[Illustration: FIG. 1--APPARATUS FOR PRODUCING RINGS OF SMOKE.]
When, by means of a tube of from 2 to 5 millimeters in diameter, we
gently blow tobacco smoke against a wet pane of glass, we produce very
fugitive rings. If we operate with a closed vessel the rings are fixed,
the current being itself uniform. But the experiment that shows the
phenomenon perfectly is the one that consists in rendering the current
automatic by means of an aspirator--an arrangement analogous to that
devised by Mr. Nickles for analyzing the flame of a candle. A tapering
glass tube or, better, a metallic blow pipe traverses a cork which
hermetically closes a large bottle having a cock beneath and filled
with water (Fig. 1). The nozzle of the blow pipe entering the center
of the flame, and the cock being open, the liquid flows, and a column
of white smoke descends vertically to the surface of the water, where
it forms several concentric rings whose relief soon increases with the
thickness of the heavy smoke, which finds no exit. These rings have a
diameter so much the greater in proportion as the current is stronger
(Fig. 2).
Unfortunately, the number of the rings soon diminishes in measure as
the stratum of smoke that remains upon the surface of the water becomes
thicker. Finally, there remains but a single ring, which has a
thickness in the center of more than 0.015 m. (Fig. 3).
[Illustration: FIGS. 2 TO 5.--DIFFERENT ASPECTS OF RINGS OF SMOKE.]
Instead of the smoke of a candle, we may employ that of a cigar or of
a tobacco pipe. We thus avoid a deposit of fatty matter, which, in the
first case, soon clogs up the tube, if it is too fine a one, and thus
puts a stop to the experiment.
Several circumstances are known under which rings or crowns are
produced. (1) For example, in the spontaneous combustion of
phosphureted hydrogen, the resulting white vapors of phosphuric acid
rise, and roll round in horizontal white crowns when the air is calm
(Fig. 4). These crowns, whose diameter keeps on increasing, end by
separating into strips that dissolve in the humidity of the air. (2)
The crowns that we sometimes observe in calm weather around cannons
at the moment of firing have the same origin, although they are of a
different nature, and spread horizontally to a certain distance. With
vertical howitzers the crowns are horizontal, and very beautiful when
seen from beneath, since they rise vertically. (3) As well known,
a cardboard box having two apertures in the center of two opposite
sides, when filled with smoke and struck upon one of these sides,
allows the escape through the opposite aperture of curling rings of
smoke. (4) Steam escaping into the open air, through the intermittence
of a vertical eduction pipe, sometimes makes its exit in the form of
circular or elliptical crowns.--_La Nature._