IN CLOUDS AND RIVERS, ICE AND GLACIERS. 



85 



every puff of the engine a cloud is projected 

 into the air. Watch the cloud sharply : you 

 notice that it first forms at a little distance 

 from the top of the funnel. Give close at- 

 tention and you will sometimes see a per- 

 fectly clear space between the funnel and the 

 cloud. Through that clear space the thing 

 which makes the cloud must pass. What, 

 then, is this thing which at one moment is 

 transparent and invisible, and at the next 

 moment visible as a dense opaque cloud ? 



7. It is the steam or xapor of water from 

 the boiler. Within the boiler this steam is 

 transparent and invisible ; but to keep it in 

 this invisible state a heat would be required 

 as great as that within the boiler. When the 

 vapor mingles with the cold air above the hot 

 funnel it ceases to be vapor. Every bit of 

 steam shrinks, when chilled, to a much more 

 minute particle of water. The liquid parti- 

 cles 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 fun- 

 nel of a running locomotive ; you see it 

 growing gradually less dense. It finally 

 nuilts away altogether, and it' 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 luis been 

 reconverted into true invisible vapor. 



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

 the greater is the amount of cloud which 

 can be thus dissolved in it. When the cloud 

 first forms, its quantity is far greater than the 

 air is able to maintain in an ^invisible stale. 

 But as the cloud mixes gradually with a 

 larger mass of air it is more an :1 more dis- 

 solved, and finally passes altogether from the 

 condition of a finely-divided liquid into that 

 of transparent vapor or gas. 



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

 permit the steam t^> issue from the pipe ; a 

 cloud is precipitated in all respects similar to 

 that issuing from the funnel of the locomo- 

 tive. 



11. Permit the steam as it issues from the 

 pipe to pass through the flame of a spirit- 

 lamp, the cloud is instantly dissolved by the 

 heat, and is not again precipitated. With a 

 special boiler and a special nozzle the exper- 

 iment may be made more striking, but not 

 more instructive, than with the kettle. 



12. Look to your bedroom windows when 

 the weather is very cold outside ; they some- 

 times stream with water derived from the 

 condensation of the aqueous vapor from your 

 own lungs. The windows of" railway car- 

 riages in winter show this condensation in a 

 striking manner. Tour cold water into a dry 

 drinking-glass on a summer's day : the out- 

 fci'iu surface of the glass becomes instantly 

 uunmccl by the precipitation of moisture. 

 On a warm day you notice no vapor in front 

 of your mouth, but on a cold day yi-u form 

 there a little cloud derived from ihe conden- 

 sation of the aqueous vapor from the hir^r. 



13. You may notice in a ball-room that as 

 long as the door and windows are kept, 

 closed, and the room remains hot, the air re- 

 mains clear ; but when the doors or windows 

 are opened a dimness is visible, caused by 

 the precipitation to fog of the aqueous vapor 

 of the ball-room. If the weather be intensely 

 cold the entrance of fresh air may even cause 

 now to fall. This has been observed in Rus- 

 sian ball-rooms ; and also in the subterranean 

 stables at Erzeroom, when the doors are 

 opened and the cold morning air is permitted 

 to enter. 



14. Even on the driest day this vapor is 

 never absent from our atmosphere. The 

 vapor diffused through the air of this room 

 may be congealed to hoar frost in your pres- 

 ence This is done by filling a vessel with, a 

 mixture of pounded ice and salt, which is 

 colder than the ice itself, and which, there- 

 fore, condenses and freezes the aqueous 

 vapor. The surface of the vessel is finally 

 coated with a frozen fur, so thick that it may 

 he scraped away and formed into a snow- 

 ball. 



15. To produce the cloud, in the case of 

 the locomotive and the kettle, heat is neces- 

 sary. By heating the wakr we first convert 

 it into steam. &n<l then, by chilling the steam 

 we convert it into cloud. Is there any file in 

 nature which produces the clouds of our at- 

 mosphere V There; is : the fire of the sun. 



10. Thus, by tracing backward, without 

 any break in ihe chain of occurrences, our 

 river from its end t its real beginnings, we 

 come at length to the sun. 



IT. There are, however, rivers which have 

 sources somewhat different from those just 

 mentioned. They do not begin by driblets 

 on a hill-side, nor can they be traced to a 

 spring. Go, for example, to the mouth of 

 the river Rhone, and trace it backward to 

 Lyons, where it turns to the cast. Bending 

 round by Chambery, you come at length to 

 the Lake of Geneva, from which the liver 

 rushes, and which } r ou might be disposed to 

 regard as the source of the Rhone. But go 

 to the head of ihe lake, and you find that 

 the Rhone there enteis it, that the lake is 

 in fact a kind of expansion of the liver. 

 Follow this upward ; you find it joined by 

 smaller rivers from the mountains right and 

 left. Pass these, and push your journey 

 higher still. You come at length to a lingo 

 mass of ice the end of a glacier which fills 

 the Rhone valley, and from the boiuuii of tiie 

 glacier the river rushes In the glacier of 

 the Rhone you thus find the souice of the 

 river Rhone. 



18. But again we have not reached the real 

 beginning of the river. You soon convince 

 yourself that this earliest water of the Rhone 

 is produced by the melting of the ice. You 

 get upon the glacier and walk upward along 

 it. After a time the ice disappears and you 

 come upon snow. If you are a competent 

 mountaineer you may go to the very top of 

 this great snow-field, and if you cross the top 



