HocKEN. — Abel Tasman and Ms Journal. 123 



time whenever a clouded sky interferes witia a due observation 

 of the sun. It is untrustworthy at the best, from causes 

 which are very evident. A vessel may make much lee or lost 

 way from some ocean current, which insensibly drifts her out 

 of her course; and there are other sources of error. Hence we 

 shall not be surprised to find that, whilst Tasman's latitudes 

 are very correct, his longitudes are often considerably at fault, 

 even so much as three or four degrees. As will be observed 

 in this map of New Zealand, upon which I have projected his 

 daily course, he is wrong on the average about 3° W. — that is, 

 about 170 miles from the coast. This vast discrepancy will 

 exhibit very clearly the imperfection of nautical methods two 

 hundred and fifty years ago, and that Queen Anne's Board 

 of Longitude might well be content with any means where- 

 by the position at sea might be known within thirty or 

 forty miles of the true one. 



Before the discovery of America — the so-called New 

 World — the westernmost point of the then known world 

 was the Island of Ferro, one of the Canaries, and it was 

 therefore selected by old geographers as the prime meridian 

 from which all other meridians were calculated. Afterwards, 

 and somewhat before Tasman's time, the Peak of Teneriffe, 

 also in the Canaries, was selected, probably because of its 

 conspicuous height. It is from this meridian, then, that 

 Tasman gives his longitudes. In the present day all nations 

 agree as a matter of great convenience to calculate from 

 Greenwich, with the exception of the French, who, whilst 

 notating their parallels from Paris, nevertheless add the Green- 

 wich equivalent. Whilst Tasman gives, in both his chart and 

 Journal, his positions as deduced from the Peak of Teneriffe, 

 they must really be computed from the Island of Mauritius, 

 which, as we shall presently see, was his final point of de- 

 parture after leaving Batavia. So that, to reduce his longi- 

 tudes to those of Greenwich, we must subtract, say, 21° 2' 

 from them — made up of, say, 16^° for Teneriffe and 44-° error 

 for Mauritius. We then have remaining what may be called 

 "personal errors," caused by inability to calculate his posi- 

 tion exactly, and which, as has been seen, often amount 

 to three or four degrees. Another explanation should here 

 be made. The distances sailed are in Dutch miles, fifteen 

 of which are equal to one degree. A Dutch mile is equal 

 to about four English, so that if Tasman gives as his day's 

 work twenty miles we should reckon that he had sailed 

 eighty. In making this translation I have preferred to 

 give Tasman's own unaltered details ; those who desire to 

 make the corrections can do so from the data I have given. 



In a paper read before this Institute last year I gave some 

 account of Tasman's Journal, and showed that it had never 



