u F T 11 K 11 o R 1 ZO N T A L V RCE 



27 



Table X. — Aggregate usd Mean Amount of the Disti bbances oi the Horizontal Fori i 



Expressed in Scale Divisions. 



MONTH. 



1S40-41. 



July (4089) 



August 4084 



September 3092 



October 3720 



November 2390 



December | 6515 



January 1186 



February j 2664 



March i 3112 



April ' 2138 



May t 2456 



June SOU 



i.-ii-r.' 



1157 



755 



3075 



1284 



1991 



1225 



601 



1822 



1176 



2075 



1211 



794 



1843-M i 



Ml P : 



Amouut. 



ii , force 







1295 



131 



2099 



2399 



915 



o 



44 



39 



676 



1187 



164 



471 

 660 

 169 



34 

 



HI 

 200 

 1412 

 861 

 131 

 





 142 



I 228 

 1412 

 2173 

 2283 

 1402 



sm; 



127 

 1604 



789 

 2390 



56 

 52 

 56 



49 

 54 

 52 

 49 

 50 



49 

 49 

 47 

 44 



1.10 



1.03 



1.11* 



0.97 



1.06 



1.03 



0.97 



0.99 



0.97 



0.97 



93 



0.87* 



0.87 

 1.61 

 1.56 



2.06* 



1.06 



i oo 



0.72 



0.54 



0.66 



0.94 



I 



0.42" 



Mean amount 



53.9 



52.0 



48.6 



46.3 



46.8 



50.6 



1 ,ni 



1.00 



Maxima and minima in the columns of ratios are marked with an asterisk. 



The inequality in the mean amount of the horizontal force disturbances in each 

 year, indicates the year 1843-44 as the minimum year. 



From the preceding results. Ave may assume the month of November, 1843, as 

 the epoch for the minimum of the cloven (ten'?) year inequality, as far as indicated 

 by the differential observations of the horizontal force. 



Further Analysis of the Disturbances of the Horizontal Force. — The distribution 

 of the disturbances in number and mean amount over the several months of the 

 year has been given in Tables IX. and X. From Table IX. we learn that the 

 disturbances are greatest in number in September and March or April, or about the 

 time of the equinoxes, and least in number about January and June, or about the 

 time of the solstices. At the autumnal equinox the numbers exceed those of the 

 vernal equinox ; the same law was found at Toronto ; also the numbers are smaller 

 at the summer solstice than at the winter solstice, in perfect accordance with the 

 result found at Toronto. These results are shown graphically on the annexed dia- 

 gram, which contains also the ratio of the disturbances for the declination in which 

 the same law is apparent. 



(B). — Distribution of the Number of Disturbances ih the several Months of the Year. 

 Full line for horizontal force. Dotted line for declination. 



- l, rt Crt — ., 3 *, o o a; !2 



