For this simple operation most of the glass-blower's skill is required. The tube must be grasped between the first finger and thumb of both hands, and held so that the part to be operated on lies evenly between the two hands. The distance between the operator's thumbs may conveniently vary from 2.5 to 4 inches. Releasing the grip of the left hand, let the operator assure himself of his ability to easily rotate the tube about its axis--by the right thumb and finger--he will incidentally observe by the "feel" whether the tube is straight or not. A good deal of progress can be made from this point before the tube is heated at all. The operator can acquire a habit of instinctively rotating the tube by both hands, however the tube itself be moved about in space, or however it be pushed or pulled. The habit of constant and instinctive rotation is literally about one-third of the whole art of glassblowing. It is unlikely, however, that the beginner will discover that he has not got this habit, until a few failures draw his attention to it. The glass tube being held in position lightly yet firmly, and the operator being sure that he feels comfortable and at his ease, and that the blow-pipe flame (a single flame in this instance) is well under control, the preliminary heating may be commenced. With a tube of the dimensions given this is a very simple affair. Turn the air partly off, or blow gently, to get a partly luminous gas flame; hold the tube about an inch from the end of this flame, and turn it round and round till it commences to soften. In the case of soda glass it is usual to employ the gas flame only, but I find that it is better in most cases to use the hot air of a gently-blown flame, rather than have the disadvantage of the soot deposited in the alternative operation. When the glass begins to soften, or even before, it may be moved right into the blow-pipe flame, and the latter may be properly urged. It is not possible to give quite explicit and definite instructions, applicable to every case, as to when the time is ripe for passing the work into the flame, but the following notes will indicate the general rules to be observed:- (1) A thick tube must be warmed more slowly and raised to a higher temperature than a thin tube. (2) The same remark applies to a tube of large diameter, as compared with one of small diameter, whatever the thickness.