372 Results of Makerstoun Observations, 1844. 



maximum about 6 h a.m., but it is not well marked. The sums of negative disturbances are a minimum about 

 3 h 10 m p.m., and a maximum about midnight ; they are a secondary minimum at 6 h 10 m a.m., and a maximum 

 at 10 h 10 m a.m. On the whole, therefore, the epochs of maximum for the positive di sturbancearewithin 

 an hour of those of minimum for the negative disturbance, and vice versa. 



Diurnal Variation of the Mean Disturbance. — The following are the mean disturbances, in scale divisions 

 for each hour, without regard to sign : — 



12b xh a.m. 2h 3 h 41' 5'i 6h 7>> 8»' 9 h 10b llh Ob 1>> P.M. 2 h 3b 4h 5>> 6h 7 1 ' 8'' 9 h 10b ll h 

 4-26 4-05 4-41 3-82 3-55 4-43 3-78 383 4-24 435 4-44 4-30 4-46 3-93 4-00 4-66 4-79 4-72 4-39 4-32 4-21 4-49 418 4-35 



These quantities give nearly the same law of variation as the mean differences ; the maximum disturbance 

 of the horizontal component occurs at 4 h 10 m p.m., the minimum about 5 h a.m. ; a secondary maximum occurs 

 about 10 h a.m., and a minimum about l h p.m. 



Annual Variation of the number of Positive Disturbances. — The following are the numbers per cent, of 

 hourly observations hi each month, which were positive or greater than the normal means at the corresponding 

 hours : — 



Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



54-0 



57-7 



66-0 



52-1 



52-6 



45-0 



46-6 



52-8 



55-2 



60-6 



56-9 



61-1 



The greatest number of positive disturbances occurs near the equinoxes, and the least number at the 

 summer solstice ; on the whole, the number for the sun south of the equator is greater than for the sun north 

 of the equator, the number per cent, for the former being 58 - 4, and for the latter 50 - 7- In the year 1844, 

 there were, in 100 observations, 54-5 greater and 45'5 less than the normal means at the corresponding 

 hours. 



Diurnal Variation of the numbers of Positive Disturbances. — The numbers per cent, of hourly observations 

 which were greater than the monthly means at the corresponding hours, are as follow : — 



12M h A.M. 2 h 3 h 4 h 5 h 6 1 ' 7 h 8 1 ' 9 1 ' 10 b ll 1 ' h l h P.M. 2 1 ' 3 1 ' 4 1 ' 5 h 6 h 7 h 8 1 ' 9 h 10 h ll 1 ' 



47-5 47-8 44-9 50-3 51-6 580 55-4 55-1 55-4 53-5 54-1 59-2 605 57-6 63-4 59-9 67-2 64-0 58-9 57-3 538 46-5 52-5 46-S 



The number of positive disturbances is a maximum at 4 h p.m., and a minimum about 2 h a.m.; there is 

 the appearance of a secondary maximum at 5 h a.m., and minimum at 9 h 30 m a.m. From about 9 h p.m. till 

 2 h a.m., the number of positive disturbances is less than the number of negative disturbances ; at all the other 

 hours of the day the number of positive disturbances is greatest. There are nearly two positive disturbances 

 for one negative disturbance at 4 h p.m. 



Diurnal Variation of the Positive and Negative means of Disturbance. — A comparison of the diurnal laws 

 of variation for the sums and numbers of positive disturbances, will shew that they give nearly the same epochs 

 of maxima and minima ; it is uncertain, therefore, whether the variation of the sums depends solely or chiefly 

 on the variation of the numbers of disturbances which are positive or negative. The following are the mean 

 values, in scale divisions, of the positive and negative disturbances for each hour, obtained by dividing the 

 sums of the positive disturbances by their number, and the sums of the negative disturbances by their number : — 



12''l h A.M. 2 h 3 h 4 1 ' 5 h 6> ; 7 h 8 1 ' 9 1 ' 10 h ll 1 ' 12 h l 1 ' P.M. 2 1 ' 3 h 4 h 5 h 6 h 7 b 8 h 9 h 10b ll 1 ' 



+ 3-32 2-83 2'94 2-85 2'98 3-63 382 339 3-65 3-72 3-64 396 462 4-19 4-16 5-05 5-17 5-00 4-55 4-03 4-05 3-35 3-05 2 91 

 -5-11 5-16 5-34 4-80 4-17 552 372 438 4-96 508 5-39 478 4-20 3 58 371 4-06 4-02 4-23 4-17 4-72 4-38 5-48 5-42 5-60 



These values differ considerably ; the law of their variation is almost exactly that already obtained for 

 the sums of positive and negative disturbance. 



The maximum of the mean positive disturbance occurs about 4 h 10 m p.m. 



The minimum „ 2 h 10™ a.m. 



There is also the appearance of a secondary maximum about 6 h a.m. 



The maximum of the mean negative disturbance occurs about l h 30 m p.m. 



The minimum ll h m p.m. 



There is also a secondary maximum about 6 h a.m., and minimum about 10 h a.m. 



The numbers of positive and negative disturbances seem, on the whole, to obey the same law as their 

 respective sums. 



