132 Mr. W. R. Birt on At nw spheric Waves. 



cality to another in certain given directions^ that should engage 

 the closest attention of the meteorologist as benis: at the root of 

 all our atmospheric movements, and intimately connected with 

 the origin of cyclones and atmospheric waves. The constant 

 relation existing between the direction of the wind and regions 

 of high and low pressures so well expressed by the crests, troughs, 

 and slopes of atmospheric waves, is but a stepping-stone to a 

 still higher generalization which may be arrived at when, in 

 addition to the heights of the barometer and the direction and 

 force of wind^ the temperatures at each station shall be discussed 

 with them. The elasticity of the air at any given moment is a 

 resultant of its temperature modified by the presence of aqueous 

 vapour; and for arriving at such higher generalization these 

 weather-elements, temperature and moisture, should be examined 

 daily during a specified period. 



Table IT. — Distribution of Pressure and AVind over the North- 

 west of Europe on April 2'2, 1872. 



First or lowest zone next above posterior trough. S.W. wave. 



Force. 



5 



5 



4 



-4 



+ 6 



+ 8 



This zone cuts the point of greatest depression (Scilly, 28-87), 

 which was probably in the trough of both waves. The S.W. 

 winds existed on the S.E. of this pointy and the N.E. winds on 

 the X.^V., with increasing pressures in each direction. 



Second zone above the post erio'^ trough. S.W. wave. 



Plymouth . . 28-97-0-34 S. -4 



Pembroke . . 29-01 -0*42 N.N.E. 6 



The trough of the X.AT. wave between these stations; wind at 

 Plymouth changed from E. to S. 



Third zone above the posterior trough. S.AV. wave. 



Portsmouth . 29-15 -O'OG S.S.W. -5 



Plolvhead . . 29-14--0-37 E. -3 



Greencastle . 29-40-0-30 E.X.E. 6 



Trough of N."\T. wave between Portsmouth and Holyhead. 

 The E. wind at Holyhead was cyclonic around the area of least 

 pressure. The anterior slope of the advancing \vave was charac- 

 terized bv the irreatest wind-force. 





Barom. 



Direction. 



Biarritz . . 



29-36-001 



s.w. 



Eochefort . . 



29-30 4-0-04 



s.w. 



L'Orient . . 



29-13-0-08 



w.s.w. 



Scilly . . . 



28-87-0-43 



AY.X.W. 



Boche^s Point . 



29-06-0-46 



N.N.E. 



Valencia . . 



29-25 -0-35 



N.N.E. 



