42 Mr. W. R. Bin oJi the Great Symmetrical 



mean value for each station, then a chart representing to the 

 eve the line of greatest symmetry with the lines of deviation 

 on each side, could readily be constructed. The following table 

 is intended to illustrate these remarks. The values of the most 

 prominent points of the wave are given, from which the de- 

 parture from symmetry may easily be deduced. The same 

 may be done for other stations. 



Barometric readings of the most prominent points of the Great 

 Symmetrical Wave of November ISl?. 



My attention has been called by Mr. Chalmers of Weston- 

 super-Mare, Somersetshire, — to whom 1 am indebted for the 

 readings in the fourth column of the foregoing table, — to the 

 similarity existing between the great wave of 1798 and ISi? 

 at London. The observations in 179S were made by Luke 

 Howard, Esq. A chart of the barometric movements during 

 the entire year, illustrates an article on the influence of the sun 

 and moon on the barometer, published in tiie Philosophical 

 Magazine for 1800. In this chart the movements during No- 

 vember are seen to be greatly in accordance with tlie ti/pe as 

 expressed above. Fig. 3 in the engraving, illustrating this 

 article, is the projection of these movements on a similar scale 

 to the curves of 1846 and IS-t?, The similarity between the 

 curves of 1847 and 1798 is very considerable. The vertical 

 lines passing through the principal points of these curves 

 clearly indicate that the epochs of these points in 1798 and 

 1847, especially the two interior minima and the two exterior 

 maxima, diffired from, each other but an hour or tvco: in this 

 respect the resemblance is very close. The horizontal lines 

 are intended to show the deviation from symmetry, supposing 

 the two interior minima, being at the same altitude, to repre- 

 sent perlect symmetry. [The equal altitudes of the two exterior 

 maxima is a much better general expression of this element.] 

 The highest horizontal line in fig. 1, just touching the second 

 interior minimum, indicates a reading of 30"2y9 ; the lowest 



* These numbers have been tak'.-n from a curve with which I have been 

 furnished hy John Voiid, Esq. ot Halifax. Tlio.se at London and We.ston 

 are given as read ofl' from the scale. 



