SOO Mr Christie’s Observations 
the ring at all southerly inclinations, as observed to be the case 
by Mr Lecount. I have been under the necessity of stating the 
results that might be expected under the different circumstances, 
in a general manner, as we are not informed at what distance 
the compass was placed from the ring ; but it is evident, that, if 
we knew this distance, we could determine accurately by the 
theory the different situations of the i( neutral” points in all po- 
sitions with the greatest facility, since it would be only necessary 
to determine the intersections of a given small circle with the 
magnetic equator. 
In estimating the effects produced on the compasses on board 
ships by the masses of iron so variously distributed about them, 
I should refer their disturbing forces to a single point, which 
might be determined experimentally, then as the position of the 
ship’s head changed, this point would revolve round the com- 
pass, and its position with regard to the magnetic equator of the 
needle, which would depend on the dip, the position of the head 
and the roll of the ship, would always point out the nature of 
the deviation, the quantity of which might in all cases be accu- 
rately computed from the proper data. Whoever compares this 
method with that which Mr Lecount was under the necessity of 
adopting, according to the theory of the changeable polarity of 
the iron, must admit, however attached they may be to that 
theory, that the one I have advanced possesses the most decid- 
ed advantages in facility of application ; and it is on these ad- 
vantages, derived from theory, that I would more particularly 
insist. 
I shall close| my observations on the experiments of Mr Le- 
count, with a few on the instructions which he recommends for 
ascertaining the dip of the needle. This consists of an iron bar, 
which can be adjusted to any angle with the horizon, and is to 
be placed in the magnetic meridian ; a compass is then to be 
carried along parallel to the bar, both above and below it, and 
the bar adjusted, so that the deviations above the bar are, 
for instance, all of the north end of the needle towards it, and 
those below of the south end, throughout the whole length; the 
inclination of the bar to the horizon will be the complement of 
the dip, of the same name as the elevated end of the bar, in the 
