1863.] Mr. Airy — Analysis of 177 Magnetic Storms, 49 



Aggregate or Mean for each year, and the Aggregate for the seventeen years. 

 The Aggregate for the Northerly Force is negative in every year. That for 

 the Westerly Force is on the whole negative ; the combination of the two 

 indicates that the mean force is directed about 10° to the east of south. 

 That for the Nadir Force appears negative, but its existence is not certain. 



Some peculiarities of the numbers of waves with different signs are then 

 pointed out. For "Westerly Force and also for Nadir Force, the numbers 

 of + waves and — waves are not very unequal ; but for Northerly Force 

 there are 177+waves and 277— waves. In Nadir Force it is almost an 

 even chance whether a storm begins with a +wave or with a — wave ; and 

 the same with regard to its ending ; in Westerly Force the chances at 

 beginning and ending are somewhat in favour of a + wave ; but in Northerly 

 Force two storms out of three begin with a — wave, and ten storms out of 

 eleven end with a —wave. 



The beginnings and ends of the storms are also arranged by numeration 

 of the combination of waves of different character in the different elements 

 (as, for instance, Westerly Force + with Northerly Force — , Northerly 

 force + with Nadir Force +, &c.) ; but no certain result appears to 

 follow, except what might be expected from the special preponderances 

 mentioned above, leaving the relative numbers of the combinations a 

 matter of chance in other respects. 



Tables IV., V., VI. exhibit the Absolute Aggregates of Fluctuations and 

 Absolute Means of Disturbances without regard to sign. In interpreting 

 these it is remarked that the large — mean force in the northerly direction 

 necessarily increases the Aggregate and diminishes the Number of Waves. 

 With probable fair allowance for this, it appears that the Numbers of Waves 

 are sensibly equal, that the Sums of Fluctuations are sensibly equal, and 

 that the Means of Disturbances are sensibly equal for Westerly Force and for 

 Northerly Force. But the Number of Waves for Nadir Force is less than 

 half that for the other forces ; while the Sum of Fluctuations is almost three 

 times as great as that for the others, and the Mean of Disturbances almost 

 three times as great. 



Attempts are made to compare the epochs of the waves in the different 

 directions, but no certain result is obtained. 



Tables VII., VIII., IX. exhibit for each storm, and for each year, and 

 for the whole period the Number of Irregularities, the Absolute Sum of 

 Irregularities, and the Mean Irregularity. It appears that the value of Mean 

 Irregularity is almost exactly the same in the three directions, that the 

 number of irregularities is almost exactly the same in Westerly Force and in 

 Northerly Force, but that the number in Nadir Force is almost exactly 

 half of the others. 



It is certain that the times of Irregularities in the Westerly and Northerly 

 directions do not coincide. There appears some reason to think that Nadir 

 Irregularities frequently occur between Westerly Irregularities. 



In Table X. the Aggregates of Fluctuations and Irregularities are arranged 



