Mr. W. R. Birt on Atmospheric Waves, 135 



Third zone ahc 



IV e trough, posterior 



slope. S.W. wave. 





Barom. 



Direction. Force. 



Brussels 



. 29'50 + 0-18 



—4 



Yarmouth . 



. 29-38 + 0-11 



S.S.E. 4 



Scarborough 



. 29-32 + 007 



S.S.E. +3 



Shields 



. 29-32 + 0-04 



E. -3 



Leith . . 



. 29-31-0-11 



E. -4 



Aberdeen . 



. 29-39-0-12 



E. -3 



Nairn . . 



. 29-39-0-21 



E.. -2 



^Yick . . 



. 29-46- 0-22 



E. -4 



Thurso 



. 29-46 -0-21 



E. -2 



Trough of N.W. 



wave between Scarborough and Shields. 



Lowest barometer at Leith 



Fourth zone above trough, posterior slope. S.W. luave, 

 Helder . . . 29-43 . 3 



Fifth zone above trough, posterior slope. S.W. wave. 



Cuxhaven . . 



29-54 + 0-21 



S.E. 



2 



0x0. . . . 



29-56 + 0-04 



N.E. 



4 



Skudesnaes 



29-52-0-04 



E.N.E. 



-2 



Christiansund . 



29-52-0-28 



N.E. 



+ 2 



Trough of N.W. wave S.E. of Oxo. 



A very important point to investigate in such inquiries as 

 these, has reference to changes of elasticity in large bodies of 

 air, such as occurred on the 20th and again on the 22nd per- 

 fectly independent of any progressive movement. Table V. 

 shows that the distribution of pressure and wind was much "the 

 same as on the 22nd, but that during the twenty-four hours 

 elapsed from 8 a.m. of the 22nd to 8 a.m. of the 23rd the 

 trough of the S.W. wave had advanced but a very short distance 

 towards the N.E. from its locality on the 22nd — also that the 

 trough of the N.W. wave occupied nearly the same locality as 

 it did on the 22nd, having rather receded towards the N.W. 

 than otherwise. The most remarkable feature is that the ante- 

 rior slope of the should-be advancing N.W. wave suffered a 

 diminution of elasticity which resulted in a. fall of the barometer 

 at all stations N.W. of a line joining Cape Clear and a point 

 between Oxo and Skudesnaes, which is exactly the reverse of 

 the phenomena presented by the anterior slope of an atmo- 

 spheric wave. This fall was accompanied by a diminution of 

 wind-foi'ce. At all stations S.E. of the line mentioned on the 

 posterior slope of the should-be receding N.W. wave, a rising ba- 

 rometer occuri'ed, with, at some stations, an increase of wind- 



