int of the indicator will move through depends
upon the distance between the cores of the magnets and the
distance of the armature from these cores. These distances are
often times such that the indications of the cell are not very
definite. If the armature is moved too far from the cores there is
not sufficient pull exerted by them when magnetized, to cause the
position of the armature' to change.

Mount on the shaft carrying the armature a small gear wheel.
Arrange another smaller gear to engage this on and fasten the
indicator to the shaft of the smaller gear. Any movement now of
the armature shaft will result in a relative large movement of the
indicator shaft. Figure 11 shows the arrangement of the gears just
described.

** How to Make a Steam Calliope [418]

Secure ten gas jet valves, the part of the gas fixture shown in
Fig. 1, and prepare to place them in a piece of 1-in. pipe, 12 in.
long. This is done by drilling and tapping 10 holes, each

[Illustration: Details of the Calliope]

1 in. apart, in a straight line along the pipe. The valves screwed
into these holes appear as shown in Fig. 2. The whistles are made
from pipe of a diameter that will fit the valves. No dimensions
can be given for the exact lengths of these pipes as they must be
tried out to get the tone. Cut ten pieces of this pipe, each one
of a different length, similar to the pipes on a pipe organ. Cut a
thread on both ends, put a cap on the end intended for the top,
and fit a plug in the other end. The plug must have a small
portion of its side filed out, and a notch cut in the side of the
pipe with its horizontal edge level with the top of the plug. This
part of each whistle is made similar to making a bark whistle on a
green stick of willow. The pipes are then screwed into the valves.

The whistles may be toned by trying out and cutting off pieces of
the pipe, or by filling the top end with a little melted lead. The
1-in. pipe must have a cap screwed on one end and the other
attached to a steam pipe. The steam may be supplied by using an
old range boiler, placed horizontally in a fireplace made of brick
or sheet iron. If such a boiler is used, a small safety valve
should be attached. The keys and valve operation are shown in Fig.
3. This is so plainly illustrated that it needs no explanation.
--Contributed by Herbert Hahn, Chicago.

** Sharpening Scissors [419]

When sharpening scissors on a grindstone it is very difficult t