;^^o 



Results of Makeestoun Observations, 1844. 



TABLE XLV. — Hourly Means of the Balance Magnetometer Micrometer Readings for the Five Days 



least disturbed in each Month of 1844. 



Tliese Tables give very remarkable results, the means for the 10 days and for the 5 days selected agree 

 verv nearlv with each other, but they differ vci-y considerably in some cases from the means of the whole ob- 

 servations. Considering at first the mean of the 60 days representing the mean for the year, free or nearly free 

 from intermittent disturbances, we find that the diurnal variation consists of two nearly equal maxima and two 

 nearlv equal minima ; the principal of the former occurs at 4'' 10™ p.m. and the other at 8'' 10™ .v.m., while 

 the principal minimum occurs at noon and the secondary minimum at l"" 10™ a.m. The mean for the 120 days 

 differs from that for the 60 days, only in placing the principal ma.ximum an hour later, namely, at 5'' 10™ p.m. 

 The effect of the intermittent disturbances tlierefore is nearly to efface what is really the principal minimum 

 and to exaggerate what is only a secondary muiimum ; the range of the mean diurnal variation when freed 

 from the eftijct of disturbances is little more than a fourth of that obtained from the whole series of observations. 

 When the non-disturbed variations for the different months arc examined, it is at once apparent that the matters 

 which have been noted as remarkable in the total results are chiefly or altogether due to distiu-bances ; in fact, 

 the diurnal variation consists in the eight months from March till October of two maxima and two minima, and 

 resembles generally the result for the year, the earlier maximum being at times the principal. The variation in 

 the four winter months differs somewhat from that for the other months, being more like a single variation ; 

 there are, however, some differences which may be accidental, but which will be considered in connection with 

 the observations for ia45. The following Table contains the approximate epochs of the singular points for each 

 month, the principal are indicated by -|- and — 



