of Terrestrial Magnetism. 99 



British system of observation to the modes in which the investi- 

 gations that had been thns commenced could be most success- 

 fully prosecuted, the Report of the Royal Society manifested 

 a sagacity which subsequent experience has so fully confirmed 

 that we may, with propriety, on the present occasion recall one 

 or two sentences of that Report, because they strike the key-note 

 of all the discoveries which have since been made, and also because 

 to this day they appear to be too little understood, or at least too 

 little regarded, by many who profess to take part in a system of 

 observation which has accomplished so much for this branch of 

 science. The extracts will be very brief. 



" All the magnetic elements are at each point now ascertained 

 to be in a constant state of fluctuation, and affected by transient 

 and irregular changes ; and the investigation of the laws, extent, 

 and mutual relations of those changes is now become essential 

 to the successful prosecution of magnetic discovery, for the fol- 

 lowing reasons : — 



" 1st. That the progressive and periodical changes are so 

 mixed up with the transitory changes that it is impossible to 

 separate them so as to obtain a correct knowledge and analysis 

 of the progressive and periodical, without taking express account 

 of and eliminating the transient and irregular ; . . . . and further, 

 because the theory of these transitory changes is in itself one of 

 the most interesting and important points to which the attention 

 of magnetic observers can be turned, as they are no doubt inti- 

 mately connected with the general causes of terrestrial mag- 

 netism, and will probably lead us to a more perfect knowledge 

 of those causes than we now possess." 



The interest with which these fluctuations were regarded at 

 the close of the German Association, as shown by the preceding- 

 extracts, was much increased by the results of the first year of 

 the observations made, on days concerted with European obser- 

 vatories, at the British Colonial stations in Canada, St. Helena, 

 the Cape of Good Hope, and Van Diemen Island. By the inter- 

 comparison of these it was found that the disturbances were con- 

 temporaneous, not only over a limited area in Europe, as pre- 

 viously known, but also at all these widely distributed stations 

 situated in parts of the globe most distant from each other. 

 They were obviously affections common to the whole surface of 

 the earth ; and thus the improbability of their having a local or 

 atmospheric origin was strengthened and confirmed. Whilst, 

 however, evidence was conclusive in regard to their general con- 

 temporaneous occurrence, and whilst fluctuations of the most 

 marked character were noticed to be strictly synchronous in the 

 northern and southern hemispheres as well as in Europe and 

 America, it was also found that at stations remote from each 



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