The Council had decided that they should turn east, and in doing so they had avoided potential disaster.
“At noon we directed our course to eastward with a north-north-westerly wind and a top-gallant gale; our estimated latitude being 45° 47′, and Longitude 89° 44′; course kept south-south-east sailed 17 miles.”
Having just avoided the French Southern and Antarctic lands they ran eastwards for three days, before again turning south-east.
The foul weather and intermittent fog persisted, as did sightings of weed on the water, and at the latitude 49°S Tasman recorded that
The weather was so bad that it was impossible to convene the Council. However, they passed messages in a small barrel between the ships.
On Nov 7th, Visscher, the Pilot Major delivered some extraordinary news… the Company’s understanding that the Solomon Islands reached as far as 220°E was certainly incorrect, and could not be relied on. On board the Zeehaen, Visscher had a globe of the world, and a map… and disagreed very significantly on the longitude of the Solomon Islands. On close inspection Visscher discovered that they had different origins for longitude.
The VOC used the convention that zero longitude, the meridian, was measured from the Peak of Tenerife. This was the coordinate system in their map, “the large chart of the South Sea”, the map drawn by Gerritsz showing all the known lands in Australia.
However, the globe was an older device, and had a different meridian.
“The terrestrial globe shows us that the easternmost islands of the Salomonis are in the longitude of fully 220°, reckoning said longitude from the meridian of the islands of Corvo and Floris.”
The globe used the Portuguese convention, having its meridian at the Azores, which at the time the convention was adopted, was the westernmost of any known land.
Even after making adjustments for the different meridians, the discrepancy between the chart and the globe was enormous. Depending on the features compared, the globe and chart differed by between 11° and 19° of longitude.
Their instructions were to sail east, as far as the eastern extremity of the Solomon Islands… but now there was significant confusion about just where that was.
Following a complex series of calculations he decided they should rely on their newer Gerritsz map, rather than the Portuguese globe, and made a written recommendation.
Hence our advice is that we should stick to the 44th degree South Latitude until we shall have passed the 150th degree of Longitude, and then run north as far as the 40th degree South Latitude, remaining there with an easterly course until we shall have reached the 220th degree of Longitude, after which we should take a northerly course so as to avail ourselves of the trade-wind to reach the Salomonis islands and New Guinea…
…Signed, Francoys Jacobsz.
Bad weather continued to make it impossible to convene the Council, and it was not until two days later that Tasman replied to the Pilot’s message.
“Towards evening we dispatched to the officers of the Zeehaan the letter following, together with the Annotations of Pilot-major Francoys Jacobsz, the said papers being enclosed in a wooden canister-shot-case, duly waxed and closely wrapped up in tarred canvas, which case we sent adrift from the stern part of the poop; the letter duly reached its destination and ran as follows:
To the officers of the Zeehaan.
We should have greatly liked to have had your advice on the 7th instant but, time and opportunity being unpropitious, we resolved with the members of our council and our second mates to shape our course north-east as far as 44° South Latitude, and then keep a due east course as far as 150° Longitude; should you agree to this resolution then be pleased to hoist a flag at your stern as a sign of approval that we may duly ratify the resolution. We also request you to do your best to sail in during the night until further orders and, if you should think it possible to come alongside of us in the boat, be pleased to float a flag from the foretop by way of signal, in which case we shall stay for you, seeing that we are very desirous of communicating with you by word of mouth. Farewell. Actum Heemskerk sailing in about 44° South Latitude, this day November 9, 1642.
Signed, ABEL JANSZ TASMAN.
After reading the above, those of the Zeehaen hoisted the Prince-flag in sign of approbation of our resolution.”
Over the preceding days they had been pushed progressively north, and were now already at 44°S. They accordingly now set their course east.
In the preceding two weeks two decisions had been made that had completely changed the outcome of the expedition.
On the 29th Oct, in heavy fog, they had turned east. Had they continued south they would have met, most likely tragically, with the French Antarctic Lands, which would remain undiscovered until 1772.
From Mauritius, they had sailed 7,000km without sighting land. On 9th November they determined, contrary to their instructions, to run East at the Latitude of 44°S.
That decision placed them in the same latitude as the land that would subsequently bear their commanders name… Tasmania.
On Nov 11th the weather eased and they were finally able to convene the Council.
“We ran up the white flag, upon which the officers of the Zeehaen came on board of us, when we resolved in the plenary Council to run on in the parallel of about 44° South Latitude from our present longitude (averaging 123° 29′) as far as 195° Longitude, being the meridian of the east side of New Guinea as delineated in the chart.”
The Council confirmed that they should sail on in the latitude 44°S.
By 17th November they had reached the eastern extremity of their chart, and passed again into the unknown. Now they were not only further South in this ocean than any Dutchman had ever been, they were also further to the East.
“we estimated that we had already passed the South land known up to the present, or so far as Pieter Nuyts had run to eastward.”
Tasman continued to the East in mixed weather, and the journey was otherwise uneventful except for this unusual event on 22nd November.
“we found that our compasses were not so steady as they should be, and supposed that possibly there might be mines of loadstone about here, our compasses sometimes varying 8 points from one moment to another, so that there would always seem to be some cause that kept the needle in motion”.
He had sailed over a magnetic anomaly that caused his comapass to vary through a 90° arc. ‘loadstone’ (sic) is a magnetic rock, and in Tasman’s time was used to magnetize to their compass needles.
The following day he compared his position to a location we can verify.
“At noon Latitude observed 42° 50′, Longitude 162° 51′; course kept east, sailed 25 miles; we found the variation to the compass to be 1 degree North-West, so that the decrease is a very abrupt one here; by estimation the west side of New Guinea must be north of us.”
It was 47 days since he left his last known position, Mauritius, and at this point in his journal we can test his ‘dead reckoning’ estimate of Longitude.
On 22nd November he wrote that he believed the western extremity of New Guinea was now due north of his position. The western point of New Guinea lies in 130° 57′, due east of Greenwich. He estimated his longitude that day as 162° 51′, measured East from the Peak of Tenerife. This is 134° 2′ E using our contemporary convention of the Greenwich Meridian.
His longitude estimate error is 3° 5′. In terms of change in longitude from his reference point, Mauritius, this is a 4% error; or expressed the other way, Tasman’s ‘dead reckoning’ of longitude was 96% reliable.
Tasman’s journal for the next day, began innocuously…
“Good weather and a clear sky. At noon Latitude observed 42° 25′, Longitude 163° 31′; course kept east by north, sailed 30 miles; the wind south-westerly and afterwards from the south with a light top-gallant breeze.”
However, that day one of his sailors earned a bonus;
“three pieces-of-eight and a can of arrack to whoever shall first see and observe land”.
On November 24th, 1642 Tasman recorded in his journal. “In the afternoon about 4 o’clock we saw land bearing east by north of us at about 10 miles distance from us”.
The captions on this drawing read:
A view of the coast when you are six miles from it.
A view of Anthonij van Diemens Landt, when you come from the west, and are in 42½° S. Latitude.
“This land being the first land we have met with in the South Sea and not known to any European nation we have conferred on it the name of Anthoony Van Diemens landt in honour of the Honourable Governor-General, our illustrious master, who sent us to make this discovery;”
The land he named in honour of his employer, now bears his own name… Tasmania.