634 SCIENTIFIC RECREATIONS. 



VAPOUR AND CLOUDS. 



Vapour, as we have heard, is invisible, and is produced by heat. As 

 the visible steam (which is invisible as it issues from the safety valve at the 

 actual aperture, and nearly invisible altogether on a hot day) is produced by 

 combustion, so vapour is produced by the heat of the sun's rays. But there 

 are some observations to be made respecting these rays, which arc the cause 

 of vapour, and therefore of cloud, rain, dew, frost, ice, snow, and water all 

 over the earth ; and we must look at the circumstances closely. 



Those who have followed us through this volume will remember that 

 at the end of Chapter VIII. we remarked upon the spectrum, and made a 

 few observations respecting the heat spectrum, and the velocity of light rays, 

 which became too rapid to be observed, and then they developed heat in- 

 visible heat produced by non-luminous waves, which proceed from the sun as 

 surely as visible rays or light. Professor Tyndall has written very pleasantly 

 upon this subject, and, with his clear leading, any reader can study for 

 himself. 



We have now arrived at the conclusion that there are visible and 

 invisible rays giving us respectively light and heat. These latter are the 

 means whereby the ice is melted, and by which water is evaporated to 

 vapour, and formed into CLOUDS when it is chilled or condensed. Here is 

 another link in the beautiful chain constructed by Nature. We cannot 

 penetrate far into any portion of the system of the universe without being 

 struck with the wondrous harmony that exists between every portion of it. 

 Thus heat and light, vapour, cloud, rain, dew, and ice are all intimately 

 connected. 



A cloud, then, is a visible body of vapour in the atmosphere, which is 

 supported by an invisible body of vapour. It will remain thus invisible so 

 long as the atmosphere is not saturated with moisture. The air can contain a 

 great quantity of moisture without its being rendered visible, and so when 

 the day is hot we see no steam from the locomotive. It is absorbed into 

 the dry atmosphere. But when the day is " damp " we find that the air 

 has nearly as much moisture as it can carry, and the steam is condensed, a 

 portion falling in tiny drops like rain. This is proved every day in cold 

 weather when ice is found in the windows the cold air has condensed and 

 frozen the water breathed out from our lungs, and snow has been known to 

 fall in a ball-room when a cold current of air was admitted. 



People are sometimes apt to think that if the sun were very hot, 

 glaciers, and such icy masses, would diminish ; but we think after what has 

 been said respecting the power of the sun's rays to evaporate water, all will 

 see that the contrary is the fact. Without sun-heat we should have no 

 cloud, and as clouds give us rain and snow and ice and glacier, we must 

 come quickly to the conclusion that glaciers and snow are the direct results of 

 the heat of the sun. The "light" rays of the sun do not penetrate snow, and 

 that is why our eyes are so affected in snowy regions. The poor Jeannette 



