Microscopic observations on the so-called vesicular vapours of water as existing in the vapours of steam, and in clouds, &c

From some experiments, of which the author published an account in the Philosophical Magazine of last February, he was led to conclude that the opaque vapours of condensed steam consist of minute globules or spherules of water, and not of small vesicles, as is implied in the generally received theory, according to which this condition of water is designated by the term vesicular vapour . In the present paper, he relates a set of experiments confirming by microscopic observation his views of the globular condition of the particles of opaque vapours; premising a short retrospect of the opinions of Sir Isaac Newton, Halley, Kratzenstein, and De Saussure on this subject. Finding it impossible to observe the globules with any high magnifying power while they are at liberty to move, the author adopted the plan of fixing the condensed vapours arising from the breath or other sources, in some liquid, such as oil, which has no affinity with water. Of the many vehicles which he has tried, he finds Canada balsam to be that which is best adapted for these observations. By breathing with a little force on a slip of glass previously covered with a thin layer of balsam, the vapours of the breath are not only condensed on its surface, but penetrate beneath, where they may be recognised in opaque streaks of a white colour, and where they remain stationary for more than an hour; or, if covered with another thin piece of glass or talc, for a much longer period. These streaks are decomposed under the microscope into minute globules perfectly spherical, like shot, or the globules of mercury. The author describes, at some length, the various appearances presented under different circumstances, and with different oily fluids; and gives drawings of these appearances as exhibited by the microscope.