gling with the flame,
and round its rim, were seen curious wreaths of darkness resembling an
intensely black smoke. On placing the flame at some distance below
the beam, the same dark masses stormed upwards. They were blacker
than the blackest smoke ever seen issuing from the funnel of a
steamer; and their resemblance to smoke was so perfect as to prompt
the conclusion that the apparently pure flame of the alcohol-lamp
required but a beam of sufficient intensity to reveal its clouds of
liberated carbon.

But is the blackness smoke? This question presented itself in a
moment, and was thus answered: A red-hot poker was placed underneath
the beam; from it the black wreaths also ascended. A large hydrogen
flame, which emits no smoke, was next employed, and it also produced
with augmented copiousness those whirling masses of darkness. Smoke
being out of the question, what is the blackness? It is simply that
of stellar space; that is to say, blackness resulting from the absence
from the track of the beam of all matter competent to scatter its
light. When the flame was placed below the beam, the floating matter
was destroyed in situ; and the heated air, freed from this matter,
rose into the beam, jostled aside the illuminated particles, and
substituted for their light the darkness due to its own perfect
transparency. Nothing could more forcibly illustrate the invisibility
of the agent which renders all things visible. The beam crossed,
unseen, the black chasm formed by the transparent air, while, at both
sides of the gap, the thick-strewn particles shone out like a luminous
solid under the powerful illumination. [Footnote: See Fragment: 'On
Dust and Disease', vol. i.]

*****

Supposing an infusion intrinsically barren, but readily susceptible of
putrefaction when exposed to common air, to be brought into contact
with this unilluminable air, what would be the result? It would never
putrefy. It might, however, be urged that the air is spoiled by its
violent calcination. Oxygen passed through a spirit-lamp flame is, it
may be thought, no longer the oxygen suitable for the development and
maintenance of life. We have an easy escape from this difficulty,
which is based, however, upon the unproved assumption that the air has
been affected by the flame. Let a condensed beam be sent through a
large flask or bolthead containing common air. The track of the beam
is seen within the flask--the dust revealing the light,