446 Miscellaneous Intelligence. 
Crimson.—Infusion of madder and cochineal. 
Black.—Japan ink thickened with gum. 
Green.—Equal parts of alum and blue vitriol with a few drops 
of muriate of iron. 
Milk White.—A crystal of alum held over a glass containing 
ammonia, the vapour of which precipitates the alumina on its 
surface. her: 
lll. Natura History. 
1. On the Suspension of Clouds, by M. Gay-Lussac.—Clouds 
are collections of aqueous vesicles, on the nature of which 
philosophers are not perfectly agreed. These vesicles may be 
either hollow or full. In the first case, though they must cer- 
tainly be more dense than the air they displace, we may conceive 
their suspension in this fluid, as we conceive of a heavy preci- 
pitate in water; but in the second case, we have more difficulty, 
in admitting that bodies ten or twelve hundred times heavier 
than the air they displace at the height of clouds should not 
precipitate towards the surface of the earth, and that the prin- 
cipal mass of clouds should be sustained at a height between 
1500 and 2500 metres. Even in admitting that the vesicles 
are hollow, their suspension is not exempt from difficulty; but 
not wishing to enter into discussion on the causes, I will con- 
fine myself to the consideration of the principal one, and endea- 
vour to show its importance by the ancient but curious experi- 
ment of soap bubbles. 
If the thinnest soap bubble be blown in an apartment it will 
never rise, but descend directly it is left to its own weight, and 
that even when it is not blown with air from the lungs, which is 
a little heavier than the atmosphere from carbonic acid in it*. 
But if, on the contrary, the soap bubble be blown in the open 
air above a heated soil, it will be seen to rise a height more or 
less considerable, and frequently break before it has attained 
that to which it would have reached, if its envelope had not been 
dissolved and thinned by the air. It is evident from this ex- 
periment, that there rises from the surface of the earth an ascend- 
ing current, which pushes the bubble before it, until weakened 
by its dilatation or by its mixture with colder air, its force of 
impulsion is in equilibrium with the weight of the soap bubble ; 
and we may conceive from that, why the latter cannot rise in an 
apartment where the temperature is uniform. If the bubble were 
* The bubble would descend even though the weight of the envelope 
could be removed, because being cooled by evaporation, the air within, 
notwithstanding the presence of aqueous vapour, would generally be 
heavier than the surrounding atmosphere.—Enp. 
