318 Royal Society : — 



forms present generally a marked resemblance, tlie hours at different 

 stations exhibit every variety. To exemplify this I have given in a 

 third figure the curve of the westerly disturbance-diurnal variation 

 at St. Helena, of which the form is manifestly tbe same as that of 

 the two curves in fig. 2, whilst the hours of its most marked features 

 exhibit a difference of nearly 1 2 hours of local time from those in 

 fig. 2. 



It may not be unsuitable on the present occasion to take a brief 

 retrospective view of the progress of our knowledge respecting these 

 remarkable phenomena, videlicet, the casual magnetic disturbances, 

 or magnetic storms. Antecedently to the formation of the German 

 Magnetic Association and the publication of its first Annual Report 

 in 1837, our information concerning them went no further than that 

 there occurred at times, apparently not of regular recurrence, extra- 

 ordinary agitations or perturbations of the magnetic needle, which 

 had been noticed in several instances to have taken place contempo- 

 raneously in parts of the European continent distant from each other ; 

 and to have been accompanied by remarkable displays of Aurora, 

 seen either at the locality itself where the needle was disturbed, or 

 observed contemporaneously elsewhere. The opinion which appears 

 to have generally prevailed at this time, was that the Aurora and 

 the magnetic disturbances were kindred phenomena, originating pro- 

 bably in atmospherical derangements, or connected at least in some 

 way with disturbances of the atmospherical equilibrium. They 

 were classed accordingly as " Meteorological Phenomena," and were 

 supposed to have a local, though it might be in some instances a 

 wide, extension and prevalence. 



The special purpose of the German Magnetic Association was to 

 subject the " irregular magnetic disturbances " (as they were then 

 called in contradistinction to the regular periodical and secular varia- 

 tions) to a more close examination, by means of systematized ob- 

 servations made simultaneously in many parts of Germany. With this 

 view, six concerted days in each year were set apart in which the di- 

 rection of the declination-magnet should be observed with great 

 accuracy, by methods then for the first time introduced, at successive 

 intervals of five minutes for twenty-four consecutive hours ; the me- 

 teorological instruments being observed at the same time. The 

 clocks at all the stations were set to Gottingen mean time (Gottingen 

 being the birth-place of the Association), and the observations were 

 thus rendered strictly simultaneous throughout. The high respect 

 entertained for the eminent persons with whom the scheme of the 

 Association originated, obtained for it a very extensive cooperation, 

 not limited to Germany alone, but extending over a great part of the 

 European Continent. The observations of the "Term-days," as 

 they were called, were maintained until 1841, and were all trans- 

 mitted to Gottingen for coordination and comparison. 



The principal results of this great and admirably conducted co- 

 operative undertaking were published in works well known to mag- 

 neticians. They may be summed up as follows : — The phenomena 

 which were the subjects of investigation were shown to be of casual 



