126 Captain Kater on the best kind of steel 
Experiment 3 6. 
Directive 
force. 
Long parallelogram 
22 75 
Short parallelogram 
1193 
They were now hardened at a red heat, and tempered be- 
yond the blue from the middle to within an inch of the 
extremities. 
Experiment 37. 
Directive 
force. 
Long parallelogram 
Short parallelogram 
2277 
1865 
If the mean of these two experiments be taken, it will be 
found, as was observed by Coulomb, that the directive force 
of a needle of a greater length than 5 inches is probably as 
its length. 
My next object was to repeat the very interesting experi- 
ments recently published by Mr. Barlow, proving the attrac- 
tion of iron on a ship’s compass to be dependant wholly on 
extent of surface. For this purpose I had three cylinders 
made of soft iron, about two inches and a half in diameter, 
and nearly the same in height. One of the cylinders was of 
sheet iron, less than the 20th of an inch in thickness ; the 
second of that kind called chest plate, 0,185: inch thick; and 
the third was of solid wrought iron. The first weighed 2760, 
the second 9376, and the solid cylinder 22929 grains. Pre- 
