92 SCIENCE PROGRESS. 



It may be remarked in passing that a remarkable 

 alteration in the amount of the secular change has been 

 noticed in the Declination and Inclination at the following 

 observatories : Bombay, Batavia, and Hong Kong about 

 the period of the eruption of Krakatoa in 1883. This may 

 be only a coincidence, but may it not also point to the 

 possibility that the changes below the surface of the earth 

 which culminated in that mighty explosion, and may still 

 be at work, have had, and continue to have, magnetic 

 effects which are recorded by the needles at those observa- 

 tories ? 



Critical investigations have for many years been directed 

 to the elucidation of the causes of the observed diurnal 

 variations of terrestrial magnetism. This work was long 

 seriously retarded by the various methods adopted at different 

 observatories for recording their results, obliging those who 

 entered upon a comparison of such results to go through a 

 tedious conversion of them into a common method. It may 

 be said that the first large departure from this objectionable 

 practice occurred when the International Polar Inquiry of 

 1882-83 was undertaken by the various expeditions. 



This was an important step in the right direction, but 

 there remains much to be done, as shown by the ten re- 

 ports of the British Association Committee on "the best 

 means of comparing and reducing magnetic observations ". 

 Their last report consists of an able and suggestive paper 

 by Dr. Chree, being the analysis of the results of five years' 

 observations on "quiet days" at Kew, and is well worthy 

 of attention as indicative of the present state of our know- 

 ledge as regards the diurnal variation of the three magnetic 

 elements. 



Such investigations only encourage one in the hope that 

 the much required observations in southern latitudes may 

 be undertaken. The observatories at the Cape and Mel- 

 bourne could do invaluable work if it were carried out on 

 the lines of Kew, for example. 



Lastly, what more is there to be said about magnetic 

 observations and their bearings ? We do not know why 

 the earth is a magnet, the cause of the secular change of its 



