perfectly light-tight, the best material to use being matched
boards. These boards are tongued and grooved and when put together
effectually prevent the entrance of light.

The next important thing to be considered is to make it
weather-tight, and as far as the sides are concerned the matched
boards will do this also, but it is necessary to cover the roof
with felt or water-proof paper.

The best thickness for the boards is 1 in., but for cheapness 3/4
in. will do as well, yet the saving is so little that the 1-in.
boards are preferable.

The dark room shown in the accompanying sketch measures 3 ft. 6
in. by 2 ft. 6 in., the height to the eaves being 6 ft. Form the
two sides shown in Fig 1, fixing the crosspieces which hold the
boards together in such positions that the bottom one will act as
a bearer for the floor, and the second one for the developing
bench. Both sides can be put together in this way, and both
exactly alike. Keep the ends of the crosspieces back from the
edges of the boards far enough to allow the end boards to fit in
against them.

One of the narrow sides can be formed in the same way, fixing the
crosspieces on to correspond, and then these three pieces can be
fastened together by screwing the two wide sides on the narrow
one.

Lay the floor next, screwing or nailing the boards to the
crosspieces, and making the last board come even with the ends of