474 Royal Society : — 



tingent upon the direction of the magnetic meridian at each place, 

 and producing extreme deflections to the East and to the West twice 

 in the twenty-four hours, the turning hours being about six hours 

 apart, and stated to be appropriately represented by a formula of two 

 terms, one involving the sine of the hour-angle, and the other the 

 sine of twice that angle : the phenomena of the double progression 

 at Toronto and Hobarton are thus viewed by him as " Types of all 

 that happens beyond the limits of the torrid zone." 



If I have represented M. Secchi's views correctly, and I think I 

 have done so, the question between the conformity to nature of his 

 views and mine would be tested by the facts (when they should be 

 known) of the diurnal variation at a station in the middle latitudes 

 where the principal influence of the magnetic storms should take 

 place, not in the hours of the night, but in those of the day. 

 According to my interpretation of the phenomena at Toronto and 

 Hobarton, such a station ought to exhibit a single progression ; ac- 

 cording to M. Secchi's, a double progression with turning hours 

 about six hours apart. Such a station would therefore furnish what 

 might be deemed a crucial experiment. In the extension of our ex- 

 perimental knowledge which might be expected to follow from the 

 adoption by Her Majesty's Government of the recommendations of 

 the Royal Society and of the British Association, which have been 

 communicated to Lord Palmerston with so much earnestness of pur- 

 pose, and with so just an appreciation of their importance, by His 

 Royal Highness the Prince Consort, as President of the British As- 

 sociation, it had been anticipated that it would not be long before 

 the evidence derivable from such a station would be secured to us. 

 I have found it, however, sooner than I had expected, or had hoped 

 for, in the three years and ten months of hourly observations of the 

 Declination at Pekin, from January 1, 1852, to October 31, 1855, 

 made under the superintendence of M. Scatchkoff, attached to the 

 Russian Embassy at Pekin, and published by our distinguished 

 foreign member, M. Kupffer, in the volumes of the 'Annales de 

 l'Observatoire Physique Central de Russie.' The results of these 

 observations, as far as they bear on the questions of the general phe- 

 nomena of the diurnal variation, and on the mode in which these 

 may be explained, form the subject of the present communication. 



The examination of these observations was first undertaken by me 

 for the purpose of ascertaining, as far as possible by their means, the 

 precise epoch of minimum in the so-called decennial period of the 

 magnetic storms. "With this view a separation was made of the 

 larger disturbances in the usual manner, and their laws at Pekin in- 

 vestigated. In this process it was soon perceived that the hours of 

 principal disturbance were those of the day, both in the easterly and 

 in the westerly disturbance deflections ; and on subsequently receiving 

 from the computers the annual mean of the diurnal variation cor- 

 responding to the whole period of observation (in which the omission 

 of disturbed observations during the hours of the night had been com - 

 paratively very inconsiderable), I was not surprised to find that it exhi- 

 bited no trace of a double progression. The results were as follows : — 



