4]iS Mr, Si/hester on the Motions produced by the [June, 



subsidence of different precipitates shows a striking difference 

 either in the specific gravities or the size of the particles. The 

 earths and their insohible salts are longer subsidmg than those 

 of the metals, and the latier subside quicker as their specific 

 gravities are greater. We hence are enabled to explain how 

 large quantities of matter may exist in the atmosphere and in 

 other fiuids apparently in a state of suspension, but in reahty 

 falling with a velocity inversely proportionate to their size and 

 specific gravities. This in the atmosphere is visible to the eye, 

 when viewed in a sun-beam, and is principally animal and vege- 

 table matter. This explains the cause of the air becoming con- 

 taminated when heated to a temperature approaching to a red 

 heat at which the foreign matter is decomposed. 



We are also enabled to account for the aqueous matter in the 

 atmosphere in the form of clouds; this has formerly been supposed 

 in a state of suspension in some intermediate form between water 

 and vapour : this as well as the visible matter observed when 

 aqueous vapour is condensed, is nothing more than globules of 

 real water, there being no intermediate state between real water 

 and its elastic invisible vapour. Hence v.e have frequently in 

 the atmosphere spherical masses of real water from the size of 

 the largest drops of rain to those which are so minute as not to 

 reflect light sufficient to make them visible. 



Supposing steam or water in the elastic form (which can exist 

 at all temperatures) to consist of distinct atoms, each surrounded 

 by an atmosphere of caloric, the smallest particle which could 

 exist in the state of water, would consist of two individual atoms, 

 the next three atoms, and so on till the particle becomes 

 visible. 



The first appearance of condensation is a slight opacity, which 

 soon becomes whiter, as is observed in mist or fog. As the par- 

 ticles become larger, they fall with more rapidity, and assume a 

 darker colour, as is observed in various states of clouds. By 

 having recourse to the formula above given, we may form some 

 idea of the size of the globules of water to give an appear- 

 ance of their being suspended, in which state clouds have been 

 supposed to exist. In this case, as before, we put x = the 

 diameter of a particle, or globule of water. 



What must be the diameter of a globule of water to fall at the 

 rate of one inch per second after it acquires a uniform velocity? 



Here v =? 1 inch. 



/=T^a =-00119. 

 g = lO-T^.- 



1j = 1. 



B -/= -9988. 

 X = -JJ^- = " - " " •"'""' ■ = -000001164 inches. 



16 ^(B-/) IG X 16 X 12 X -9988 



When the body is of less specific gravity than the liquid, it 

 rises as a cork rises in water \ although in these cases a principle 



