Location of the Isogonic Lines. 



practical men, (navigators, geographers, merchants, courtiers and poli- 

 ticians) in the variation of the magnetic needle, and led to the con- 

 struction of a variety of instruments for facilitating the necessary 

 astronomical and magnetic observations. Solar compasses are spoken 

 of among the instruments then devised, and we hear for the first time 

 of "variation charts," for Columbus had also found that on either 

 side of his line of no variation there were easterly and westerly decli- 

 nations, increasing as this line was departed from. As the interest 

 increased and the investigation of the phenomena was extended, 

 another great line of no variation was discovered in the eastern hemis- 

 phere; the dip or vertical inclination of the magnetic needle was 

 observed by Norman, and the great work of Gilbert, De Magnete Nova, 

 replete with information and valuable suggestions and inferences, gave 

 stimulus to the study of this branch of physics. 



Then the Astronomer Halley, after scientific voyages around the 

 world under the auspices of the British government, brought together 



discussions of tin- data obtained enabled him to indicate, with remark- 

 able closeness, the location of the magnetic poles of the earth, proving 

 them to be far distant from the geographical points. Improvements 

 in instruments, methods and the manner of observation rapidly fol- 

 lowed, and hundreds of names — memorable in science — are now met 

 with, while the invention of apparatus keeping pace with discovery, 

 the hitherto small but important variations came to be studied as well 

 as the intensity of the magnetic force, and its increase and decrease. 

 Then came the establishment of magnetic and meteorological observ- 

 atories, and we are to-day reaping the profits of thousands of original 

 investigations m the varied magneto-electric devices of utility and 

 convenience, which the study of this branch of physics has so greatly 

 furthered. 



Our time will not admit of even a brief account of the great mag- 

 netic observatories of the world, or of the toilsome journeys into dis- 

 tant lands made by scientific men, in order to discover the cause and 

 extent of these variations in the earth's magnetic force. The names 

 of Gay Lussac, Humboldt, Bache, Parry, Boss, Hansteen, Oersted, 

 Scoresby, Sabine, Erickson, Arago, Gauss, Faraday, Airy, Lefroy and 

 Thompson remind the student of a thousand magnificent discoveries, 

 which cast a lustre upon each name, as bright as the dazzling rays ot 

 the electric arc itself. Thus the magnetic observatories of Europe* 



