of Magnetic Ehtntnts* 



41 



Greenwich Magnetic Diurna 



1 Inequalities 



, 1881 



). 



Element. 



Range. 



Sums of 24 Deviations. 



All 

 days. 



Quiet Excess 

 days, all days. 



All 

 days. 



3()'-83 



Quiet 

 days. 



32'58 



Excess 

 all clays. 



+4' 25 



Declination, in minutes ... 



6'04 



6'12 



-0'-08 





320 

 221 

 156 



324 - 4 



1952 

 1240 



j 774 



1727 



1277 



673 



+225 



-.37 

 + 101 



Horizontal Force, metric. . . 

 Vertical Force, metric 



240 



137 



1 



-19 

 + 19 



Thus, comparing Greenwich values only, we find for 1889 

 mean of the three values of excess under Range =—1, and 

 the mean under Sums of Deviations =+i)6. The latter is 

 probably a better indication than the simple range of the 

 influence of magnetic irregularities on the diurnal inequality 

 formed from all days. But the discussion of the records of 

 other years will throw further light on this point. 



The question whether, in forming diurnal inequalities, all 

 days should be employed, or selected days only, is one that has 

 forced itself into notice in the discussion also of meteoro- 

 logical elements. For instance, in air-temperature, the 

 ordinary diurnal change is in winter, at times, quite reversed, 

 and the barometric movements are sometimes large and very 

 irregular. But yet all days have been usually included in 

 determining diurnal inequality. It may be questionable 

 whether it is proper arbitrarily to reject days because they 

 appear to be affected with irregularities which may themselves 

 have a diurnal period. Indeed, considerable variation in am- 

 plitude of motion may be found to exist in magnetic registers 

 on different quiet days in the same month. Considering, 

 however, the amount of work involved in the tabulation of all 

 days, the proposal to discuss the records of British magnetic 

 observatories for five selected days monthly, in each year, will 

 make a practical beginning in that which in magnetism is so 

 much required — the tabulation of the records of different 

 observatories on one uniform plan, in order to effect a more 

 efficient and trustworthy comparison of results. 



