small heavi/ Bodies in Ai), &c. 247 



But what is the number of these chimneys compared with 

 those of the metropolis ? What the quantity of coals used in 

 these, compared with what is used in those ? Those of the me- 

 tropolis must he stopped up, or compelled to burn their smoke 

 at the same time that these are interdicted, or compelled to 

 bum theirs. 



So objections were raised to the use of coal gas for the pur- 

 poses of illumination, from its supposed injurious effects upon 

 the health of the town, whilst every chimney in every house 

 in town, where the fire flamed and burned, was burning coal gas. 

 Noticing the foregoing inconsistencies, I have been induced to 

 think it would be useful and amusing by the instances adduced, to 

 develope the principles upon which the formation of vapours, and 

 floatage of bodies, even the heaviest, in the atmosphere, depend. 



In consequence of the attractions for water of the 

 materials which form the base of atmospheric air, and of 

 the heat upon which its gaseous state depends, water is dis- 

 solved in atmospheric air in given quantities at given tempera- 

 tures. The solution is transparent. Upon changes of tempe- 

 rature, particles of water begin to be detached from the solution, 

 in portions so very small, that their weights scarcely exceeding 

 the attractions of the air which dissolved them, they continue 

 to maintain their floatage in the form of clouds. When, by further 

 accession of particles, these masses are increased in size and 

 weight so as to overcome the attractions of the air acting prin- 

 cipally on surfaces which increase as the squares, whilst the 

 weights increase as the cubes of diameters, they are then preci- 

 pitated and fall to the earth as drops of rain. 



Water, exposed to the action of fire or heat in a given state of 

 accumulation, is readily dissolved therein, and forms with it a 

 transparent elastic gas, permanent at all temperatures above 

 212° of Fahrenheit, and called steam. In the steam, the par- 

 ticles of water are severally attracted by those of the heat sur- 

 rounding them, and being removed to distances from each 

 other, at which their mutual attractions cease, and those of the 

 heat alone prevail, thus constitute with boat an uniform com- 

 pountl body, permeable to light in all directions. When, by 



