the nucleus that at a certain humidity becomes the centre of condensation of the wa

cooled in a body below the dew-point; or a mass of warm and moist air rises into a mass which is cold and dry. The first forms a cloud, called, from being a layer, stratus; the second forms a cloud, called, from its heap appearanc

ner, like "mares' tails," receiving the name cirrus. When the cirrus and cumulus are combined, in well-defined roundish masses, what is familiarly de

those named above are the principal. In a beautiful sunset one can sometimes notice two or three distances of cloud

e of dust-particles which attract moisture on certain conditions, yet even twenty years ago he said that it was probabl

gly, he has carefully tested a few of the ordinary constituents and impurities in our atmosphere

rived of its dust-particles and exposed to sunshine, does not show any cloudy condensation on e

ne minute; the result was a considerable quantity of condensation, even with such a weak solution. When t

ei. Curious is it that sulphurous acid is puzzling to the experimentalist for cloud formation. It

ulphuretted hydrogen (which one always associates with the smell of r

tion to take place in certain circumstances in the absence of dust. This seems paradoxical in the light of the former beautiful experiments; but, in ordinary circumstances, dust is needed for the formation of clouds. However, supposing there is any part o

m cloudy condensation, whether the sun shines or not. These are produced

great boon to us on the earth; for it assures us of clouds being ever existing to defend us from the sun's ex