order to interrupt the ascending currents that are formed in proximity
to the body, the operation should be performed over a table, as shown
in the figure. The rings that pass beyond the table are not
perceptibly influenced by currents of hot air. A tube ¾ inch in
diameter, made by rolling up a sheet of common letter paper, suffices
for making very beautiful rings of one inch or more in diameter. In
order to observe the rings well, it is well to project them toward the
darkest part of the room, or toward the black table, if the operator
is seated. The first puffs will not produce any rings if the tube has
not previously been filled with smoke. The whirling motion is
perfectly visible on the exit of the ring from the tube, and even far
beyond.

[Illustration: FIGS. 2, 3, AND 4.--VARIOUS ASPECTS OF
SMOKE RINGS.]

As for the aspect of the rings projected with more or less velocity
to different distances from the tube, Figs. 2, 3, and 4 give quite a
clear idea of that. Figs. 3 and 6 show the mode of destruction of the
rings when the air is still. There are always filaments of smoke that
fall after being preceded by a sort of cup. These capricious forms of
smoke, in spreading through a calm atmosphere, are especially very
apparent when the rays of the sun enter the room. Very similar ones
may be obtained in a liquid whose transparency is interfered with by
producing a precipitate or rings in it.--_La Nature._

[Illustration: FIGS. 5 AND 6..--SMOKE RINGS BREAKING UP.]

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