Mr. W. R. Blrt on Atmospheric Waves. 485 



mena, and the term atmospheric wave has been used to designate 

 that ideal individualitij which the mind attributes to the process 

 wliich it observes of the successive change of place wliich the baro- 

 metric maxima and minima undergo, and by which they regularly 

 succeed each other over the area under examination; this ideal in- 

 dividuality has been employed as a mean ot examining the move- 

 ments just alluded to. 



Mr. Scott Russell, in his admirable report on waves, presented to 

 the British Association during its sitting at York in 1844, has given 

 the elements of an aqueous wave. These elements appear so clearly 

 to express the relations of the barometric phsenomena (simply con- 

 sidered as such), that I shall avail myself of Mr. Russell's terms to 

 indicate the distribution of pressure over the surface of the earth, as 

 in figure J. 



x» S-=r Fig. 1. 



W, The crest. w a. The amplitude. 



■"' -■ The front. W h, The height. 



W w, The back 



In reference to this figure, the line of high pressure stretching 

 across the area (the figure being supposed to cut this line transversely) 

 has been termed the cres/, W; the line of low pressure in advance of 

 the crest, the anterior troiigh, a (the origin of Mr. Scott Russell's 

 Avater wave) ; the line of low pressure succeeding the crest, the pos- 

 terior trough, IV (the end of Mr. Scott Russell's water wave) ; the line 

 w...h, as measured by the mercurial column, the altitude of the wave ; 

 the slope W a, the anterior slope or front of the wave ; the slope' 

 W w, the posterior slope or back of the wave; tu a constitutes the 



amplitude of the wave, and x x in the same direction, the axis 



of translation. 



The observations to which allusion has been made, were published 

 by Mr. William Brown in a paper that appeared in the Philosophical 

 Magazine for April 1 846. This paper is entitled " On the Oscillations 

 of the Barometer, with particular reference to the Meteorological 

 Phaenomena of November 1 842." The object of the author is to show 

 that the barometric oscillations are produced by the meeting of oppo- 

 site or nearly opposite aerial currenbi ; that one current thus meeting 

 or impinging on another, deflects it, and under some circumstances 

 produces a rise of the mercurial column, but under others occasions a 

 fall in many cases of considerable magnitude. In order to elucidate his 

 views, Mr. Brown has collected barometric observations from eleven 

 stations, which are scattered over an area included by the following 

 angular points: — The Orkneys, Christiania in Norway, Paris, Ply- 

 mouth and Cork. These observations are in most cases given as read 



* Mr. Scott Russeli designates tlic point a the origin; a better term I apprcliend 

 would be comvivncement. 



