88 MAGNETIC SURVEY OE TASMANIA. 



of constructing" tlic iiia|) of Ta!?mania. A full descrip- 

 tion of the exact locality of each site of observation will 

 he lodged with tlie Surveyor-General, together with a 

 detailed account of the method employed to lay out the 

 meridian. 



It is scarcely necessary for me to detain the members 

 of this Society by pointing out the importance, to all 

 concerned with navigation, of an accurate knowledge of 

 the magnetic declination, and of its rate of variation. 

 So many of our selected stations are on the shore-line of 

 Tasmania, that we hope to be able to make some con- 

 siderable additions to the information already acquired 

 on these points. 



With the exception of the large properties of the Van 

 Diemen's Land Company, whose boundaries were laid 

 down by astronomical methods, it may be said that 

 surveying in Tasmania has been, in the past, practically 

 based on magnetic methods. The element of uncertainty 

 introduced into surveys by the variation of the declination 

 may not obtrude itself in any Held work for some time, but 

 directly any attempt is made to collate the county maps 

 with the trigonometical survey, there is reason to fear 

 that grave discrepancies will show themselves. Survey- 

 ing according to astronomical methods is in many parts 

 of Tasmania very tedious and difficult, owing to the 

 climate, and a more complete knowledge of the declination 

 than is now possessed would be useful and convenient 

 to surveyors, especially in the case of isolated surveys, 

 and groups of surveys being made in new districts. 



It is to be hoped that before long the trigonometrical 

 survey of Tasmania will be proceeded with, so that a 

 new map of the Island may be compiled ; and it is 

 probable that much information of value towards this 

 end may be collected during the magnetic survey. 



There are long gaps in the magnetic history of Tas- 

 mania, but when an accurate knowledge of the variation 

 of the magnetic elements has been again attained, it may 

 be possible, by analysing the magnetic records of Mel- 

 bourne and Sydney, to reconstruct the past magnetic 

 history of Tasmania, and form an approximately correct 

 idea of the magnetic changes which have taken place 

 since Lieutenant Kay first set up his instruments, in 

 Hobart some sixty years ago. 



