Porous Cup.
A cup of pipe clay, unglazed earthenware or other equivalent material
used in voltaic cells to keep two liquids separate and yet to permit
electrolysis and electrolytic conduction.
They are necessarily only an expedient, as their porous nature permits
considerable diffusion, and were they not porous electrolytic action
would be impossible.
Synonym--Porous Cell.
Porret's Phenomenon.
In electro-physiology, an increase in the diameter of a nerve produced
by the positive pole of a voltaic circuit, when placed in contact with
the tissue and near to the nerve in question, the other pole being
connected to a more or less remote part of the body.
Portelectric Railroad.
A railroad worked by solenoidal attraction, the car forming the core of
the solenoids. It includes a series of solenoids or hollow coils of
copper wire distributed all along the road and inclosing within
themselves the track. On this a cylindrical car with pointed ends moves
on wheels. Current is supplied to the solenoid in advance of the car,
and attracts it. As it advances it breaks the contacts of the attracting
solenoid and turns the current into the one next in advance. This
operation is repeated as the car advances.
The solenoids are placed close together, each including in the trial
track 630 turns of No. 14 copper wire. The car was of wrought iron, 12
feet long, 10 inches in diameter and weighing 500 lbs. It was proposed
to employ the system for transportation of mail matter and similar uses.
Position Finder.
An instrument for determining the position of objects which are to be
fired at from forts. It is designed for use from forts situated on the
water.
Fiske's position finder may be thus generally described. On a chart the
channel is divided into squares, and the position finder determines the
square in which a vessel lies. For each square the direction and
elevation of the guns is calculated beforehand. The enemy can therefore
be continuously located and fired at, although from smoke or other cause
the object may be quite invisible to the gunner.
It comprises two telescopes situated at distant extremities of as long a
base line as is obtainable. These telescopes are kept directed upon the
object by two observers simultaneously. The observers are in constant
telephonic communication. As each telescope moves, it carries a contact
over an arc of conducting material. Below each telescope is an arm also
moving over an arc of conducting material. These arcs enter into a
Wheatstone bridge and are so connected that when the arm and the distant
telescope are at the same angle or parallel a balance is obtained. Thus
each observer has the power of establishing a balance. A chart is
provided for each of them, and over it the arm connected with the
distant telescope and an arm or indicator attached to the telescope at
that station move so that as long as both telescopes point at the object
and each observer maintains the electric balance, the intersection of
the arms shows the position on the chart.
The Position Finder is a simplification and amplification of the Range
Finder, q. v. In practice the observers may be placed far from the
forts, and may telephone their observations thereto. It has been found
accurate within one-third of one per cent.