4 IKE FORMS OF WATER IN 



water. The liquid particles thus produced form a kind 

 of water-dust of exceeding fineness, which floats in the 

 air, and is called a cloud. 



8. Watch the cloud-banner from the funnel of a 

 running locomotive ; you see it growing gradually less 

 dense. It finally melts away altogether, and if you 

 continue your observations you will not fail to notice 

 that the speed of its disappearance depends upon the 

 character of the day. In humid weather the cloud 

 hangs long and lazily in the air ; in dry weather it is 

 rapidly licked up. What has become of it? It has 

 been reconverted into true invisible vapour. 



9. The drier the air, and the hotter the air, the 

 greater is the amount of cloud which can be thus dis- 

 solved in it. When the cloud first forms, its quantity 

 is far greater than the air is able to maintain in an in- 

 visible state. But as the cloud mixes gradually with a 

 larger mass of air it is more and more dissolved, and 

 finally passes altogether from the condition of a finely- 

 divided liquid into that of transparent vapour or gas. 



10. Make the lid of a kettle air-tight, and permit 

 the steam to issue from the pipe ; a cloud is precipitated 

 in all respects similar to that issuing from the funnel of 

 the locomotive. 



11. Permit the steam as it issues from the pipe tc 

 pass through the flame of a spirit-lamp, the cloud is in- 

 stantly dissolved by the heat, and is not again precipi- 

 tated. With a special boiler and a special nozzle the 



