Deviation, Semicircular.
Deviation of the compass in iron or steel ships due to vertical
induction. (See Induction, Vertical.) The effect of this induction
disappears when the ship is in the electric meridian. Its name is
derived from the fact that a swing of the ship through half the circle
brings the needle from zero deviation to a maximum and back to zero.
Dextrotorsal. adj.
Wound in the direction or sense of a right-handed screw; the reverse of
sinistrotorsal, q. v.
Fig. 128. DEXTROTORSAL HELIX.
Diacritical. adj.
(a) The number of ampere turns, q. v., required to bring an iron core to
one half its magnetic saturation, q. v., is termed the diacritical
number.
(b) The diacritical point of magnetic saturation is proposed by Sylvanus
P. Thompson as a term for the coefficient of magnetic saturation which
gives a magnet core one-half its maximum magnetization.
Diagnosis, Electro.
A medical diagnosis of a patient's condition based on the action of
different parts of the body under electric excitement.
Diamagnetic. adj.
Possessing a negative coefficient of magnetic susceptibility; having
permeability inferior to that of air. Such substances placed between the
poles of a magnet are repelled; if in the form of bars, they tend to
turn so as to have their long axis at right angles to the line joining
the poles. The reason is that the lines of force always seek the easiest
path, and these bodies having higher reluctance than air, impede the
lines of force, and hence are as far as possible pushed out of the way.
The above is the simplest explanation of a not well understood set of
phenomena. According to Tyndall, "the diamagnetic force is a polar
force, the polarity of diamagnetic bodies being opposed to that of
paramagnetic ones under the same conditions of excitement." Bismuth is
the most strongly diamagnetic body known; phosphorus, antimony, zinc,
and many others are diamagnetic. (See Paramagnetic.)