if it were directed toward a cylinder.  In getting up his new chimney, Mr. Bayle has utilized these principles as follows:  Round-burner lamps have, as well known, two currents of air—­an internal current which traverses the small tube that carries the wick, and an external one which passes under the chimney-holder externally to the wick.  In giving the upper part of the chimney, properly so called, the form of a truncated cone whose smaller base is turned toward the internal current of air, that is to say, in directing this current toward the contracted part of the upper cone, at the point where the depression is greatest, a strong suction is brought about, which has the effect of carrying along the air between the wick and glass, and giving it its own velocity.  The draught of the two currents having been effected through the conical form of the upper part of the chimney, it remained to regulate the entrance of the external current into the flame.  If this current should enter the latter at too sharp an angle, it would carry it toward the mouth of the chimney before the chemical combustion of the carbon and oxygen was finished; and if, on the contrary, it should traverse it at too obtuse an angle, it would depress and contract it.  Experience has shown that in the majority of cases the most favorable angle at which the external current of air can be led into the flame varies between 35 deg. and 45 deg..  We say in the majority of cases, for there are exceptions; this depends upon the combustive materials and upon the conditions under which they enter the flame.  The annexed figure shows the form adopted by the inventor for oil and kerosene lamps.  As may be seen, the chimney consists of two cones, A and B, connected end to end by their small bases.  The upper one, A, or divergent cone, is constructed according to a variable angle, but one which, in order to produce its maximum effect, ought not to differ much from 5 deg..  This cone rests upon the convergent one, B, whose angle, as we have said, varies between 35 deg. and 45 deg..  To the large base of this cone there is soldered a cylindrical part, c, designed for fixing the chimney to the holder.  The height given the divergent cone is likewise variable, but a very beautiful light is obtained, when it is equal to six times the diameter of the contracted part.  When the lamp is designed to be used in a still atmosphere, free from abrupt currents of air, the height may be reduced to four times the diameter of the base, without the light being thereby rendered any the less bright.  As for the height to be given the convergent cone, B, that is determined by the opening of the angle according to which it has been constructed.  Finally, as a general thing, the diameter of the small base should be equal to half the large base of the convergent cone, B.