ON THE SO-CALLED VESICULAR VAPOURS OF WATER, ETC. 
25 
taneous and not successive, as is required. These appearances are easily explained 
in the present state of science, which could not be done in the time of Kratzenstein. 
The condensation of the vapours of water is caused by the sudden demand for 
caloric by the rarefied air in the glass globe, and the same takes place in the receiver 
of the pneumatic machine when there is a commencement of a vacuum. As the gas 
within recovers its caloric from surrounding bodies, the globular vapours and the 
moisture deposited on the inner surface of the glass recover their elastic condition. 
With regard to the colours observed, they are owing to the diffraction of light by the 
particles in suspension, and more particularly by those parts condensed on the sides 
of the glass, as in some of Fraunhofer’s experiments. Therefore it is in no manner 
possible to connect these colours either with the thickness of the vesicles, or with the 
vesicular theory. 
I have related these experiments thus fully, because I find that even at the present 
day, they still pass current with observers of a deservedly high reputation. Thus 
they are reproduced in Kaemtz’s Treatise on Meteorology, perhaps the most pro- 
found work on the science, and now rendered popular in this country by Mr. 
Walker’s translation of his Manual. 
De Saussure, on examining with a lens of an inch focus the steam of water floating 
over a dark surface, in speaking of the vesicles, says, “ La legerete de ces petites 
spheres, leur blancheur, leur apparence absoluinent differente de celles des globules 
solides, leur parfaite ressemblance avec lesbulles volumineuses que l’on voit nager a 
la surface du liquide ne laissent aucun doute sur leur nature ; il suffit de les voir 
pour etre convaincu que ce sont des spheres creuses, semblable a la grosseur pres a 
cedes que l’on forme avec l’eau de savon.” He further states that he confirmed these 
ideas by the examination of fogs or clouds on high mountains, when he was enabled 
to perceive in the same way minute vesicles, sometimes accompanied with drops or 
globules of water. He estimates the smallest at 4 /oo th of an inch, and the largest 
at arVofh. When these vesicles came in contact, they burst and formed a small 
drop of water. These experiments have been adopted and reproduced by most 
modern authors, among whom may be mentioned Berzelius, Fresnel, Mitscher- 
LICH, &C. 
As I have already stated in the Philosophical Magazine, I had an opportunity of 
repeating De Saussure’s observations on the clouds, at the Monastery of St. Bernard. 
I will quote the passage : “ Globules of various sizes are frequently discerned by the 
naked eye floating in all directions. I have endeavoured to ascertain their vesicular 
structure, but have been unable to do so from direct observations. It is frequently 
a most difficult point in microscopic investigation to decide upon the existence of a 
thin transparent membrane. It is still more so to pronounce upon the vesicular or 
spherular structure of globules in constant agitation ; and I believe that if minute 
spherules and vesicles could be mixed together, we do not possess any means at 
present of distinguishing them. I have never been able to detect that appearance 
MDCCCXLVII. p 
