and form for a compass needle . 113 
The springs of clocks are made by passing the steel between 
rollers; and it thus undergoes great compression. May not 
this state be favourable to magnetism ; and the repeated ex- 
pansion of the steel by heat, destroying this state, have oc- 
casioned the deterioration I have remarked ? 
The needle which was made of saw blade having suffered 
less than the others in the preceding experiments, I procured 
three other needles of this material ; they were cut out of the 
same plate ; the weightof each was 120 grains, and their length 
four inches and a half. One was a parallelogram, 0,46 inch 
wide ; another a rhombus, as before, 0,87 inch wide ; and the 
third a pierced rhombus, having the middle 1,5 inch, and its 
sides 0,25 wide. 
These needles were made without its being found necessary 
to soften the steel plate ; they consequently were all as nearly 
as possible of the same degree of temper. In this state they 
were magnetized. 
Experiment 11. 
Steel the same as worked. 
Directive 
force. 
Parallelogram 
Rhombus 
Pierced rhombus 
1143 
1020 
1085 
Wishing to try whether the needles were magnetized to 
saturation, I carefully re-magnetized them. 
MDCCCXXI. 
Q 
