MAGNETIC SURVEY OF TASMANIA. 81 
A PRELIMINARY MAGNETIC SURVEY OF 
TASMANIA, 1901. 
By Proressors A. McAutay, M.A., and E. G. Hoaa, M.A. 
THE record of magnetic work in Tasmania begins with the 
determination by Sir John Franklin in 1839 of the detlina- 
tion of Lachlan, a small township about 25 miles from 
Hobart. This he found to be 10° 10’. Nothing is known 
’ as to the instrument used by him in his determination. 
During the period from 1342 to 1850 magnetic observa- 
tions were made by the survey party sent out to. Hobart by 
the Royal Society of London, under the superintendence of 
Lieutenant Kay, R.N. The resulis obtained may be summed 
up as follows:——The mean declination of Hobart varied from 
9° 53' 19’ BE. in 1843 to 10° 0' 37"! E. in 1848, giving an 
annual! increase of about 1/ 27-8". | The dip decreased from 
70° 42' 18" im 1842 to 70° 32! 0!' in 1845; it then began 
to increase, and in 1848 had attained the value of 70° 
35/ 42/f. During the period under consideration the hori- 
zontal force passed through a mmimum value in 1848. 
In 1863 Dr. Neumayer visited Hobart, and found that 
the mean declination of Hobart was then 10° 25’ 9°’, a 
quantity somewhat greater than it should have been if 
the rate of increase found by Kay had held good until 
1853. It is known that Neumayer did not use the same 
station as Kay, and as both stations employed by these 
observers are in close proximity to the highly-magnetic 
greenstone, we may have here a solution of the slight dis 
crepancy which appears to exist. Assuming that‘ Neu- 
mayer’s results are correct. and it is probable that this 
experienced observer had at his disposal more perfect instru- 
ments: than those used by Kay, the mean annual rate of 
‘increase of the declination between 1643 and 1863 would be 
1/ 38", as against 1/27-6'' con:puted from Kay’s observa 
tions. 
The next determination was made in 1881 by His Excei- 
leucy Sir J. H. Lefroy. He found the declination to be 
8° 49! 2". Tf the rate of increase deduced from Kay and 
Neumayer’s observations had held good up to 1881, the 
declination should have been 10° 53!’ 48’! Thovga Sir 
Henry Lefroy worked with a prismatic compass, the dis” 
crepancy—amounting to more than 2°—between the 
observed and calculated values can hardly be put down tc 
G 
