M. KreiPs Magnetic Observations. 243 
greatest near the time of the summer solstice and least in 
December. 
4. The intensity of the horizontal force increases from Ja- 
nuary to June, and decreases from July to December. 
5. The declination begins to increase at 8 in the morning, 
and increases rapidly until 1 or 2 in the afternoon, when it 
attains its highest amount; it then decreases more slowly until 
it reaches its lowest value : in the winter months the declina- 
tion is usually less at 11 in the evening than at 8 in the morn- 
ing, but only occasionally so at other seasons of the year. 
6. The mean value of the difference between the greatest 
and the least declination is 12' 2". The difference is greatest 
in the month which follows the vernal equinox, and least in 
December. 
7. This diversity is the consequence of the annual change 
in the declination, which at different hours in the day follows 
an opposite course ; in the forenoon, it decreases in spring 
and increases in autumn ; in the afternoon, it increases in 
spring and decreases in autumn ; hence it follows that there 
must be some hour in the day which is free from the annual 
change in the declination and which is therefore most suitable 
for insulated experiments. At Milan and at the present epoch, 
this hour is between 10 and 1 1 a.m. 
8. The total force attains its least intensity at 8 in the 
morning or earlier, and its greatest intensity between 1 and 4 
p.m. We are still in want of a sufficiently extended series of 
observations to furnish with equal certainty other facts re- 
lating to this element. 
9. The inclination increases in the morning till towards 
10 o’clock, when it decreases, but not uninterruptedly, for it 
increases again in the afternoon, and at 4 attains a second 
maximum, after which it decreases without interruption till 
near midnight This alteration in the inclination retards the 
time of the maximum and minimum of the horizontal force 
by two or three hours ; and its second maximum explains the 
anomaly mentioned in No. 1. 
10. The amount of the alteration of the inclination seems 
to be also dependent on the season of the year. A greater 
alteration (above a minute) was observed in summer, and a 
less (about half a minute) in winter. 
11. The times of the absolute maximum and minimum are 
very variable, but even in this variability a law is plainly ma- 
nifest. In January and February the maximum was observed 
at 4. 30' p.m., in March and April at 10. 30' a.m., from May 
to August at 8 a.m., in September and October at 10. 30' 
a.m., in November at 1 p.m., and in December at 4. 30' p.m. 
R 2 
