a vertical position, and the bulb at the top of it. Gravity
will then shorten the bulb nicely.

The finished bulb should be a nearly perfect sphere, with the axis of
the tube passing through its center, and the portion of the tube
adjoining the bulb must not be distorted, twisted, or blown out. In
order to prevent the distortion of the tube, care must be taken that it
is never heated quite to its softening point during the process.

EXERCISE NO. 7

BLOWING A BULB IN A TUBE

The tube is selected and one end closed as in the previous exercise, but
it should be cut a little longer, say about twelve inches. Beginning at
a point about four inches from the closed end, glass is collected and
blown into a thick-walled bulb, exactly as in the previous exercise.
Greater care must be taken, however, that the cylinder collected and
this thick bulb are of uniform thickness and set squarely in the axis of
the tube. Instead of removing the tail, the bulb must be blown in this
case with both pieces of tubing attached, and care must be taken that
they "line up" properly, _i.e._, are in the same straight line, and that
this line passes as near as may be through the center of the bulb. The
tube is held in approximately horizontal position during the blowing of
the bulb, as in the previous case, and especial care taken with the
rotation. Both pieces of tube must of course be rotated at the same
rate, and their softened ends must be kept at exactly the proper
distance from each other, so that the bulb may be spherical and not
elongated. If the blowing of the bulb be quickly and accurately done, it
may usually be completed before the glass is quite set, and the
alignment of the two tubes may then be rectified while looking straight
through the bore of the tube.

=Discussion.=--The two points of greatest importance are the collection
of the glass, and the uniform rotation of the tube. A larger tube may be
sealed in the middle of a small one when a large amount of glass is
necessary. The piece of tubing used for the exercise must be long enough
so that the fingers may be kept on a cool part of the glass without
getting uncomfortably near the ends of the tube. It should not be any
longer than necessary, however, as the extra weight and length make the
manipulation of the hot glass more difficult.

When a string of bulbs are required on the same tube, a piece of glass
18 inches long may be used at the start, and the first bulb made near