26 
DR. A. WALLER’S MICROSCOPIC OBSERVATIONS 
of bursting of the globules mentioned by De Saussure, but sometimes when the 
agitation of the air is slight, two of the larger globules 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.” From the commencement of my experiments, I found that the greatest 
obstacle to a perfect investigation of these globules arose from their excessive mo- 
bility. Even to the naked eye this is very great, and is the cause of several optica] 
delusions ; but by the use of magnifying instruments, this mobility must necessarily 
be increased in proportion to their power. With the simple microscope of De Saus- 
sure, a globule might occasionally be perceived, and its diameter estimated to a 
certain extent ; but with the compound achromatic microscope I employ, their angular 
displacement is too rapid to form any correct sensation on the retina. For this 
reason I was led to adopt the plan of fixing the condensed vapours arising from the 
breath or other sources, in some liquid which, like oil, possesses no affinity for water. 
The liquids with which I thus mixed the vapours of water were very numerous; and 
as the appearances thus presented under the microscope were not the same in all 
cases, I will only mention some of the most interesting. 
Canada balsam is, perhaps, of all other vehicles, the most adapted for these observa- 
tions. A slip of glass covered with a thin layer of it is to be used. By breathing on it 
with a little force, the vapours of the breath will not only be condensed on its surface, 
but will penetrate below T , where they may be easily recognized in opake streaks of a 
white colour. By reason of the viscousness of the balsam, they will remain almost 
stationary for more than an hour, and for a much longer period if covered with 
another thin piece of glass or talc. Under the microscope these streaks are decom- 
posed into minute globules perfectly spherular like shot, or the globules of mercury. 
See Plate II. fig. l.bb. Their sizes vary within certain limits, between which they occur, 
of all intermediate sizes. They agglomerate together in various ways, forming lines 
composed of several rows of them touching each other, but without any signs of 
coalescing, unless attentively examined for some time, when two smaller ones may 
be perceived to disappear, and in their place is seen another of larger size resulting 
from their fusion. A certain degree of attraction exists between them, as they are 
generally packed together as closely as possible, and any hiatus caused by any of 
them coalescing is quickly filled by others. Thus a group will sometimes have its form 
modified and reduced by their pressing inwards to supply any hiatus left after one 
or two have coalesced. Another proof of their mutual attraction is offered in the 
movement en masse of a single file of globules without their separating from each 
other. In favourable circumstances, I have found some of them still in “ statu quo” 
after a lapse of twenty-four hours or more. Their diameters vary generally from 
0-ooi mm to Q - 003 mm . They disappear at length by adhering to and wetting the surface 
of the glass above or below them, where they may easily escape notice, as from 
