Same Evening we moord our Shipp at Deptford”

This was the final entry dictated by Captain Halley to his clerk on Tuesday 11 July 1699, with Halley’s own signature bringing the log of his first voyage to a close.

Halley was paid wages of £168 0s 0d, less deductions for the Royal Hospital for Seamen at Greenwich and for “bearing Supernumery’s”, leaving net pay of £140 2s 8d. Lieutenant Harrison received £71 5s 2d (£71 0s 0d net), and the clerk Caleb Harmon was paid £15 19s 3d (£15 3s 1d net), which his father apparently collected.

The pay book was signed by both Halley and Harrison:

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Extract from the Pay Book (© National Archives (£), ADM 33/196)

There was one final page to Halley’s logbook: “A Table of the true Latitudes & Longitudes of the Severall Islands and Ports mentioned to have been seen in this Voyage”, and I’ve adapted that table for inclusion below.

Otherwise, Halley will spend the next few weeks persuading “their Lopps” to allow him a second voyage in Paramore – and he’ll set sail again in mid-September when this blog and his twitter feed (@HalleysLog) will resume.

I hope you’ll join us again in September, when we’ll start by looking at what Halley got up to over the summer – in the meantime, I wish all our readers a great summer!

Halley’s table of latitudes and longitudes

I’ve separated Halley’s table into two parts – one for latitude and one for longitude – so that I could add modern values for comparison with Halley’s. The modern values are taken from Wikipedia and may not represent the exact same location where Halley made his own observations, and so the figures and differences are indicative only (I haven’t noted whether the differences are plus/minus to keep things simple). 1 degree of latitude is roughly equal to 69 miles (approx 111 km), and 1 degree of longitude is also about 69 miles at the equator, but lessens as you approach the poles.

In both tables, the place names and ‘Halley’ column are taken from the table that concluded Halley’s logbook, but the values there are not always the same as those he recorded during the voyage. For example, the longitude values he recorded during the E-W Atlantic crossing were significantly in error – undoubtedly owing to his inexperience in reading the currents – but he realised this on reaching Brazil (via astronomical observations) and so recalculated his longitude values for the final table. (Harrison seems to have recorded more accurate values during this passage.)

As you’d expect, his latitude values are more accurate than his (amended) longitude values, although his longitude values around the Caribbean seem pretty good. Longitude is measured West from London.

Table 1 – LATITUDE

 

HALLEY

MODERN

DIFF

The Lizard

49°54′

50°02′

0°08′

North part of Scilley

49°57′

49°56′

0°01′

Madera

32°30′

32°39′

0°09′

Isle of Sall

16°10′

16°36′

0°26′

St Iago ye North Cape

15°18′

15°17′

0°01′

Isle of May

15°05′

15°14′

0°09′

Porto praya South side of St Iago

14°50′

14°55′

0°05′

Fernando Loranho

3°57’S

3°51’S

0°06′

Cape Dello at the Mouth of ye River of paraiba in Brasill

7°00’S

6°58’S

0°02′

Barbadoes

13°10′

13°10′

0

Martinica

14°35′

14°40′

0°05′

Desseada

16°23′

16°19′

0°04′

Antegoa

17°10′

17°05′

0°05′

Monte serrat North end

16°50′

16°45′

0°05′

Redando

17°[0]2′

16°56′

0°06′

Nevis Road

17°15′

17°09′

0°06′

Old Road of St Christophers

17°30′

17°18′

0°12′

Eustachia

17°36′

17°29′

0°07′

Saba

17°42′

17°38′

0°04′

St Bartholomew

17°55′

17°54′

0°01′

St Martins

18°05′

18°04′

0°01′

Anguilla

18°15′

18°23′

0°08′

Table 2 – LONGITUDE

 

HALLEY

MODERN

DIFF

The Lizard

5°30′

5°11′

0°19′

North part of Scilley

7°10′

6°19′

0°51′

Madera

16°45′

16°55′

0°10′

Isle of Sall

22°00′

22°54′

0°54′

St Iago ye North Cape

22°40′

23°45′

1°05′

Isle of May

22°00′

23°10′

1°10′

Porto praya South side of St Iago

22°30′

23°31′

1°01′

Fernando Loranho

34°00′

32°25′

1°35′

Cape Dello at the Mouth of ye River of paraiba in Brasill

36°00′

34°50′

1°10′

Barbadoes

59°05′

59°33′

0°28′

Martinica

60°20′

61°00′

0°40′

Desseada

60°30′

61°03′

0°33′

Antegoa

61°27′

61°48′

0°21′

Monte serrat North end

61°47′

62°12′

0°25′

Redando

61°55′

62°20′

0°25′

Nevis Road

62°10′

62°35′

0°25′

Old Road of St Christophers

62°25′

62°44′

0°19′

Eustachia

62°40′

62°58′

0°18′

Saba

62°55′

63°14′

0°19′

St Bartholomew

62°35′

62°50′

0°15′

St Martins

62°50′

63°03′

0°13′

Anguilla

62°50′

63°05′

0°15′