66 Iftature's /IIMraclee, 



tinue to ascend only until it reached a point 

 where the outside air and that contained in 

 the balloon are of the same density. If we 

 should send up this same balloon on different 

 days with the same rarefaction of internal air 

 we should find that on some days it would float 

 higher than others, because the density of the 

 air is constantly fluctuating, as is indicated 

 by the rise and fall of the barometer. Now 

 let us consider the balloon as a globule of 

 moisture of a definite weight, and this globule 

 only one of an aggregation of globules suffi- 

 cient to form a cloud. We can readily see 

 from what has gone before that a cloud thus 

 formed, having a definite density and weight, 

 would float higher some days than others. 



Assuming again that the density of the air 

 remains the same from day to day, the clouds 

 will still float high or low in the atmosphere 

 from another cause. Let us go back to our 

 illustration of the balloon. If we have a fixed 

 condition of atmosphere, external to the bal- 

 loon,' and vary the conditions internally, which 

 means varying its weight, the balloon will 

 float higher or lower as the internal conditions 

 are varied. Now apply this principle to the 

 moisture globules of which a cloud is formed 

 and we can understand why a cloud* will float 

 high or low from the two causes that we have 

 described. Clouds are of different color and 

 density, and this is due to the differences of 



