XXIV GENERAL RESULTS OF THE MAKERSTOUN OBSERVATIONS. 
38. Diurnal Variation of the Effect of Disturbance on the Mean Declination—When we deduce the 
yearly mean declination from the days selected as free from intermittent disturbance (No. 35.) we obtain the 
following results :— 
Mean Declination from all the hourly observations in 1844, = 25° 17"06, 1845, = 25° 1132 
Soo ters so nets from the hourly observations in the selected 120 days of 1844, = 25° 17°08 
1845, = 25° 11°39 
The effect of disturbances, therefore, on the yearly mean position may be considered zero. When we compare 
the monthly means, as deduced from the 10 days selected in each month of 1844 and the 7 days selected in 
each month of 1845, with those deduced from all the hourly observations, we find that the average difference 
(independent of sign) for the monthly means in these two years is about 02; a difference which may be referred 
with more probability to the effects of regular laws, or the fewness of the observations, than to the effect of 
intermittent disturbance, which is zero on the yearly mean. It is evident, therefore, that, for the purpose of 
the present discussion, we may assume, with little probable error, that the monthly mean from both series has 
the same value (as in Tables 13 and 14), and take the differences of the hourly means in the two series as 
measures of the effect of disturbance; any possible error in this assumption can affect the values of the dif- 
ferences but slightly ; the epochs of the maximum and minimum would still remain unaltered. In this man- 
ner the following Table has been formed :— 
TABLE 15.—Differences of Disturbed and Undisturbed Diurnal Variations of Westerly Declination, 
as deduced from Tables 13 and 14, exhibiting the effect of Irregular Disturbance on the Hourly 
Mean Positions. 
39. The conclusions from this Table are,— 
lst, That the greatest effect of disturbance in increasing the westerly declination occurs 
In Dec. Jan. Feb. March, April. May, June. July, Aug. Sept. Oct. Noy. 
About 1» 40™ p.m. 95 a.m. to 1" PM. 1 40™ p.m. 8» a.m. 8) a.m. 
