ON MAGNETICAL AND METEOROLOGICAL OBSERVATIONS. 7 



masked by the growing influence of other shocks whose point of action is 

 nearer, is now one of the principal points to which attention must be directed. 

 The great mass of the magnetic bars used for the regular determinations, and 

 for observations of small and moderate disturbances, throws some obstacles 

 in the way of this inquiry, when the changes of magnetic force are very sud- 

 den and irregular, which seems more likely to be prosecuted effectually by 

 the use of very small bars capable of being instantly affected by short and 

 sudden shocks. But however this may be, the occurrence of many and re- 

 markable storms during the continuance of these observations, at the most di- 

 stant localities, and with all their detail of circumstances, has given a very 

 high degree of immediate interest to this branch of the inquiry, and occa- 

 sioned a change in the contemplated order of publication of the reports. It 

 has been considered advisable to collect together from all the returns the cases 

 of remarkable disturbances observed, arrange them in chronological order, 

 and publish them in volumes by themselves. Those of 1840 and 1841 will 

 appear in the course of the summer. By pursuing this course it alone be- 

 comes practicable to mature such a plan of extra or storm observation (whe- 

 ther by the use of smaller needles or by other processes which will suggest 

 themselves,) as can be fairly tried and effectually brought into action while 

 the colonial observatories still subsist. Among those which will be included 

 in this first publication, the great disturbance which took place on and about 

 the 25th of September, 1841, though not the greatest in point of actual devi- 

 ation which has occurred, is yet in many respects one of the most remarkable. 

 It was observed at Greenwich and immediately made the subject of a circular 

 communication addressed by the Astronomer Royal to his brother observers. 

 Speedily accounts" dropped in of the observation of the same disturbance at 

 outlying stations, from Toronto, from St. Helena, from the Cape of Good 

 Hope, nay, even from Trevandrum in Travancore. All these accounts ar- 

 rived in time to be inserted in the Report of this Association for 1841, and 

 it must surely be regarded as a signal proof of the efficiency of the arrange- 

 ments made on all hands, that a phsenomenon, casual in its nature so far as 

 we yet see, and manifested by no external and visible premonitory symptoms, 

 should have been thus seized upon by our observers in Europe, Asia, Africa 

 and America, reported thence to England, reduced, printed and circulated 

 in three months and a week after its occurrence. " Tantum series June- 

 turaque pollet" /* 



Anomalous magnetic movements of unusual magnitude take place on the 

 average 3 or 4 times in the month, but apparently with greater frequency 

 in some months than in others. The returns from the different stations 

 show hitherto without exception that these disturbances are general, that is 

 to say, that though the movements individually may not be, and in fact are 

 not, always simultaneous, the observations of the same day never fail to ex- 

 hibit unusual discordances at all the stations. Generally the disturbances 

 are characterized by a diminution more or less of horizontal intensity, pre- 

 vailing more or less for several hours together, everywhere, and mostly ac- 

 companied by a movement, also general, of the north end of the needle to- 

 wards the west. By a memorandum of Lieut. Younghusband on the disturb- 

 ance on the night of the 15th April 1842, which was so considerable that the 

 range of the declination in little more than an hour extended over 2° 15' in 

 arc, it appears that with the 15-inch bars used in the observatory, which re- 

 quire 17 s for a vibration, a change of more than 50 divisions of the scale, or 



* Dr. Lamont states that during the most intense part of this disturbance, (the whole of 

 which was observed by him at Munich,) the movements exhibited no correspondence, taken 

 seriatim, with those at Greenwich. 



