TRANSACTIONS 
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NEW ZEALAND I N s TAPE T E, cm 
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1873. 
; IL—MISCELLANEOUS. 
Авт. L—On the Variation of the Declination of the Magnetic Needle in the 
` Southern Portion of the Middle Island, and Remarks on the Desirability of 
Establishing Magnetic Observatories in New Zealand. Ву A. H. Ross. 
[Read before the Otago Institute, 24th April, 1873.] 
WHEN a magnetized steel bar is placed on a vertical axis through its centre 
of gravity, on which it is free to revolve, the axis being between its poles, it 
will oscillate on each side of a certain determinate position, in which, at 
length, it will come to rest. When in this position a vertical plane passing 
through the axis and the poles is called the magnetic meridian. This plane 
generally forms an angle with the plane of the true meridian of the place in 
which the magnet is situate. This angle is called the declination of the 
magnet. It is, perhaps, better known to British sailors and others as the 
variation of the compass. It is to this property of the magnetic needle that 
I propose to direct attention in this short paper, more particularly, however, 
to some remarkable variations in declination which occur in different localities 
in this Province which have come under my notice. 
The declination of the magnetic needle is subject to variations of several 
_ kinds—secular variation, annual and diurnal variation, accidental variations 
or perturbations, and local variations. 
Observations carefully taken in London and Paris, and extending over a 
period of nearly three hundred years, show that from about the year 1580 the 
declination was E. of N. in those places, but decreasing, which it continued to 
` do, until 1657, when the magnetie and terrestrial meridians were coincident, 
and remained so until 1663. A westerly declination then commenced, and 
continued increasing, though not regularly, until 1818, when, at London, a 
