ELECTRODYNAMIC QUALITIES OF METALS. 
59 
paper the ballistic galvanometer), the “ throw ” of which, as observed on a scale placed 
120 centims., or 2400 of its own divisions, from the mirror, measured the strength of 
the induced current. This galvanometer was placed within a case of thin sheet copper } 
and the whole enclosed within a glass bell jar to guard it from the effects of currents 
of air. 
205. The procedure in experimenting was similar to that described in Part VI., § 186 
(Trans, for 1876, p. 697). One observer took the readings of the ballistic galvanometer, 
and made and broke the circuit of the magnetizing current; while a second, on word 
of command from the first, applied or removed the weight, and noted the elongations 
or contractions of the wire, as shown by the pointer and scale described above. The 
results were entered in the register on the system followed in my previous experiments, 
according to which +M denoted that the current was made in such a direction as 
to cause the image on the scale of the ballistic galvanometer to move towards the 
right or towards increasing numbers; —M, that the current was made in the contrary 
direction ; B, that the current was stopped; Z, the zero of the ballistic galvanometer 
scale; “ On,” the application of the weight; and “Off,” its removal. The polarity of 
the magnetization produced in the wire by +M was the same as that shown by the 
wire when under the influence alone of the vertical component of the earth’s magnetic 
force ; and consequently a deflection of the image on the scale of the ballistic galvano¬ 
meter towards the right, produced by a change in the magnetic condition of the wire 
after it had been thus magnetized, indicated an increase of its magnetization, and 
a deflection to the left a diminution of its magnetization. This magnetization produced 
by -f-M, I shall call positive magnetization, and that produced by —M negative 
magnetization. Hence a deflection of the ballistic image towards the right indicates 
an increase of positive magnetization, and a deflection towards the left, a diminution of 
positive, or an increase of negative, magnetization. 
206. The conclusions of the preliminary notice of June 17, 1876, and the state¬ 
ments of § 198, are proved by the following table of results obtained by a very careful 
repetition of the experiments referred to in that notice. The first column of results 
in the table gives the operations in the order in which they were performed; the 
second, the deflections of the image on the scale of the ballistic galvanometer obtained 
after each operation; and the third column gives the battery strengths. During the 
whole of the experiments cold water was kept flowing from the cistern B through the 
channel between the coils to the vessel H, to prevent any heating of the coils and 
wire by the passage of the magnetizing current. The amount of the elongation and 
contraction of the wire by the application and removal of the weight of 14 lbs. was 
constant throughout the experiments. The experiment was begun with zero current 
in each case, and the weight of 14 lbs. applied and removed until equal and opposite 
effects were obtained by on and off; and the same process was followed after each 
augmentation of the magnetizing current. The table contains for each step only the 
results obtained after this state had been reached. 
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