lame which is very annoying
and makes good work very difficult. When compressed air is available it
can be used, but if possible it should be arranged so that the supply
can be controlled by the foot, as both hands are usually needed to hold
the work. For the same reason the supply of air is usually regulated by
varying the rate of operation of the bellows, rather than by adjusting
the valve of the blast-lamp. On the other hand, it will be found best to
always adjust the flow of the gas by means of the cock on the lamp,
rather than that at the supply pipe. The operator must have complete
control over the flame, and be able to change its size and character at
short notice without giving the work a chance to cool, and often without
ceasing to support it with both hands.

Glass-blowing should be done in a good light, but preferably not in
direct sunlight. The operator should be seated in a chair or on a stool
of such a height that when working he may comfortably rest one or both
elbows on the table. The comfort of the operator has a decided influence
on the character of his work; especially in the case of a beginner, who
often defeats his purpose by assuming uncomfortable and strained
positions. Steadiness and exact control of both hands are essential in
most operations; any uncomfortable or strained position tires the
muscles and weakens the control of the operator over them.

In the arrangement of the exercises here presented, several factors have
been considered. It is important that the first exercises be simple,
although not necessarily the simplest, and they should teach the
fundamental operations which will be used and amplified later. They
should in themselves be things which are of importance and commonly used
in glass-work, and they should be so arranged that the fundamental
points, such as the rotation of glass, the proper temperature, blowing
and shrinking the glass may be learned with a minimum expenditure of
time, glass and gas. It is therefore recommended that the beginner take
them up in the order given, at least as far as No. 7, and that each be
mastered before attempting the next. The beginner should not leave the
first exercise, for example, until he can join together two pieces of
tubing so that they form one piece of substantially uniform inner and
outer diameter, and without thick or thin spots. From two to four
practice periods of two hours each should suffice for this. This chapter
and the followin