418 



The author obtains formulae by which the ratio of the circum- 

 ference of a circle to its diameter may be computed with much 

 greater facility and expedition than by any of the ordinary methods. 



A paper was also in part read, entitled, " Inquiries respecting the 

 Constitution of Salts, of Oxalates, Nitrates, Phosphates, Sulphates, 

 and Chlorides." By Thomas Graham, Esq., F.R.S.Ed., Professor of 

 Chemistry in the Andersonian University of Glasgow, &c. &c. Com- 

 municated by Richard Phillips, Esq., F.R.S. 



Report upon a Letter addressed by.M. le Baron de Humboldt 

 to His Royal Highness the President of the Royal Society, 

 and communicated by His Royal Highness to the Council. 



To His Royal Highness the President and Council of the 

 Royal Society. 



Previously to offering any opinion on the important communica- 

 tion on which we have been called upon to report, we feel that it 

 will be proper to lay before the Council a full account of the com- 

 munication itself. In this letter M. de Humboldt developes a plan 

 for the observation of the Phenomena of Terrestrial Magnetism 

 worthy of the great and philosophic mind whence it has emanated, 

 and one from which may be anticipated the establishment of the 

 theory of these phenomena. 



After his return from the equinoctial regions of America, M. de 

 Humboldt, in the years 1806 and 1807, entered upon a careful and 

 minute examination of the course of the diurnal variation of the 

 needle. He was struck, he informs us, in verifying the ordinary re- 

 gularity of the nocturnal period, with the frequency of perturbations, 

 and, above all, of those oscillations, exceeding the divisions of his 

 scale, which were repeated frequently at the same hours before sun- 

 rise. These eccentricities of the needle, of which a certain periodicity 

 has been confirmed by M. Kupffer, appeared to M. de Humboldt 

 to be the effect of a reaction from the interior towards the surface 

 of the globe — he ventures to say, of " magnetic storms" — which in- 

 dicated a rapid change of tension. From that time he was anxious 

 to establish to the east and to the west of the meridian of Berlin, 

 apparatus similar to his own, in order to obtain corresponding ob- 

 servations made at great distances at the same hours, but was for a 

 long period prevented putting his plan into execution by the dis- 

 turbed state of Germany and his departure for France. 



The Baron de Humboldt and MM. Arago and Kupffer having, 

 by the cooperation of many zealous observers, succeeded in esta- 

 blishing permanent magnetic stations extending from Paris to China, 

 M. de Humboldt solicits, through His Royal Highness the President, 

 the powerful influence of the Royal Society in extending the plan, 

 by the establishment of new stations. The plan which he proposes, 

 and which has been successfully carried into execution over a large 

 portion of the north-eastern continent, is that magnetical observa- 

 tions, whether of the direction of the horizontal and inclined needles, 

 or for the determination of the variations of the magnetic force, 



