86 MAGNETIC SURVEY OF TASMANIA. 



utilitarian aspect, as it may contribute information of 

 ^reat importance to the sciences of navig'ation and 

 surveying. 



I will now proceed to lay before tliis Society a brief 

 account of the work proposed to be done by Professor 

 M'Aulay and myself in connection with the magnetic 

 survey of Tasmania, which it is our intention to begin 

 during the coming summer. 



The instruments to be employed are the bifilar mag- 

 netometer and declinometer of the latest Kcav pattern ; 

 they have been lent to vis by the University of Sydney, 

 through the kind offices of Professor Pollock of that 

 University. 



Having regard to the short time — 8 or 10 weeks — 

 during which the instruments will be at our disposal, we 

 consider that the most valuable results will be obtained 

 by limiting our observations, for this summer at least, to 

 about 10 well-selected stations. By this means we hope 

 to be able to get a fairly complete grip of the general 

 magnetic distribution in Tasmania, and expect that tbe 

 information disclosed by this summer's work will be of 

 the greatest value when we come to select stations of 

 observation at any future time. The stations we propose 

 to select are : — Hobart, Port Esperance, Port Davey, 

 Strahan, Mt. Lyell, Wynyard, Longford, Scottsdale, 

 St. Helens, Spring Bay. If time permit, Oatlands will 

 also be made a station of observation. It will be seen 

 that the places selected are fairly spaced through the 

 Island of Tasmania ; if the magnetic elements are 

 determined at these points, it will be easy to compute 

 them approximately for any other station. 



Our selection of the stations enumerated has been 

 largely guided by geological considerations, owing to 

 the prevalence in Tasmania of magnetic rocks. At a 

 meeting of this Society held as far back as the 2nd 

 April, 1845, attention was drawn by Mr. R. C. Gunn to 

 the magnetic properties of the greenstone taken from 

 the summit of Brady's Look-Out, and most surveyoi's of 

 experience in Tasmania can testify to abnormal devia- 

 tions of their compasses arising from masses of green- 

 stone and basalt close at hand. An interesting illustra- 

 tion of this is to be found in the University grounds, 

 where the declination varies from 7° E. to 11° E., 



