366 



Results of the Makeestoun Obseevations, 1844. 



p. 356, for wMch the seculai- change has been eliminated, we obtain the following quantities, which are the 

 monthly means of the 10 days and 5 days, with the secular change eliminated: — 



Feb. 



10 days, 0-00 

 5 days, 000 



March. April. May. June. July. Aug. Sept. 



Oct. 



Nov. 



Dec. 



2772 2969 2616 2625 2820 3297 3273 2930 2646 2853 2684 3004 

 2811 3033 2742 2720 2925 3200 3251 2958 2739 2910 2862 3065 



The months with the liighest mean values are June and July, December and February ; those with the 

 lowest are March and April, September and November. We have therefore the same law of annual period as 

 from the complete series of observations, namely, maxima near the solstices, and minima near the equinoxes. 

 Au examination of the days whicli liave been selected as most free from disturbances has shewn, that these 

 days are generally near the time of new moon ; at which time, according to the previous discussion, p. 358, 

 the horizontal component has its greatest value, and in accordance with a discussion which follows, p. 369, 

 at which time magnetic disturbances are a minimum. Thougli no elimination of distui-bances will destroy the 

 annual vai-iation of the horizontal component, it is evident, for 1844 at least, that disturbances increase its 

 amount, and it will be a question to be decided by a more extensive induction, whether the annual variation 

 be not due to a regular action of the cause producing the disturbances. 



Effect of Disturb<xnces on the Hourly Means of the Horkontal Component. — The following Taldes contain 

 the diH'erences for each month between the hourly means obtained from the whole hourly observations, and those 

 from the selected series of 10 days and 5 days. 



TABLE XXXII. — Differences between the Hourly Means of Bifilar Scale Readings for the whole Series 

 in each Month, and those for the selected Ten Days ; or Table XXVI. minus Table XXVIII. 



L 



