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Art. VIII . — Observations on Magnetic Attraction. By S. II 
Christie, Esq. In a Letter to Dr Brewster. 
Sir, 
In compliance with your request, I transmit you an abstract 
of a paper of mine on Magnetic Attraction, read in May 1820, 
to the Cambridge Philosophical Society, and published in their 
Transactions, and in addition to this, I have applied the hypothesis 
there advanced to phenomena observed in different latitudes. 
In conclusion, I have adverted to the coincidence of my views of 
the subject, with the theory deduced by Ampere, from his judi- 
cious and elaborate experiments. 
In that paper, I endeavoured to account for the phenomena 
arising from the action of masses of iron on magnetised needles, 
on an hypothesis different from that generally received. It ap- 
peared to me unnecessary to suppose, that any part of a mass 
of soft iron should possess the power of repulsion, and indeed 
that almost a necessary distinction between unpolarised and po- 
larised iron was, that the one possessed the power of attraction 
alone, while the other possessed in addition that of repulsion. 
Several phenomena seemed to indicate that the iron did not act 
upon the needle in its horizontal position, but in the same man- 
ner as if the needle were inclined to the horizon, at an angle 
equal to the dip. From this view, it followed, that when the 
centre of a sphere of iron is in a plane passing through the cen- 
tre of the needle, perpendicular to the line of the dip, the upper 
and lower branches of this imaginary needle being equally acted 
upon by the iron, the horizontal needle will not be affected by 
it; that when the centre of the sphere of iron is above this 
plane, the upper or south branch of the imaginary needle being 
more attracted than the lower, the south end of the horizontal 
needle will deviate towards the sphere ; and that the contrary 
will take place when the centre of the sphere is below this plane. 
Finding that the directions, and also, as near as I could judge, 
the magnitudes of the deviations of the needle were such as 
might be expected on this supposition, I considered that this 
mode of action of the iron might be accounted for on the hypo- 
