Time of Relative Resistance Relative Resistance
Electrification. at 0º C (32º F.) at 24º C (75º F.)
1 minute 100 5.51
2 " 127.9 6.
5 " 163.1 6.66
10 " 190.9 6.94
20 " 230.8 7.38
30 " 250.6 7.44
60 " 290.4 7.6
90 " 318.3 7.66
In cable testing one minute is generally taken as the time of
electrification.
Pressure increases the resistance by the formula Rp=R (1+ .00327 P) in
which Rp is the resistance at pressure p--R resistance at atmospheric
pressure--p pressure in atmospheres. Thus in the ocean at a depth of
4,000 meters (2.4855 miles), the resistance is more than doubled. The
longer the pressure is applied, the greater is the resistance.
The specific inductive capacity of gutta percha is 4.2.
Good gutta percha should not break when struck with a hammer, should
recover its shape slowly, and it should support much more than 300 times
its own weight.
Gyrostatic Action of Armatures.
Owing to gyrostatic action a rotating armature resists any change of
direction of its axis. On ships and in railway motors which have to turn
curves this action occurs. A 148 lb. armature running at 1,300
revolutions per minute may press with 30 lbs. on each journal as the
ship rolls through an angle of 20° in 16 seconds.
H.
(a) The symbol for the horizontal component of the earth's
magnetization.
(b) The symbol for the intensity of a magnetizing force or field. The
symbol H, as it is generally used, may mean either the number of dynes
which act upon a unit pole, or the number of lines of force per
centimeter.
(c) The symbol for the unit of self-induction.
Hair, Removal of, by Electrolysis.
A method of depilation by destruction of individual hair follicles by
electrolysis.
A fine platinum electrode is thrust into a hair follicle. It is the
negative electrode. The positive electrode is in contact with the body
of the person under treatment; it is often a sponge electrode simply
held in his hand. A current of two to four milliamperes from an E. M. F.
of 15 to 20 volts, is passed. This destroys the follicle, the hair is
removed and never grows again. A gradual increase of current is advised
for the face. As only one hair is removed at once, but a small number
are taken out at a sitting.