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XLV. An Inquiry into the Evidence on which the Theory of the 

 Circulation of the Atmosphere is based. By J. Knox Laugh- 

 ton, B.A., R.N* 



THE commonly received theory of the trade- winds and of the 

 circulation of air over the globe, which has been more 

 fully enunciated and more elaborately argued out by Captain 

 Maury than by any other writer, is, I conceive, open to very 

 grave objections. The diagrams are so simple, and the scheme 

 so complete in its details, that it obtains at once a ready assent 

 to its truth ; but further consideration leads to the question, 

 How is it possible for a body of air whose density is (in round 

 numbers) represented by 30 inches of mercury, to be forcibly 

 displaced by a body of air which has a density of only 29 inches ? 

 or, conversely, How can heavy air rise through light and form 

 an upper current above it ? When, then, we find it asserted that 

 such extraordinary transpositions do take place, whether in the 

 latitude of 30° N. or S., or at the poles, we are not unnaturally 

 led on to inquire into the evidence on which this assertion is 

 founded, and on which, in point of fact, the whole system must 

 be supposed to rest. 



A distinctive and important feature of the scheme is the as- 

 sumption that, between the tropics (or rather between the lati- 

 tudes of 40°) and the poles, the prevailing winds are westerly and 

 towards the pole ; that is to say, are from the south-west in the 

 northern, and from the north-west in the southern hemisphere. 

 This is distinctly laid down by Maury in his " Diagram of the 

 Winds" (Sailing Directions, vol. i. plate 3, eighth edition), as 

 well as in the accompanying text. His words are : — 



" From the parallel of 40° up toward the north pole the pre- 

 vailing winds are the south-west passage winds; these, in the 

 Atlantic, prevail over the easterly winds in the ratio of about two 

 to one. Now, if we suppose, and such is probably the case, these 

 westerly winds to convey in two days a greater volume of atmo- 

 sphere towards the arctic circle than those easterly winds can 

 bring back in one, we establish the necessity for an upper cur- 

 rent," &c. (Sailing Directions, vol. i. p. 41.) But is this state- 

 ment borne out by the evidence ? The following is the mean of 

 the observations tabulated by Howard (Climate of London, vol. i. 

 p. 75) during a period of seventeen years : — 



Between N. and W. 105 

 „ N. and E. 74 



Between S. and W. 

 „ S. and E. 



104 

 56 



or, more shortly, winds 



From the pole, Polar . . . . 179 

 To the pole, Equatorial . . 1G0 





* Communicatee 



by the Author. 





