24jO Mr Barlow m tlm Anomalous Magnetic Action of Hot Iron 
tism of red-hot iron. The details of his experiments have since 
appeared in the Philosophical Transactions for 1822, p. 117., 
and are of such importance as to induce us to give a more full 
account of them to our readers. 
Mr Cavallo seems to have been the first person who found, that 
red-hot iron had a greater power over the magnet than cold 
iron. Captain Scoresby has more recently determined, that hot 
iron receives more magnetism of position than the same iron does 
when cold, a red hot-bar producing a deflection of 77°, whereas 
it was only 15° when cold In this state of the subject, Mr Bar- 
low was led to investigate it, and obtained the very remarkable 
results which we have formerly explained. 
The following Table contains the whole series of his experi- 
ments. The attraction which took place according to the known 
laws of magnetism is marked -f-, which ever end of the needle ap- 
proached the iron, and the opposite attraction is marked—. When 
the compass, for example, is above the centre of the bar, the 
north end of the needle should be drawn towards the iron ; but 
when the compass is below the centre, the south end should ap- 
proach the iron. These, therefore, are both marked thus -f , and 
the contrary attraction of the red heat is marked. — In the Table 
C. B. signifies Cast-Iron Bavj and M. B. Malleable Iron Bar. 
All the following experiments were made with the bars in- 
clined in the direction of the dipping-needle, and the negative 
attraction was always the greatest^ yfhcxe the natural atiYaction 
was the least, that is opposite to the middle of the bar, or in the 
plane of no attraction. Mr Barlow also tried a few experiments 
with the bar inclined at right angles to its former position ; but 
though a certain quantity of negative attraction, never exceed- 
ing 2§°, was always found, yet the results are not so strongly 
marked as in the other experiments. 
The only possible explanation which Mr Barlow offers to ac^ 
count for these anomalies is, that the iron cooling faster towards 
its extremities than towards its centre, a part of the bar will be- 
come magnetic before the other part, and thus cause a different 
species of attraction. This explanation, however, he does not 
consider as satisfactory. 
* Edinburgh Transactions^ vol. ix. part 1 . p. 254. 
