BY &. K. SMALLEY, ESQ. 353 



most careful manipulation it will, of course, be understood that 

 I am speaking of terrestrial magnetism. 



This subject was hardly entered upon previous to the year 

 1840, when magnetic expeditions were promoted, and temporary 

 magnetic observatories established in different parts of the world, 

 the objects of such observations being to determine the following 

 elements. The " intensity " of the terrestrial magnetic force the 

 " dip " or inclination of the direction of such force to the horizon 

 and the " declination" or as navigator's call it, the variation, 

 or angle which such direction makes with the astronomical 

 meridian. Meteorological observations were necessarily combined 

 with these, for the two subjects are evidently closely connected. 

 But it must be admitted that we have not made any very great 

 progress in either. 



It is true we are able to conclude that the moon exercises 

 an influence upon terrestrial magnetism, and that it is somehow 

 connected with the solar spots ; we are convinced that it is a 

 function of heat, and that it is connected with electricity, if it be 

 not the origin of those elements. We find that magnetic 

 disturbances are coincident with great thermal changes, but not 

 necessarily with electric storms. Again, most magnetic pheno- 

 mena may be produced by electricity not so the converse, 

 unless we introduce the element motion. It is true we are able to 

 trace something like a general law of the " Diurnal, Annual, and 

 Secular " variations of the magnetic elements, as for example 

 that the declination needle has two maximum deviations from its 

 normal position, in the 24 hours, and likewise in the year. 

 Also, that magnetic storms have their changes which extend 

 over a period of about ten years, which corresponds to the 

 changes which occur in the number and magnitude of the solar 

 spots, and that it is most undoubtedly connected with the 

 " Aurora." 



Still, with all this, how little do we know of the source and 

 laws of a power which may perchance prove to be the key to the 

 universe itself. 



But great improvements have been made in the means and 

 methods of making magnetical observations. The apparatus 

 now employed at the Kew observatory, under the direction of the 



