at the Magnetic Observatory at Prague. 423 



due to the altered direction of the force itself. It would 

 seem then that the dip is subject to much greater alterations 

 than has been hitherto recognized; and this is quite con- 

 ceivable, if we suppose temperature to be one of the chief 

 causes of the variation of the magnetic elements ; for if the 

 daily progress of the temperature from east to west produces 

 the large diurnal variation in the declination, its annual march 

 from south to north, and vice versa, ought in like manner to 

 occasion an annual variation in the inclination. 



4. The times of oscillation of the dipping needle showed 

 during the winter, 



s. DifF. 



At 8 a.m. a maximum = 12-86978 



At 10a.m. a minimum = 12-85321 



At 2 p.m. a second maximum = 12-86923 on9inn 

 At 8 p.m. a second minimum = 12-84-823 



In summer, 



At midnight, a maximum. 



At 6 p.m. a minimum s= 12-55078 O-0935Q 



At 2 p.m. a second maximum = 12-57437 

 At 9 p.m. a second minimum = 12-56605 



The midnight maximum was shown by the night observa- 

 tions of May and June. 



The dependence of the hours of maximum and minimum 

 on the season could not be recognized with certainty from 

 the observations of each month separately considered ; it ap- 

 peared, however, as if those of the forenoon observed in winter 

 approached progressively nearer to noon. 



The following are the monthly means of all the observa- 

 tions made from 5 a.m. to 10 p.m. 



s. 



1839. August. Timeofvibr. =12-02318 



September. = 11-86037 



October. = 11-78188 



November. = 11-90803 



December. ~ 12-69148 



1840. January. = 13-36133 



February. = 13 '4086 7 



March. = 14-00672 



April. = 13-76645 



May. = 12-77688 



June. = 12-39025 



From these numbers, which are not corrected for the in- 

 fluence of temperature, or for any decrease in the magnetism 

 of the bar, we cannot trace a connexion with the tempera- 

 ture, such as has been usually supposed to exist, viz. a de- 



