n8 Captain Kater on the best kind of steel 
obtained by the ends of the needles having been first har- 
dened at a higher temperature, and then at a lower. 
The needles were now hardened throughout at a bright 
red heat. 
Experiment 19. 
Hardened throughout at a bright red. 
Directive 
force. 
Parallelogram 
Rhombus 
Pierced rhombus - 
1120 
1205 
1080 
The needles softened by laying them on a red hot poker 
till they passed beyond the blue to a greyish white. This 
was carried to within an inch of their extremities, which re- 
mained hard. 
Experiment 20. 
Softened from the middle to a greyish 
white, ends hard. 
Directive 
force. 
Parallelogram 
Rhombus 
Pierced rhombus 
1360 
11^0 
1210 
The tempering was carried throughout the needles, the 
parallelogram was reserved for another purpose. 
Experiment 21. 
Softened throughout to a greyish white. 
Directive 
force. 
Rhombus 
Pierced rhombus 
1075 
1145 
