ot in
use the wire is unhooked from the tree and

[Illustration: Details of the Trolley and How It Is Used]

hauled into the barn and coiled loosely in the hay loft. The wire
was made taut for use by a rope which was fastened to the beams in
the barn. The trolley was made, as shown in Figs. 1 and 2, of
strips of wood bolted with stove bolts on two grooved pulleys. The
middle wide board was made of hardwood. The wheels were taken from
light pulley blocks and stove bolts were purchased from a local
hardware store to accurately fit the hubs. As it was necessary to
keep the bearings greased, we used vaseline. This coaster made
great sport for the youngsters and at no time were they in danger
of a serious fall as the line was hung low and the slant of the
wire was moderate.
--Contributed by H. J. Holden, Palm Springs, Calif.

** How to Make an Electric Furnace Regulator [388]

We have a furnace in our house and a part of my work each evening
last winter was to go down in the basement at 9 o'clock, fill the
furnace with coal for the night and stay there until it was
burning in good shape, then to close the draft door. As this
performance requires from twenty to thirty

[Illustration: Details of Furnace Regulator Construction]

minutes I concluded to make a self-acting device which would close
the draft and leave the furnace safe, without any further
attention on my part, after putting in the coal and opening it up
to burn. As some other boys may like to build the same regulator I
will tell just how to make one and how it operates.

Referring to Fig. 1, you will see a straight cord is attached to
the draft door of the furnace, D, and is run over the pulley P and
finally is attached to a small piece of iron H. This piece of
iron is hinged to 1. To the other side of H another cord G is
fastened, which passes over the pulley N and terminates in any
convenient place in the rooms above. This piece of iron H is held
in place by the release A. Now C is a coil of wire from a door
bell. R is an armature which works A on pivot J. M is a U-tube,
filled with mercury, one end being connected to a half liter glass
flask F by the tube T, and the other end terminates in an overflow
tube O. B is a battery of three bichromate cells which are
connected up with the C and the platinum points 1--2, which are
fused into the U-tube.

On fixing the furnace the iron piece H takes position X, this
being the normal position when draft doo