115 
described by Dr. Faraday in the transactions of the Royal 
Society, I was at first surprised at obtaining different results 
from those published; many metals which, according to 
Dr. Faraday, had appeared to take an equatorial position 
between the poles of the magnet, assumed the axial position 
as magnetic bodies. I soon observed that the nature or 
direction of the action upon many metals varied with the 
intensity of the magnetic force, and I found that such 
effects were in accordance with the observations of Pro- 
fessor Plucker. On this he appears to have correctly 
founded the hypothesis, that the dia-magnetic force increases 
more rapidly than the magnetic in relation to the power of 
the exciting magnet. 
Not being aware how far Professor Plucker may have 
extended his researches to the phenomena of the magnetic 
and dia-magnetic forces developed in pure metals, I con- 
ceived that the inquiry, how far such forces might be 
co-existent in the same metal, might lead to interesting 
results. In pursuing such investigations other phenomena 
presented themselves to me ; and as these in some respects 
depend upon the power of the magnet employed, I will 
describe the apparatus with which the experiments were 
conducted. My electro magnet is composed of a bar of 
soft iron IJ inches in diameter, 11 lbs. in weight, and 
about 20 inches in length, bent into a horse shoe form. 
It is covered in the usual manner with about 120 yards 
of insulated copper wire. No. 12, Birmingham wire guage, 
connected in one length. The poles of the magnet are 
about 3J inches apart, and are furnished with polar pieces, 
the distance of which can be varied from about one-tenth 
to two inches, and regulated by set screws. The polar 
pieces are tapered so as to present plane faces in the form 
of parallelograms, which are about 0.3 inches in breadth, 
and 0.2 inches in depth. I generally employ four pairs of 
