422 Prof. Kreil's Deductions from the first Year's Observations 



the two maxima, one in the forenoon and the other in the af- 

 ternoon, always occur, though in the summer months the 

 former is the most conspicuous, and in the winter the latter ; 

 the observations which I had previously made at Milan were 

 not sufficiently numerous to manifest the occurrence of this 

 noon-minimum. 



Observations made in May and June,1840, at 2 and 4 a.m., 

 show a maximum and minimum in the hours of the night, 

 which sometimes exceed those above-mentioned. 



In May, at 11 p.m. the maximum = 246*43 



at 2 a.m. the minimum = 244*49 



Difference ...... 1*94 



In June, at 11 p.m. the maximum = 267*73 



at 4 a.m. the minimum = 266*53 



Difference 1*20 



The circumstance already noticed, that these maxima are 

 in some months almost insensible, makes it difficult to recog- 

 nize the dependence of the hour of their occurrence on the 

 season of the year. 



The following numbers, which are the monthly means of 

 all the observations of the inclination made between 5 a.m. 

 and 10 p.m., will show to what considerable alterations that 

 element is subject in the course of a longer period. 



1839. August. Inclination = 368*06 



September. = 374*42 



October. = 366*42 



November. = 336*40 



December. » = 294*18 



1840. January. . — = 252*14 



February. — = 196*59 



March. = 182*91 



April. = 197*47 



May. = 245*59 



June. ' = 266*70 



If we compare these numbers with the means of the hori- 

 zontal intensity, we shall not, it is true, see any perfectly par- 

 allel march, which indeed we ought not to expect, as the 

 horizontal component depends on the total intensity as well 

 as on the dip ; but it is sufficiently clear that there is a ge- 

 neral accordance, the horizontal intensity increasing with the 

 decrease of dip, and vice versa: therefore the changes of 

 inclination indicated by the instrument are not to be ascri- 

 bed to mere alterations of the centre of gravity in refer- 

 ence to the point of suspension, but are, in part at least, 



