SkEY.— On the Cause of the Deposition of Camphor towards Light. 411 
hydrated to an equal extent with the salt which is separated thereby. It is 
just probable, too, that such a salt must be in a crystallized form. 
2. That in all those cases where substances other than the salt of which 
such solution is made are nuclear thereto, they act for this in an indirect 
manner, the first step being a removal of water from such solution, and this 
causes a portion of salt to separate—to form in its turn a nucleus capable 
of acting directly on the solution. Nuclear action is therefore, in these 
cases, always a result of secondary action, 
Arr. LXIV.—On the Cause of the Deposition of Camphor towards Light. 
By Wirunx Srey, Analyst to the Geological Survey Department. 
[Read before the Wellington Philosophical Society, 21st February, 1880.] 
Ir has often been observed that when camphor has long been kept in a 
glass bottle which is not evenly exposed to light, it detaches in part from 
the bulk to enerust with erystals that side of the bottle which is ** most 
exposed to light." This partiality of camphor for the more illuminated 
surface is ascribed, as I take it, to an effect of light as an etherial undula- 
tion distinct from that of heat possibly electrical. 
However, a few experiments which I made in this matter, show very 
clearly that sublimation and condensation (as produced by heat and cold 
respectively) are the sole cause of this kind of deposition. The whole matter 
turns upon the diathermacy of the glass of the bottle used : though exposed 
to light most, it warms but slowly and up to but a little way in the thermo- 
metric scale. The camphor, however, absorbs the heat thus transmitted by 
the glass, and the vapours formed thereby condense thereon, but for them 
to select that side * most exposed to light" it is necessary that there be 
upon or near to the other (the further side) some body absorbent of heat, so 
that by its conduction therefrom, via the air, to this side, its temperature 
may be raised to a higher degree than that of the other side, a circumstance 
of course always obtaining in those cases where camphor is deposited 
towards light. If no such kind of back-ground is present the camphor 
deposits most upon that side of the bottle which is the furthest away from 
light. 
In all probability the indications of weather got, or supposed to be got, 
by the use of “ camphor storm-glasses,” are also produced not by electrical 
or actinic action, or by light and heat in conjunction, as Dr. Parrion 
suggests, but by variation of temperature only. 
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