Balance and Sonometer. 155 



further distance apart, so as to still bring the increased mass 

 of metal in the centre of the coils. 



I have been experimenting up to the present time •with a 

 view of being able to obtain visual instead of acoustic 

 results, but so far without decided success; the extreme 

 feebleness of the induced current as it approaches its zero- 

 point fails to influence any form of galvanometer; and 

 although the principle can be exhibited by a very sensitive 

 form of galvanometer when a considerable disturbance of 

 the balance takes place, the practical value of the balance is 

 lost by its insensitiveness. 



I think I have now explained sufficiently the construction 

 of the apparatus ; it is so easily made and used that it should 

 find a place in all future phj-sical researches, and thus by 

 extending its use we may discover its exact value as a new 

 instrument of measurement. 



Art. X. — Notes on the Geology of the West Tamar District, 

 Tasmania. 



By Norman Taylor, of the late Geological Survey 

 of Victoria. 



[Read 9th October, 1879.] 



The country which I examined in the month of January 

 last contains an area of about forty square miles in the 

 parish of Phillipsnorton, county of Devon, Tasmania. It 

 is situated in the neighbourhood of the West and Middle 

 arms of the River Tamar, a district which at one time 

 gave promise of being a large iron-producing one, but 

 which has, unfortunately, after several trials and much 

 wasted capital, been temporarily abandoned, simply from 

 the unforeseen occurrence in the iron ores of an oxide of 

 chromium, the presence of which renders it impossible to 

 turn out good marketable pig .iron. 



The roughly triangular area, whose base would join the 

 heads of the West and Middle arms of the Tamar, consists 

 at its northern apex of greenstone, rising at Ilfracombe 

 village to a long ridge, capped with older pliocene tertiary 



