TERRESTRIAL MAGNETISM, ETC. 277 



again to a time of abundant sun-spots which, 

 according to the period hitherto observed, should 

 be about the year 1881 ; and if again there is an 

 abundance of auroras and magnetic storms, there 

 will be further confirmation of the hypothesis of 

 physical connection between the dynamical cause 

 of those grand solar atmospheric storms which 

 produce we may even say which constitute the 

 sun spots and the hitherto mysterious telluric 

 influences concerned in our aerial auroras and un- 

 derground earth currents and surface manifesta- 

 tions of terrestrial magnetism. 



The mariner's compass consists essentially of a 

 magnetized needle, or needles, supported in such 

 a manner as to be free to turn round a vertical 

 axis. The fanciful frontispiece to Lochman's 

 edition of Gilbert's work, contains evidence of the 

 manner of support used when the mariner's com- 

 pass first became known in Europe, as recorded 

 in Guiot de Provence's poem. 



The now ordinary method of support on a 

 bearing-point and cap had probably been used by 

 the Chinese several thousand years earlier, and in 



