deflected by the current. This, like Edison’s,
is a direction meter; but a meter in which no regard
is paid to the direction of the current can be made
by help of an iron armature of such a shape that the
force with which it is attracted to fill the space
between the poles of an electro-magnet is inversely
as its displacement. Then by resisting this motion
by a spring or pendulum the movement is proportional
to the current, and a tangent wheel actuated by this
movement causes the reciprocating cylinder on which
it runs to integrate the current strength. Mr.
Boys exhibited two such electric energy meters, that
is, machines which integrate the product of the current
strength by the difference of potential between two
points with respect to time. In these the main
current is made to pass through a pair of concentric
solenoids, and in the annular space between these
is hung a solenoid, the upper half of which is wound
in the opposite direction to the lower half.
By the use of what Mr. Boys calls “induction
traps” of iron, the magnetic force is confined
to a small portion of the suspended solenoid, and
by this means the force is independent of the position.
The solenoid is hung to one end of a beam, and its
motion is resisted by a pendulum weight, by which the
energy meters may be regulated like clocks to give
standard measure. The beam carries the tangent
wheels, and the rotation of the cylinder gives the
energy expanded in foot-pounds or other measures.
The use of an equal number of turns in opposite directions
on the movable solenoid causes the instrument to be
uninfluenced by external magnetic forces. Mr.
Boys showed on the screen an image of an electric arc,
and by its side was a spot of light, whose position
indicated the energy, and showed every flicker of
the light and fluctuation of current in the arc.
He showed on the screen that if the poles are brought
too near the energy expended is less, though the current
is stronger, and that if the poles are too far apart,
though the electromotive force is greater the energy
is less; so that the apparatus may be made to find
the distance at which the greatest energy, and so the
greatest heat and light, may be produced.
At the conclusion of the paper, Prof. W.G.
Adams and Prof. G.C. Foster could not refrain
from expressing their high admiration of the ingenious
and able manner in which Mr. Boys had developed the
* * * *
A CANAL BOAT PROPELLED BY AIR.
A novelty in canal boats lies in Charles River, near
the foot of Chestnut street, which is calculated to
attract considerable attention. It is called
a pneumatic canal boat and was built at Wiscasset,
Me., as devised by the owner, Mr. R.H. Tucker,
of Boston, who claims to hold patents for its design
in England and the United States. The specimen
shown on Charles River, which is designed to be used
on canals without injuring the banks, is a simple structure,