+-----------------+---------------------------+------------------+ | | | | | Diameter of the | Diameter of the |Height of the wick| | wick, | orifice of the |above the surface | | _in inches_. | beak, | of the oil, | | | _in parts of an inch_. | _in inches_. | | | | | +-----------------+---------------------------+------------------+ | ¼ | 96th | ½ | | ½ | 48th | ½ | | 1 | 24th | ¾ | | 1½ | 16th | 1 | | 2 | 12th | 1¼ | +-----------------+---------------------------+------------------+ It must be mentioned, that this table has been formed from experiments made with a glass-blower’s lamp of the ordinary construction; so that, with the new lamp with the hood, described in this work, it will not be necessary to employ wicks of so great a bulk, nor yet to elevate them so much above the level of the oil, in order to produce the same effect. Hence there will be a very considerable saving in oil. The wicks of a quarter of an inch in diameter are only adapted for mineralogieal examinations, for soldering very fine metallic substances, and for working very small tubes. When the objects are of considerable bulk, it is in general necessary to have a flame sufficiently large to cover the whole instrument, or at least all the portion of the instrument which is operated upon at once. For working tubes, of which the sides are not more than the twelfth of an inch in thickness, you should have a wick at least as wide as the tube that is worked upon. The diameter of the lamp-wick usually employed is _one inch_; a wick of this size is sufficient for all the glass instruments which are in common use. THE ART OF GLASS-BLOWING. II.--_Preliminary Notions of the Art._ THE FLAME. It is only by long habitude, and a species of routine, that workmen come to know, not only the kind of flame which is most proper for each object they wish to make, but the exact point of the jet where they ought to expose their glass. By analysing the flame, upon the knowledge of which depends the success of the work, we can immediately obtain results, which, without that, could only be the fruit of long experience. Flame is a gaseous matter, of which a portion is heated to the point of becoming luminous; its form depends upon the mode of its disengagement, and upon the force and direction of the current of air which either supports its combustion or acts upon it mechanically. (Pl. 1, fig. 1.)