THE MOST RECENT VALUES OF THE MAG- 

 NETIC ELEMENTS AT THE PRINCIPAL 

 MAGNETIC OBSERVATORIES OF THE 

 WORLD. 



[Through the courtesy of the Kew Committee of the Royal Society 

 and of Mr. Chree, the Superintendent of the Kew Observatory, arrange- 

 ments have been made for the publication, in this journal, of a table show- 

 ing the mean annual values of the magnetic elements as determined at the 

 various magnetic observatories of the world. It is intended that this table 

 shall appear about July in each year. — Ed.] 



7"* HE phenomena of terrestrial magnetism possess so 

 many points of interest that in a short article it is 

 only possible to glance at a portion of the field. The mag- 

 netic phenomena at any one place show, as is well known, 

 a continual fluctuation. There is a general drift, or secular 

 variation, proceeding in the same direction for many years, 

 together with more or less regular annual and diurnal 

 variations and probably other minor oscillations of a cyclic 

 character. There are also numerous irregularities, which 

 when sufficiently intense are dignified with the title of mag- 

 netic storms. 



To analyse the phenomena it is necessary to consider 

 separately the various magnetic elements. Three elements, 

 two being angles measuring direction and one a measure of 

 intensity, suffice to define the magnetic force. It is custom- 

 ary and more convenient, however, to record the inten- 

 sity not of the whole force but of its horizontal and vertical 

 components. The usual angular elements are the declina- 

 tion, or angle the horizontally suspended magnetic needle 

 makes with the geographical meridian, and the inclination, 

 or dip, which is the angle made with the horizontal plane 

 by a magnetic needle freely movable in the magnetic 

 meridian. 1 



One of the fundamental objects of magnetic observations 

 is to supply the data required for the construction of maps, or 



1 The magnetic meridian is the vertical plane which contains a freely 

 suspended horizontal magnet. 



