242 COMMANDER L. W. P. CHETWYND: RESULTS OF MAGNETIC OBSERVATIONS 



8. Comparing the values deduced for the epoch 1st January, 1907, with the 

 corresponding values for 1st January, 1886, or 1st January, 1891 (the epochs of 

 RtiCKER and THORPE'S survey), the resulting mean annual changes at each station are 

 as shown in columns 2, 5, 8, and 11 of Tahle III., in which the stations are arranged 

 according to their latitude. 



9. For comparison, in the same table are given (columns 3, 6, 9, and 12) the mean 

 annual changes at Kew, the differences of mean annual change between Kew and the 

 Field stations being shown in columns 4, 7, 10, and 13. 



10. The resulting comparison shows that the mean annual change of Declination is 

 generally greater at the Field stations than at Kew. The mean change at Kirkwall 

 is l'-5 greater than at Kew, but the results do not indicate a very marked gradual 

 increase with increase of latitude. 



11. The mean .annual change of Horizontal Force appears to be less at the Field 

 stations than at Kew, the differences being greater in the northern latitudes. 



12. The mean annual change of Inclination is less at the Field stations than at 

 Kew, the difference being greater in the northern latitudes. 



13. The mean annual change of Vertical Force during the sixteen-year period 

 1891 to 1907 is less at the Field stations than at Kew, and, with the exceptions of 

 Dublin and Tanera Mor, the Field station results are remarkably similar. 



14. The value of the Declination at Kew for the year 1886, as originally recorded, 

 was 18 18 /- 5, derived from absolute observations only. 



Compared with the value for the year 1 907, derived from quiet-day magnetograms, 

 this gives a mean annual change, during the 21 years' interval, of 5''.3. 



The corresponding values at Greenwich and Stonyhurst are respectively 5''5 and 

 5 /- 6. The mean from the results of those Field stations at which the 21 years' 

 interval is available is 5 / 7, but in the latter case the comparison is from 1886 

 to 1907 . 



15. The originally recorded value at Kew lias, Dr. CHREE informs me, been 

 amended. 



Previous to the year 1890 Kew had no fully corrected declination curves, but in 

 1892 a table of mean annual values was compiled based on the absolute observations 

 corrected for diurnal inequality by means of statistics derived from the diurnal 

 inequalities for short series of years ; these corrections unquestionably improve 

 the value derived from absolute observations alone, and the resulting value for the 

 epoch 1st January, 1886, is 18 15 /- 3; this latter value has been used in calculating 

 the mean change at Kew 1886 to 1907 , resulting in the value 5''2, as given in 

 Table III. 



16. Comparing this value at Kew with corresponding values at those Field stations 

 at which the same 21 years' interval is available, viz., Weymouth, Harwich, Dublin, 

 Milford, Stranraer, and Kirkwall, the mean of the values at these stations is 0''5 

 greater than at Kew. 



