120 
Captain Kater cm the best hind of steel 
1210 ; but if we refer to Experiment 6, it may be seen that 
the greatest directive energy of the clock spring rhombus was 
844, which gives it an advantage of about one third in directive 
energy over a needle of equal weight made of saw blade. 
From Experiment 20, it should seem that a needle is sus- 
ceptible of the greatest directive power, other circumstances 
being similar, when it is hardened throughout at a red heat, 
and then softened from the middle to within an inch of the 
extremities, till the blue colour which arises has again dis- 
appeared. 
I next proceeded to try, in a more regular manner, the effect 
of different methods of magnetizing, and at the same time to 
ascertain whether the directive force was influenced by extent 
of surface, independent of mass. Two needles were made 
of the same kind of steel, in the form of right-angled paral- 
lelograms, five inches long, the one 0,7 inch wide, and the 
other half this width. The widest was reduced in thickness 
until it was of the same weight as the other, viz. 142 grains. 
They were in the same state of softness as was necessary to 
work them. The magnets were placed together perpen- 
dicularly oil the centre of the needle, their opposite poles 
being joined ; their lower extremities were then separated 
and kept asunder by placing a piece of wood a quarter of an 
inch thick between them, their upper extremities remaining 
in contact. The magnets were then slid along the needle 
backwards and forwards from end to end : this was repeated 
on both sides, till it was conceived the needle must be satu- 
rated. 
