356 Mr. Birt on the great Symmetrical 



can be correct which does not fully explain them aspossessed 

 by the acid prepared in its ordinary way. 



I adhere then to the view which I formerly gave, that lam- 

 pic acid consists of formic and acetic acid, with one or more 

 matters not of an acid nature. Of these, aldehyde is the sub- 

 stance which the experiments appear to point out as mixed 

 or associated with the acetic portion of the liquid. This is 

 probable in itself, because the formation of lampic acid is a 

 process of oxidation of the elements of aether, whether in their 

 separate state or in the hydrated condition of alcohol. The 

 first stage of oxidation will produce aldehyde by removing 

 two atoms of hydrogen. The next will convert a portion of 

 aldehyde into acetic acid by adding two atoms of oxygen ; and 

 this acetic acid may, in the act of being formed, possibiy as- 

 sociate itself with an undecomposed portion of aldehyde, if 

 this association is not at a later period, when the union with 

 a base is effected. It is at least certain that all the aldehyde 

 is not oxidated, for free aldehyde is a part of the product. A 

 further stage of oxidation will yield formic acid : — 



C 4 H 5 O ether. 



C 4 H 3 O anhydrous aldehyde. 



C 4 H 3 O 3 anhydrous acetic acid. 



C 2 H O 3 anhydrous formic acid. 

 It would not be difficult to state what appears to me to be 

 the most probable view of the nature of the so-called aldehydic 

 acid itself as obtained from other sources, but I am unwilling 

 to make observations on a substance on which I have not ex- 

 perimented. 



LIV. On the great Symmetrical Barometric Wave of 

 November. By W. R. Birt. 

 [With a Plate.] 

 To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 r r^HE return of the great symmetrical barometric wave last 

 autumn, with its appearance at Dublin in twelve out of 

 seventeen years' observations between 1829 and 1845 inclusive, 

 will render the barometric movements of the ensuing November 

 highly interesting to the meteorologist. Allow me through 

 the medium of your Journal to solicit the attention of ob- 

 servers to this interesting phenomenon, and to point out a few 

 of its essential features by which it may be recognised should 

 it revisit us during the present year. 



The curves of the great symmetrical wave as observed at 

 London in 1842, 1843, and 1844, with the mean of the three 



