lleport on Terrestrial Magnetism. 



before the Royal Society, in a memoir which has been commu- 

 nicated by him, renders it unnecessary here to enter into the 

 explanation given of them by M. de Humboldt. He has re- 

 ferred to them in order that those members of the Royal Society 

 who have most advanced the study of terrestrial magnetism, and 

 who are acquainted with the localities of colonial establishments, 

 may take into consideration, whether, in the new stations to be 

 established, a bar of great weight furnished with a mirror should 

 be employed, or whether Gambey's needle should be used : his 

 wish is only to see the lines of magnetic stations extended, by 

 whatever means the precision of the observations may be at- 

 tained. 



M. de Humboldt concludes by begging His Royal Highness 

 to excuse the extent of his communication. He considered it 

 would be advantageous to unite under a single point of view 

 what has been done or prepared in different countries towards 

 attaining the object of great simultaneous operations for the dis- 

 covery of the Jaws of terrestrial magnetism. 



Having very fully laid before the Council the contents of M. 

 de Humboldfs letter, we have now to offer our opinion upon 

 the subject it embraces. There can, we consider, be no ques- 

 tion of the importance of the plan of observation which is here 

 proposed for the investigation of the phenomena of terrestrial 

 magnetism, or of the prospect which such a plan holds out of 

 the ultimate discovery of the laws by which those phenomena 

 are governed. Although the most striking of these phenomena 

 have now been known for two centuries, although careful obser- 

 vations of them have within that period been made, and that still 

 more care and attention have been bestowed upon those more 

 recently discovered, yet the accessions to our knowledge, not 

 only regarding the cause of the phenomena, but even with re- 

 spect to the laws which connect them, bears a very small propor- 

 tion to the mass of observations which have been made. This 

 has arisen in a great measure, if not wholly, from the imperfec- 

 tion of the data from which attempts have been made to draw 

 conclusions. Whatever theories may have been advanced in ex- 

 planation of these phenomena, or attempts made to connect them 

 by empirical laws; still, whenever comparisons have been insti- 

 tuted between the results of observation and such theories or 



