376 DR. C. CHREE: ANALYSIS OF RESULTS FROM THE KALMOUTH MAGNETO- 



rate of secular change in D. The annual increase in H at Falmouth from 1891 to 

 1900 was on the average about 10 per cent, larger than at Kew ; but in individual 

 years the two stations show somewhat widely different results. How much of this 

 apparent difference is real it is difficult to say ; part is probably due to instrumental 

 or observational uncertainties. 



The decrease in W at Falmouth from 1891 to 1900 was about 7 per cent, less, the 

 increase in N about 10 per cent, greater than at Kew. 



The total changes from 1891 to 1902 are given by 



SW = -192y, SN = + 390y. 



The force of which these are westerly and northerly components lies in a vertical 

 plane which is inclined to the geographical meridian at an agle of 26'2, and is 

 directed north-easterly. For the period 1891 to 1900 the angle becomes 26'8, or 

 4'l less than the corresponding angle for Kew (see (A), 9). 



Non-cyclic Effect. 



3. As explained in (A), 13, secular change and annual inequality, if they exist, 

 imply a progressive change in the value of an element from midnight to midnight of 

 the average day. There may also be apparent changes due to instrumental causes. 



The contributions to the a-periodic daily variation at Falmouth from secular change 

 and annual inequality are of the same small order of magnitude as the corresponding 

 quantities at Kew ((A), 13). The results of instrumental change are less exactly 

 known than at Kew, but appear to be similarly small. In H the contributions from 

 these causes constitute but a very trifling part of the observed non-cyclic effect on 

 quiet days. In D the contribution from the secular change which tends, however, 

 to reduce the observed effect is not relatively negligible. I have, however, as in (A), 

 made no attempt to separate that part of the non-cyclic effect which is attributable 

 to known causes. 



Tables II. and III. give a complete analysis of the mean observed values of the 

 non-cyclic effect on quiet days in D and H for each month and year of the 12-year 

 period, while Table IV. shows the corresponding mean values in D, W, H, and N for 

 the whole year and the three seasons, winter (November to February), summer (May 

 to August), and equinox. 



When dealing in (A) with the non-cyclic effect in D, I admitted that there was 

 some room to doubt its bond fide character, but indicated several features which 

 pointed to a real physical origin. A comparison of Table II. with Table V. of (A) 

 tends to strengthen the latter view. Whilst the sign of the mean non-cyclic effect 

 fluctuates from month to month, and even from year to year, there is a clear tendency, 

 as at Kew, for + signs to predominate in winter and equinox, whilst in summer the 

 mean non-cyclic effects at the two places are both negative and fairly similar in size. 



