+ 
in changing the dimensions of Iron and Steel bars. 85 
iron, Nos. 1 to 6 inclusive. Before commencing the experi- 
ments on the rods of steel, the distance of the scale from the 
mirror was changed, and in this new position I found that ore 
division of the scale corresponded to 0°000146 of an inch. 
Description of the helix and measures of the resistances of is wires. 
copper wire. The two inner layers formed 1069 turns of one 
length of 303 feet of wire 087 inch in diameter. The two 
outer layers were formed of another length of 330 feet of -112 
inch wire wrapped in 850 turns. These two helices could be 
used separately, or joined into one helix of 633 feet having 
1919 turns. 
The resistance of the inner helix was ‘44 ohm; the outer had 
a resistance of ‘31 ohm; together giving a resistance of ‘75 
ohm. The latter resistance, added to that of the wires leading 
from the battery through a Gaugain galvanometer to the helix 
and back to the battery, brought up the resistance to nearly 
one ohm. 
_A battery of 25 cells of Bunsen was used in the determina’ 
tions of the coefficients of elongation and retraction ; and the 
above interpolar resistance showed that the maximum effect of 
magnetization would be given by connecting the 25 cells, 5 
in couple and 5 in series. : 
_ Whenever in this research we speak of the effect of 25 cells, 
It is to be understood that they are connected as just described. 
The tron and steel rods used in the experiments were prepared 
for me with the well-known skill and fidelity of Mr. William 
Wallace of Ansonia, Ct. He carefully selected the material, 
and annealed the iron rods by packing them with iron scales 
from a rolling mill, in a wrought-iron covered box, and anes 
ing the box toa red heat for three days; the box was the 
allowed to cool very slowly. The steel rods were tempered as 
uniformly as possible throughout their lengths 
Arrangement of the Apparatus, and general description of the 
Phenomena which take place on the magnetization and demag- 
netization of the rods of tron. 
The beam supporting the apparatus was so placed that the 
axis of the ie. was Aa the ee meridian. Each rod, 
before it was introduced into the helix, was tested, as to its 
magnetic condition, by placing its length at right angles to the 
Magnetic meridian and pointing it toward the center of a mag- 
hetic needle. When the rod, thus directed, gave indications of 
polarity, its S end was placed downward with the axis of, the 
Tod in the line of the dip, and its upper end was struck with a 
light mallet. The rod was tested, until after one or more opera- 
