178 DR. C. CHREE: AN ENQUIRY INTO THE NATURE OF THE RELATIONSHIP 



TABLE XX. Batavia, 1887-98 (Units 1' for Angles, ly for Forces). 



Amplitudes of 24-hour and 12-hour Terms in Fourier Series for Mean Diurnal 



Inequality for the Year. 



32. Disturbances have special attention paid them at Batavia. Following a 

 practice, of which SABINE was an advocate, a reading at Batavia is regarded as 

 disturbed when its difference from the mean reading at that hour during the mouth 

 reaches or exceeds a certain limit. The limiting values adopted at Batavia are 

 l'-3 in D and lly in H and V. 



The arbitrary nature of such criteria, and the difficulty of justifying one limiting 

 value in preference to another, have been more than once pointed out. It is arguable 

 that the limit should vary with the season of the year, and even with the sun-spot 

 frequency. In a European station, for instance, the range of the regular diurnal 

 inequality near sun-spot maximum at midsummer is very large compared to that near 

 sun-spot miniimim at midwinter, and a good deal might be said for a limiting value 

 which bore a fixed ratio to the range from the mean diurnal inequality for the 

 month. 



The disturbed values which exceed the hourly mean, and those which fall below it, 

 are termed respectively "positive" and "negative" disturbances; they are in the 

 first instance treated separately at Batavia, tables being given of the sum of the 

 values of the disturbances and of their number. A final summary gives the aggregates 

 of the positive and negative totals treated* numerically. Table XXI. gives these 

 aggregate values and numbers as published in the annual Batavia ' Observations.' 



The number of disturbances in D is less than half that in V, and little over 

 a quarter that in H. We cannot, however, draw any safe inference as to one element 

 being absolutely more or less disturbed than another. If we calculate the ratios 

 borne by the disturbance limits accepted at Batavia to the mean ranges of the 

 diurnal inequalities for the year in the respective elements, for the period 1887 to 

 1898, we find the following results : 



