Hoar-frost is generally described as frozen dew, and is supposed to be deposited in the same manner and under the same conditions as dew; the only difference being in the temperature at which it is deposited. Though in a general way this may be so, yet there are certain differences in the conditions, and the manner in which the vapour is condensed at the different temperatures, which seem worth referring to.

This paper details an investigation undertaken to see the influence of certain rays of white light on root-absorption and assimilation in the vegetable kingdom. One of us has been for some years investigating a problem as to the use of ferrous sulphate as a plant food (see Dr Griffiths' memoirs in Journal of Chemical Society [Trans.], 1883, 1884, 1885, 1886, 1887). In the experiments to be detailed here, we have used ferrous sulphate as an indicator of root-absorption.

The composition of the ice produced in saline solutions, and more particularly in sea-water, has frequently been the object of investigation and of dispute. It might be thought that to a question of whether ice so formed does or does not contain salt, experiment would at once give a decisive answer. Yet, relying on experiment alone, competent authorities have given contradictory answers. All agree that ice, whether formed artificially in the laboratory by freezing sea-water, or found in nature as one of the varieties of sea-water ice, retains, in one form or another, and with great tenacity, some of the salt existing in solution in the water. The question at issue is whether this salt is to be attributed to the solid matter of the ice or to the liquor mechanically adhering to it, from which it is impossible to free it. Most bodies, and especially those which take a crystalline form, are easily purified and freed from all suspected foreign matter, with a view to analysis, by the simple operation of washing and drying. It is impossible to wash the crystals, formed by freezing a saline solution, with distilled water, because they melt at a temperature below that at which distilled water freezes.

In the regions of the Antarctic Ocean where icebergs are numerous, and where in winter the sea-water freezes, the distribution of temperature in the deeper layers of water is peculiar. The facts are detailed in the Challenger Narrative (vol. i.). The general result of her observations went to show that, from the edge of the ice-pack, a wedge of cold water stretches northwards for more than 12° of latitude, underlying and overlying strata at a higher temperature than itself (p. 418).