general level of the
rim.]

Of course this applies to a tube where economy has been exercised and
the end is short. If the tail is long enough to form a handle, the
tube may be pulled apart as before. As a rule a temporary joint
between a tube and a rod is not strong enough to enable the shoulder
to be broken at the scratch by mere pulling. The ends to be welded
must be broken off very clean and true. Subsequent operations are to
be carried out as already described.

Sec. 23. The above operations will be easily performed on tubes up to
half an inch in diameter, if they are not too long. It is the length
of tube, and consequent difficulty in giving identity of motion with
the two hands, which make the jointing of long tubes difficult. There
are also difficulties if the tubes are very thin, have a very fine
bore or a very large diameter.

All these difficulties merely amuse a good glass-blower, but to an
experimenter who wants to get on to other things before sufficient
skill is acquired (in the movement of the hands and arms) the
following method is recommended. First, use flint glass. Then,
assuming that any drawing down has to be done, do it as well as
possible, for on this the success of the method to be described
especially depends. Be sure that the tubes to be welded are cut off
clean and are as nearly as may be of the same size at the point of
junction.

To fix the description, suppose it is desired to join two tubes (see
Fig. 8), each about one inch in diameter and a yard long. Get four
clip stands and place them on a level table. Be sure that the stands
are firm and have not warped so as to rock. In each pair of clips
place a tube, so that the two tubes are at the same height from the
table, and, in fact, exactly abut, with axes in the same straight
line. Close one tube by a cork and then fix the blowing apparatus as
shown to the other.

In such an operation as this the drying apparatus may be dispensed
with, and a rubber tube simply connected to one end of the system and
brought to the mouth. Take the oxygen blow-pipe and turn the nozzle
till the flame issues towards you, and see that the flame is in order.
Then turn down the oxygen till it only suffices to clear the smoky
flame, and commence to heat the proposed joint by a current of hot
air, moving the flame round the joint. Finally, bring to bear the
most powerful flame you can get out of the blow-pipe, and carry it
round the joint so