Barometric Wave of November. 357 



years, are exhibited in Plate III. which accompanies this com- 

 munication. This Plate illustrated my Report on Atmospheric 

 Waves presented to the British Association for the Advance- 

 ment of Science at the Cambridge meeting in 184*5, and to 

 this and my preceding report in the volume for 1844 the 

 reader is referred for further information respecting this par- 

 ticular wave, and also on the subject of atmospheric waves 

 generally. Since my second report was presented to the As- 

 sociation the great wave has been again observed, and the 

 comparison of the curves for 1842, 1843, 1844, and 1845 has 

 suggested the idea that we have obtained the type of the baro- 

 metric oscillations during the middle portion of November. 

 This type has been expressed in the following language: — 

 " That during fourteen days in November, more or less equally 

 disposed about the middle of the month, the oscillations of the 

 barometer exhibit a remarkably symmetrical character; that 

 is to say, the fall succeeding the transit of the maximum or 

 highest reading designated by the word crest in the Plate, is 

 to a great extent similar to the preceding rise. This rise and 

 fall is not continuous or unbroken; in three out of four of the 

 occasions on which it has been observed, it has been found to 

 consist of Jive distinct elevations. The complete rise and fall 

 has been termed the great symmetrical barometric wave of 

 November, and as such has been considered to result from the 

 transit of a large wave ; but there is great reason to believe 

 that while it may be due to the transit of a normal wave of 

 about fourteen days' amplitude, it also exhibits the transits of 

 Jive secondary superposed waves. At the setting in of the 

 great November wave the barometer is generally low, some- 

 times below twenty-nine inches. This depression is succeeded 

 by two well-marked undulations, varying from one to two days 

 in duration. The central undulation, which also forms the 

 apex of the great wave, is of larger extent, occupying from 

 three to five days; when this has passed, two smaller undula- 

 tions corresponding to those at the commencement of the wave 

 make their appearance, and at the close of the last the wave 

 terminates." 



It is important to bear in mind that the symmetrical cha- 

 racter of the wave is coiifined to a certain line of greatest sym- 

 metry, and that at stations on each side of this line the sym- 

 metry is more or less departed from, according to their distance 

 from or proximity to it. It is also important to notice that 

 this line of greatest symmetry possesses an erratic character. 

 In the year 1842 it stretched from Dublin to Munich, Bir- 

 mingham and Brussels being two important stations on it. 

 Last year it appeared to be confined to the south of England ; 



