to alcohol is correct, the
resin is precipitated so finely as to elude the highest microscopic
power. By reflected light, such a medium appears bluish, by
transmitted light yellowish, which latter colour, by augmenting the
quantity of the precipitate, can be caused to pass into orange or red.

But the development of colour in the attenuated nitrite-of-amyl vapour
is doubtless more similar to what takes place in our atmosphere. The
blue, moreover, is far purer and more sky-like than that obtained from
Bruecke's turbid medium. Never, even in the skies of the Alps, have I
seen a richer or a purer blue than that attainable by a suitable
disposition of the light falling upon the precipitated vapour.

Iodide of Allyl.--Among the liquids hitherto subjected to the
concentrated electric light, iodide of allyl, in point of rapidity and
intensity of action, comes next to the nitrite of amyl. With the
iodide I have employed both oxygen and hydrogen, as well as air, as a
vehicle, and found the effect in all cases substantially the same. The
cloud-column here was exquisitely beautiful. It revolved round the
axis of the decomposing beam; it was nipped at certain places like an
hour-glass, and round the two bells of the glass delicate
cloud-filaments twisted themselves in spirals. It also folded itself
into convolutions resembling those of shells. In certain conditions
of the atmosphere in the Alps I have often observed clouds of a
special pearly lustre; when hydrogen was made the vehicle of the
iodide-of allyl vapour a similar lustre was most exquisitely shown.
With a suitable disposition of the light, the purple hue of
iodine-vapour came out very strongly in the tube.

The remark already made, as to the bearing of the decomposition of
nitrite of amyl by light on the question of molecular absorption,
applies here also; for were the absorption the work of the molecule as
a whole, the iodine would not be dislodged from the allyl with which
it is combined. The non-synchronism of iodine with the waves of
obscure heat is illustrated by its marvellous transparency to such
heat. May not its synchronism with the waves of light in the present
instance be the cause of its divorce from the allyl?

Iodide of Isopropyl.--The action of light upon the vapour of this
liquid is, at first, more languid than upon iodide of allyl; indeed
many beautiful reactions may be overlooked, in consequence of this
languor at the commencement. After so