consequence, in some way or other, of the sun's action, could not 

 be doubted, from the fact that the period in which the variation 

 takes place is a solar day ; and whilst the progression was regarded 

 as a single one in the twenty-four hours, it accorded sufficiently well 

 with the prevailing notion, that the magnetic variations were pro- 

 duced by variations of temperature, to meet the general view, not- 

 withstanding the grave doubts and dissents which from time to 

 time had been expressed by those who more closely examined the 

 phenomena of particular localities. As the existence of a well- 

 marked double progression at some stations on the globe could, 

 however, no longer be disputed, the difficulty which now presented 

 itself was to explain in what way this apparently double action of 

 the sun was produced. 



On a careful examination of the diurnal motion of the declination 

 magnet on different days of the years referred to at the commence- 

 ment of this paper, it soon became obvious that, both at Hobarton 

 and Toronto, many days occurred in which the diurnal march was a 

 single progression, the nocturnal retrogression wholly disappearing ; 

 and that there were many more days in which this was more or less 

 approximately the case. It further appeared, on subsequently com- 

 paring the observations of the same years at both stations, that the 

 days most distinguished by a large arid even sometimes an extrava- 

 gant interruption of the otherwise continuous single progression, 

 were generally the same days at both stations ; and by extending 

 the comparison to other though less complete series of observations 

 in other parts of the globe, these days were identified as those on 

 which magnetic storms had prevailed; viz. days which had been 

 distinguished by the occurrence of perturbations, often of very con- 

 siderable magnitude, affecting simultaneously the magnetic elements 

 in all parts of the globe as far as observation extended, presenting a 

 remarkable uniformity in the effects produced at contiguous stations, 

 but (as shown by the simultaneous observations at Toronto and 

 Hobarton) manifesting a great variety both in the character and the 

 amount of disturbance in parts of the globe distant from each 

 other. To separate the observations affected by these exceptional 

 and casual influences from the ordinary and what might be deemed 



that this should be the case, since the observations at Greenwich and Kew have 

 shown that the progression is douhle at those stations. 



