magnetical properties in steel and iron by percussion. 243 
The compass was placed with its centre at the commence- 
ment of the scale, so that its needle was exactly at right 
angles to the direction of the bar ; and before the deviation 
took place, both its poles were equidistant from the bar. 
The distance was estimated by the scale on the board, and 
always represented the space between the north end, or 
nearest end of the bar, and the centre of the compass. 
Three hammers were also employed : No. I. of 22 ounces ; 
No. II. of 12 ounces ; and No. III. of qj ounces weight. 
It may be remarked, that no exact value can be given to 
the number of blows, because, having struck them by the 
hand, they must have been liable to considerable variation in 
intensity ; and also, that the lifting power cannot be consi- 
dered as an exact measure of the magnetism developed by 
the process. The deviation, however, produced on the com- 
pass by the bodies presented to it at equal distances and in 
the same direction, was decisive as a comparative measure of 
their magnetisms ; for, though the actual magnetic force is 
not given by this means, yet it is clear that a greater or less 
deviation, must be the effect of a greater or less magnetic 
force; while in bars of a similar kind and dimensions, an 
equal deviation must be the effect of equal magnetic forces. 
