but
all connected so as to act in perfect unison. The thinnest sheet brass or
iron obtainable should be used, so that the tension of the spring used to
close the shutter need not be great. Our illustration shows a two-part
shutter, each half an inch wider than the hole in the front, and jointly a
similar amount deeper. The upper half overlaps the lower, outside, by a
quarter of an inch.

The spindles are two straight pieces of brass wire, revolving in sockets
which are most easily made of notched pieces of wood (as shown in Fig.
189), with removable caps of strip tin. The lower spindle should be an inch
longer than the width of the front, to allow for a cranked end, to which
the closing spring will be attached.

Having cut out the halves of the shutter, solder the spindle wires to one
edge of each on what will be the back side. The wires must be so arranged
as to allow a quarter of an inch to project beyond the left edge of the
front, as the opening mechanism is situated on this side as the most
convenient for the operator.

Take a couple of metal discs, an inch or so in diameter, and bore a hole in
each near the circumference to fit the ends of the pivots fairly tight.
Three-eighths of an inch from this--centre to centre--bore and tap a hole
for a small screw. The tapping should be done with a taper tap and carried
just so far that the screw turns stiffly without danger of being broken off
by the screw-driver.

Next find the correct positions of the parts of the shutter and the spindle
sockets on the front of the holder, and mark them off carefully. Screw the
wooden parts of the sockets to the front. Four little "distance pieces"
should now be cut out of small tubing, or made by twisting tin round the
spindle, to place on the spindles between shutter and sockets, so that the
shutters cannot shift sideways.

The right-hand end of the lower spindle must be bent over (after slipping
on the distance piece) to form a 1/2-inch crank making an angle of 45
degrees with the line of the front, in an upward direction, as it will be
depressed by the opening of the shutter. Flatten out the end with a hammer,
and drill a small hole near the tip.

The shutters can now be placed in position, and the caps of the sockets be
screwed on. The next thing to make is the connecting rod to join the cranks
at the left side of the front. For this purpose we may use a piece of
fairly stiff strip metal--brass by preference--5 or 6 inches lo