446 Transactions. — Chemistry and Physics. 



gested that no change should be made until by means of the 

 then projected submarine cable a telegraphic longitude-dif- 

 ference should have been obtained between New Zealand and 

 Sydney or Melbourne. 



The frequent corrections which have been found neces- 

 sary in Sydney's assumed longitude since then have caused 

 the change to be postponed longer than was originally con- 

 templated. But circumstances now seem favourable for 

 making it. The last alterations in the longitudes of Sydney 

 and Melbourne were announced in the "Nautical Almanac" 

 for 1898 (published in November, 1894) ; and as these were 

 based on very careful telegraphic determinations by observers 

 at Greenwich, Sydney, and Melbourne, they seem likely to be 

 practically final. Moreover, the Admiralty has in one case 

 used the latest longitude in compiling a chart. 



On the sheet to which I have referred as forming an 

 exception to the others — viz., the large-scale chart of Port 

 Nicholson (No. 1423)— the longitude is given as 174° 46' 20", 

 equivalent to 11 h. 39 m. 5-3 s. The Hydrographer to the 

 Admiralty, in a letter written by him to Sir James Hector 

 on the 1st December, 1902, explains that this determination 

 (which was the one given in the report of the Australian 

 Telegraphic Determination of Longitudes, 1886) was adopted 

 by the Admiralty in 1890, and that, although it has not been 

 considered necessary in the interests of navigation to alter 

 the existing coast charts, the value 11 h. 39 m. 53 s. will be 

 the initial point of any rearrangement w T hich may ultimately 

 be made in the Admiralty charts. He agrees that, under the 

 circumstances (the discrepancy being so small), the determina- 

 tion of the Admiralty to retain the old longitude on the ma- 

 jority of the charts need be no further bar to our "adopting 

 the quantity which is at present considered to be the most 

 correct." The value given on the large-scale chart (No. 1423) 

 is that obtained from Mr. Eu'ssell's and Mr. Adams's tele- 

 graphic work in 1883 ; and as this differs by only - 2 s. from 

 the value deduced from Mr. Eussell's and Archdeacon Stock's 

 telegraphic interchange in 1876 the way is now clear for 

 using 11 h. 39 m. 53 s. as the standard longitude for comput- 

 ing New Zealand mean time from observations taken at the 

 Observatory. 



A similar small error occurs in the longitudes given in the 

 Survey Department's land maps of the colony. These longi- 

 tudes are based on Mr. Thomson's determination of the 

 longitude of Eockyside (as amended in the manner above 

 explained) ; consequently the values are at present practi- 

 cally identical with those shown in the charts. I understand, 

 however, that the Surveyor-General purposes taking advan- 

 tage of an intended reissue of the Department's maps to 



