SOME WORLD'S WEATHER PROBLEMS 



By WILLIAM J. S. LOCKYER, M.A., Ph.D., F.R.A.S. 



Ce que nous connaissons est peu de chose, mais ce que nous ignorons est 

 immense. — Laplace. 



A popular writer once said, " The earth we inhabit is sur- 

 rounded by an atmosphere of air, the height of which is known 

 to be at least forty-five miles. It presses upon the earth with 

 a weight equal, at the level of the sea, to about fifteen pounds on 

 every square inch of surface. As we ascend high mountains, 

 this weight becomes less ; as we go down into deep mines, 

 it becomes sensibly greater. We breathe this atmospheric air, 

 and without it we could not live many moments. It floats 

 around the earth, being in perpetual motion ; and, according 

 to the swiftness with which it moves, it produces gentle breezes, 

 high winds, or terrible tornadoes." 



In these few words we have a very good general definition 

 of the aerial envelope surrounding our earth, and it is this 

 atmosphere and some of its movements which form the subject 

 of the present article. 



Many of us, I think, are rather apt to consider the height 

 of our atmosphere in relation to the size of the earth greater 

 than it really is. Although there is no real limit to its boundary, 

 we must still remember that the loftiest mountain peak rides 

 above about three-quarters of its total amount (by weight), 

 while the highest altitudes permanently inhabited by man have 

 still about half the atmosphere below them. If therefore we 

 were to draw a circle to represent the figure of the earth, 

 we should only have to increase the radius by about one- 

 thousandth part in order to include half the atmosphere. As 

 the circumference of the earth is about 24,000 miles, it will be 

 seen therefore that the greater aerial movements must take 

 place, for the most part, in a direction parallel to the earth's 

 surface, since the depth of the atmosphere is, comparatively 

 speaking, so restricted. 



Even at the break of the twentieth century it is nevertheless 



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