Mr. W. R. Birt on Atmospheric Waves. 487 



middle observation of each day ; at those stations where only two 

 are given morning and evening; I have taken a mean of them. 

 These observations I have so arranged as to exhibit the distribu- 

 tion of pressure over tlie area for eacli day — the line or lines of 

 the greatest diminution of pressure — and the relation of such dis- 

 tribution and of such lines to the aerial currents or winds. As a 

 convenient method of readily expressing these various relations 

 and giving to the discussion that completeness which otherwise it 

 would want, I have adopted the wave hypothesis, and to every line of 

 barometric maxima applied the term crest and to every line of minima 

 the term froi/gh. In a word, I have regarded the progress of the ba- 

 rometric and anemonal phaenomena as the progress of waves. The 

 observations remain the same both in Mr. Brown's and my own dis- 

 cussions, the results only are different ; and it remains for other 

 philosophers, by more closely investigating the s\ibject, and submit- 

 ting the observations to a more rigorous and searching discussion, 

 to advance this interesting inquiry and to become more intimately 

 acquainted with the causes of these interesting phaenomena. 



In addition to the discussion of these observations making us 

 acquainted with several large waves similar in character to the defi- 

 nition before given, it also reveals to us the arrangement of the aerial 

 currents with respect to such waves, or rather by means of these 

 observations and the plates accompanying them, we are able to 

 ascertain, not only the general direction of the aerial currents, but 

 also the barometric phaenomena resulting from their transit. 



Prof. Dove, in his second letter to Col. Sabine relative to the 

 magnetical and meteorological observations, has announced his 

 opinion that the equipoise of the atmosphere is maintained in the 

 temperate zone by currents oti the same level flowing iii ojjjwsite 

 directions* ; thus we have a bed or stratum of air moving from 

 the S.W., and on each side of this are strata of N.E. winds. We 



Fig. 2. 



♦ Report of the Fifteenth Meeting of the Britibli Association for the Advance- 

 ment of fjcieuce, p. Ul. 



