486 Mr. W. R. Birt on Atmosjyheric Waves. 



off from tlie scale. In addition to these the paper is accompanied by 

 six plates, in which the direction of the wind at numerous stations ia 

 indicated for every day during twenty-six days in the month by 

 arrows. The anenional observations published in the body of the 

 paper not being in all cases for consecutive days, a comparison of 

 tliem with the plates is rendered difficult ; nevertheless the plates 

 form a very valuable portion of the communication, and if they have 

 been laid down from accurate observations, they furnish us with an 

 important addition to our knowledge of the ar/a«^e;HeM< of the aerial 

 currents, especially with respect to the distribution of pressure. It 

 is a matter of regret that Mr. Brown did not so arrange his obser- 

 vations and plates, that the accuracy of the latter could have been 

 seen by inspection. 



This paper is peculiarly interesting at the present time, when the 

 attention of meteorologists is directed to the important and interesting 

 problem of the barometric oscillations. I have already noticed the 

 views which have been taken of these oscillations as the results of 

 waves. In this paper they are regai'ded as the effects of currents ; 

 and it appears that meteorologists are now divided as to which of 

 these hypotheses they shall be referred. Professor Dove remarks, 

 in his letter to Colonel Sabine on the Magnetical and Meteorological 

 observations*, "the so-called irregular variations of the barometer 

 are regarded by some persons as only tiie effects of currents of air of 

 unequal temperature and moisture ; other persons distinguish the 

 effects of currents from the effect of undulations progressing in the 

 manner of ivaves of sound, and propagating themselves with great 

 velocity over large portions of ike eartiis surface." 



It is Avorthy of notice, that these movements have been referred 

 to two very distinct kinds of waves. Prof. Forbes speaks of them 

 as great atmospheric tidal waves, and Prof. Dove speaks of a class 

 of individuals who regard them as progressing in the manner of 

 waves of sound. 



It is not my intention to enter into an examination of the conclu- 

 sions and results which Mr. Brown has arrived at; as the question is 

 open, I apprehend I have not conmiitted an injustice towards that 

 gentleman by having employed a rather different process to that 

 which he has used, and further discussed the observations he has 

 given. I beg to acknowledge the obligations I am under to him 

 for these observations, and especially for the plates, of which I liave 

 before spoken : they ai-e extremely interesting in the present inquirj'. 

 In accordance with these remarks, I have selected the following 

 stations from ^Ir. Brown's list : — the Orkneys, Belfast, Shields, Cork, 

 Bristol, Plymouth, London, Paris, and Christiania. The reason I 

 have omitted Glasgow and Armagh will be apparent from Mr. 

 Brown's notes. As I have discussed these observations with espe- 

 cial reference to the wave hypothesis, I have most cautiously avoided 

 in my remarks any thing that may at all bear on Mr. Brown's views. 

 The plan I have proceeded on is as follows. I have selected the 



• Report of the Fifteenth Meeting of the British Association for the Ad- 

 vancement of Science, p. 30. 



