Mr. W. R. Birt on Atmospheric Waves. 493 



the south-westerly gusts prevailing, directi>«g the vane to that quar- 

 ter ; and the north-westerly immediately following, instantly occa- 

 sions a change carrying the vane towards the N.W. These sudden 

 and extensive changes are rendered more distinctly perceptible by 

 means of a small kite flown with about 250 or 300 feet of string, or 

 even more ; the distinctness and independence of the direction of 

 the two currents are readily seen, as well as the difference in their 

 strength. 



Discussion ofSlv. Brown's Observations. 



In the discussion to which I have alluded, I have first arranged 

 such of the observations collected bj' Mr. Brown, or deductions from 

 them, as indicate the barometric pressure about the middle of each 

 day at the stations before-named, as near as the data furnished by 

 that gentleman will allow. These observations or deductions will be 

 found in Table I. The arrangement is such that the eye may readily 

 ascertain tlie barometric state of the atmosphere at any station on 

 any day embraced by the area and period included in the table. 

 The changes at any one station are also readily seen, the altitudes 

 above 30 inches being distinguished from those between 29 and 30, 

 and those below 29 also being distinguished from the rest. This 

 table forms the basis of the conclusions which have been thus arrived 

 at. The values corresponding to each day have been arranged with 

 especial reference to the maximum and minimum of that day in 

 space, that is, the station exhibiting the greatest pressure on any 

 particular day has generally been placed first on the list for that 

 day ; and that exliibiting the least, last. At the head of each list 

 are placed the directions of the crests as indicated by the observa- 

 tions. Crests passing from N.W. to S.E. are distinguished by the 

 odd numbers, and those passing from S.W. to N.E. by the even. 

 When the observations give two slopes from a crest or trough pass- 

 ing between such slopes, the observations have been arranged to 

 exhibit this. After the arrangement of the observations, the lines 

 of tlie greatest diminution of pressure corresponding in a majority 

 of cases to tranverse sections of the waves, and exhibiting either 

 their anterior or posterior slopes, are inserted. These are succeeded 

 by the direction of the wind on each side of the crests as given in 

 ^Ir. Brown's plates, and the discussion of each day's observation is 

 concluded by a few explanatory notes*. 



* For the complete discussion of Mr. Brown's observations, the reader is re 

 ferred to the author's tliirrt report on atmos])heric waves in the llei)ort of the Six- 

 teenth Meeting of the Hritisii Association for tlie Advancement of Science, held at 

 Southampton in 1816, i)p. Ill to 162. 



