190 Dr. A. Waller's Observations on certain 



could be mixed together, we do not possess any means at pre- 

 sent of distinguishing them. 



I have never been able to detect that appearance of burst- 

 ing of the globules mentioned by De Saussure, but sometimes, 

 when the agitation of the air is slight, two of the larger glo- 

 bules may be seen floating towards each other, and afterwards 

 disappear suddenly, which may be explained, if we admit that 

 it is caused by the union of the two spherules into one, which 

 is too heavy to remain any longer in suspension, and whose 

 rapid deposition conceals it from the sight. 



There may be urged as objections to the vesicular theory, 

 that if the pellicle become extremely thin, the vesicle would 

 no longer be perceived any more than the apex of an air- 

 bubble before bursting, or the central black spot of a system 

 of Newton's coloured rings. It will be seen below that the 

 globules of vapour possess the power of depositing themselves 

 in a crystalline form, which requires a tranquil deposition of 

 particles, such as could scarcely be deemed possible, if the air 

 contained in each had to escape at the moment of its crystal- 

 lization. 



I have endeavoured to fix the globules of water on glass 

 and other substances, so as to be enabled to submit them to 

 microscopic inspection, but from their volatile nature and other 

 causes have not succeeded. However, it is easy to do so with 

 almost any other volatile substance; and I have examined 

 several in this way without detecting the slightest appearance 

 of a vesicular structure. Mercury is deposited under the 

 form of globular particles, with a metallic lustre whose dia- 

 meter is 3^jo tn °f a millimetre, m which I have never detected 

 any internal cavity by the most careful examination*. Flour 



* In order that others who may wish to verify these results may operate 

 in the same conditions as myself, it is proper to state that the mercurial 

 vapours were disengaged in a hox, such as is used in the Daguerreotype pro. 

 cess ; and after the mercury had been raised to a temperature of about 90° 

 centigrade, it was allowed to cool. Three experiments were made in this 

 manner: in the two first the glass plate was placed four inches above the 

 mercury, in the other it was eight inches distant. The appearance of the 

 globules was the same in each case ; if any difference existed in their size, 

 those of the last experiment were rather larger. In another experiment, 

 where a common Daguerreotype plate was substituted for one of glass, the 

 appearance of the globules was in all respects the same. From the manner 

 in which they are deposited, they appear to exert an influence over each 

 other, as they are frequently found in groups of three or four, or more, 

 Mr. Ross has stated on the part of Mr. Solly (Microscopical Society, De- 

 cember 1843), that these globules are deposited in hexagonal groups; but 

 with preconceived ideas no doubt it would be very easy to form such 

 shapes, as it would be to form triangles or any other simple geometrical 

 figure, particularly when the illusions inseparable from catoptric microscopy 



