OPTICAL PROJECTION
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worked in the middle of a room, it is very important to re¬
serve enough space for the gas-bags or cylinders comfortably,
and to have this space protected by making a kind of fence
with some of the seats, within which no one is allowed to
come. If it is a juvenile audience, it is important to get some
elder lad appointed to act as sentinel over this.
The connections are made as in the diagram, which shows
a star-tap (as the most puzzling). The hydrogen is connected
from the bag or cylinder to the
nozzle across which the bye-pass
is fitted, if only one ; otherwise
to the one known to have the
longest channel. (If the jets
both persist in snapping out,
with a tap that has two bye-
passes, it is probable the gases
are taken to the wrong nozzles
supplying the dissolver, and that,
from the unequal length of chan¬
nel, the hydrogen cuts off before
the oxygen). In the diagram,
the hydrogen goes to the left,
the oxygen to the right-hand
nozzle. The tubes carrying from
the dissolver to the jets may be
connected to either top or bottom
lantern, as regards one of the
gases, provided the other gas be connected to correspond. In
the diagram the top hydrogen nozzle goes to the top jet, and
therefore the bottom oxygen nozzle must connect to the same
jet. With the other form of dissolver (fig. 61) both nozzles
on the same side go to the same jet, and the cylinders or bags
connect with the centre pair, and no mistake can be made by
a person of ordinary sense.
The lantern lenses will now be wiped over if necessary,
Pig. 63.—Connections