276 



DR. CHARLES CHREE: SOME PHENOMENA OF 



4. The number of disturbed days per month varied widely. If we allow equal 

 weight to individual days, we get the means shown in Table II. This table also 

 states the number of days during which the non-cyclic change was plus, zero, or 

 minus. 



TABLE II. Non-cyclic Daily Change from all Disturbed Days. 



The mean value from all disturbed days for I was +0' - 96. 



In the case of D, as already stated, the mean non-cyclic change from the 209 

 disturbed days has the same sign as that from the quiet days ; in the case of H and 

 V the signs for quiet and disturbed days differ. During one average disturbed day 

 H fell as much as it rose 011 four average quiet days, while V rose as much as it fell 

 ou three average quiet days. It will be seen from Table I. that I is the only element 

 in which the monthly means have all the same sign, though in H there is only one 

 exception to the general rule. In all the elements the irregularities in the monthly 

 means seem clear evidence that a much larger number of days would be required to 

 give a reliable indication of seasonal variation. 



5. The monthly mean values already given are all that one requires for the 

 elimination of the non-cyclic effect from the diurnal inequality, if we may assume it 

 to proceed uniformly throughout the 24 hours. This is an assumption which cannot 

 well be avoided in the present state of knowledge, but which, it is well to remember, 

 may not be exact. 



A clearer idea of the significance of the non-cyclic change may, however, be derived 

 from Tables III. and IV. What suggested these tables was the declination 

 phenomenon already described as occurring on a two-day disturbance. Of the 209 

 disturbed days 64 were preceded and followed by days which were not classified as 

 disturbed. The remaining 145 days were made up of 46 sequences of two disturbed 

 days, 9 sequences of three days, 5 sequences of four days, and 1 sequence of six 

 disturbed days. 



Table III. shows the mean non-cyclic changes when groups are formed containing 

 all the days of isolated disturbances, all the " first " days when there was a sequence 

 of disturbed days, and so on. Table IV. gives results for the same groups, only it 

 splits each group into two, according as the non-cyclic change was plus or minus. 

 The fifth and sixth days of the 6-day sequence are omitted, all the other disturbed 

 days are included. 



