250 M. Kreil's Magnetic Observations. 



tends also to the total force. The needle in our inclina- 

 torium completes one vibration in nearly 14 seconds : during 

 the disturbance of the 17th of January 1838, it underwent an 

 alteration of O^'OT^. In February of the same year the mean 

 of the observed times of vibration for the month was 13"*874, 

 but for the 21st day of the month it was 13"932. I need not 

 remark how important it would be to examine such kindred 

 phaenomena as those of the atmosphere and auroras, with the 

 same exactness which is now applied to magnetic investi- 

 gation. 



I must mention one other phgenomenon which claimed our 

 attention in a very high degree, and which perhaps may 

 deserve that of other observers. I mean the vertical oscilla- 

 tions which show themselves so often in the dipping-needle, 

 and which also appear to be connected with determinate laws. 

 At least they are much more frequent in November and De- 

 cember than at other seasons, and they occur most commonly 

 in wet weather. For this reason I do not think that they can 

 be ascribed to a tremulous motion of the building, from which 

 the part of it which contains the apparatus is quite free. 

 Neither can they be attributed to the effect of currents of air, 

 because they occur less frequently at the time of the equi- 

 noctial gales and other storms than at the above-named 

 times. Perhaps they arise from very weak shocks of earth- 

 quake, which may be revealed to us by this highly sensitive 

 apparatus, and which probably occur much more frequently 

 than the more considerable shocks which are recognised by 

 our senses, and by other effects. At least the greatest vertical 

 oscillations of the needle have almost always coincided with 

 considerable earthquakes, often having their seat in remote 

 countries. One striking instance of this kind, after we had 

 experienced other similar ones, occurred on the 23rd of Ja- 

 nuary 1838. Between 1^ 33'^ and 7'' 47°^ p.m., Milan mean 

 time, the needle began to oscillate so strongly that its arc of 

 vibration appeared, by the vertical scale attached, to amount 

 to 27 millimeters, or nearly 10 minutes of arc; there were no 

 other indications of an earthquake of any kind. Twenty days 

 afterwards the newspapers contained accounts of considerable 

 damage caused by an earthquake on the same evening at 

 Bucharest, Jassy, Odessa, and other places. According to 

 these accounts the shock was felt at Jassy at 7'* 42™, and at 

 Odessa at7'' 45'" Milan mean time, agreeing with the beginning 

 of the phsenomenon observed by ns. 



Milan, Jan. 9, 1839. 



