[Read before the Wellington Philosophical Society, 21st February, 1880.]

It 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 encrust with crystals 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 undulation 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 thermometric 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.