242 Mr. Scoresby Junior* s experiments and observations on the 
ready before the public,* the communication that I have now 
the honour of laying before the Royal Society, will be con- 
fined to the application of these laws to practical magnetism; 
and particularly to the construction of magnets, without the 
use of any magnetised substance. 
In examining the magnetical effect of percussion on differ- 
ent kinds of iron and steel, two tests were employed ; the 
weight of iron that the body would lift, and the quantity of 
deviation that it would produce on a magnetic needle when 
presented to it in a certain position, and at a certain distance. 
For the first test, common iron nails of different sizes were 
made use of : they were of the weights of 2, 4, 6j, 14, 24, 
$ 7 , 45, 88, 130, and 188 grains. For the purpose of secur- 
ing a good and uniform contact with the magnetised bar, 
the oxide on the ends of the nails was removed by means of 
a fine file, and the extremities were then polished by rubbing 
them on a turkey stone. The second test I employed, con- 
sisted of a board two feet in length, with a longitudinal line 
down the middle divided into inches, and a sensible pocket 
compass. To guard against the effects of the magnetism of 
position, the central line of the board was placed exactly in 
an east and west direction by the compass, and as the board 
was laid horizontally on a table, this line was known to be in 
the plane of the magnetic equator, and consequently in a 
situation in which small bars of iron are not affected by the 
magnetism of position. In applying this simple apparatus as 
a measure of magnetism, the bar, whose magnetism was to 
be examined or compared, was laid along the central line of 
the board, with its north pole always nearest the compass. 
* Edin. Phil. Trans. 1821. 
