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III. Microscopic Observations on the so-called Vesicular Vapours of Water, as existing 
in the Vapours of Steam , and in Clouds, &fc. By A. Waller, Esq., M.JJ. 
Communicated by P. M. Roget, 31. D., Sec. R.S. 
Received April 13, — Read June 18, 1846. 
In a paper published in the Philosophical Magazine, February 1846, respecting some 
molecular actions of crystalline particles, I endeavoured to explain the fixation of 
particles of mercury, and the consequent formation of images in the Daguerreotype 
process. My experiments led me at that time to the conclusion, that the vapours, or 
rather fumes of condensed steam, consist of minute globules or spherules of water, 
and not of small vesicles according to the theory universally received at present, and 
expressed by the term of vesicular vapour. 
My opinion on this point was founded on the results obtained by microscopic in- 
spection of the condensed vapours of mercury and of other bodies, at the same time 
I stated that I was unable in the case of water to confirm it by direct observation. 
Subsequently, however, I have succeeded in doing so, and propose to show from the 
following observations that the opinions entertained respecting vesicular particles of 
water are completely erroneous. But before I describe my own experiments, I think 
it proper to state some of the ideas of our predecessors in science on vapours of 
water, and likewise the grounds on which they supported them. 
Sir Isaac Newton, on various occasions in his Optics, mentions the particles com- 
posing clouds, fogs and mists, &c., so as to leave no doubt that he considered them 
to be composed of minute globules or spherules, as may be seen in the following 
passages : — “ Between the parts of opaque and coloured bodies, are many spaces 
either empty or replenished with mediums of other densities; as water between the 
tinging corpuscles wherewith any liquor is impregnated, air between the aqueous 
globules that constitute clouds and mists.” — Prop. III. Book 2nd. “But when in order 
to compose drops of rain they begin to coalesce and constitute globules of all inter- 
mediate sizes, these globules, when they become of a convenient size to reflect some 
colours and transmit others, may constitute clouds of various colours according to 
their sizes. And I see not what can be rationally conceived in so transparent a sub- 
stance as water for the production of these colours, besides the various sizes of its fluid 
and globular particles.” — Prop. V. In noticing the coloured areola surrounding the 
sun and moon in certain circumstances, he does not fail, when giving the measurement 
of their diameters, to mention the way in which they may be applied in obtaining a 
knowledge of the relative diameters of the globules of water which give rise to them. 
