472 



DISCUSSION OF BAKOMETEIC OBSERVATION.S. 



Hence the probable errors of the values in Table IV are the foUowing: 

 maximum, February 4, 0.01G3; minimum, July 23, .0078; mean, .01272. 



It is to be observed that in all the above determinations of probable 

 error, the maximum and minimum values of the error, being derived 

 from Bessel's function, are probably somewhat incorrect by not depart- 

 ing widely enough from the mean value, but the mean value itself is not 

 liable to such an error. 



The probable error of the mean annual pressure, 29.7194, is i 0.00150 j 

 that of the mean of a single year is ± 0.00785. 



BAROMETRIC RANGE. 



Of the readings of the barometer at each of the regular tri-daily obser- 

 vations during a month, corrected for temperature, the highest and lowest 

 values are noted in the register at the end of the month, and the difl'er- 

 ence between them is recorded as the barometric range ior the month. 

 The means of these ranges for like-named months in the twenty-five years 

 are the following: January, 1.255; February, 1.301 ; March, 1.186; April, 

 1.012; May, 0.875; June, 0.727; July, 0.G15; August, 0.655; September, 

 0.846; October, 1.042; I^ovember, 1.221; December, 1.427. 



It will be noticed that the annual fluctuation of baroraetic range 

 copies closely that of the mean departure of the daily mean. The mini- 

 mum in July, the double maximum in December and February, with 

 the intervening value for January, which, though lower than that of 

 either of the adjacent months, is higher than that of any of the remain- 

 ing nine ; all these peculiarities are common to the two functions. They 

 differ, however, in the relative height of the two maxima, the December 

 maximum being in this case higher than that in February. 



SECULAR VARIATIONS OF ATMOSPHERIC PRESSURE AND DISTURBANCE. 



Among the variations of meteorological elements snj)posed to have a 

 period of more than a year, two are embraced within the subject of the 

 present discussion, viz, that of atmospheric pressure, and that of atmos- 

 pheric disturbance, expressed by barometric range. 



Table VI. 



Variation of fhe annual means of pressure. 



