57 
the intensity of magnetic forces ^ &c. 
I obtain the values of M in terms of F, at those hours ; and 
dividing each of these values by the minimum value of M, 
I find, as before, the relative terrestrial magnetic intensities 
at the times of observation. 
D. _ Table of the mean Terrestrial Magnetic Intensities at diffe- 
rent hours during the day, deduced from the 'preceding observa- 
tions. Note. The observations were made in the open air. 
Time of 
Mean of the Observations of 
June 20 , 21 , 22 . 
Observation. 
Azimuth of the 
Point of Equilibrium. 
Terrestrial 
Magnetic Intensity. 
h. m. 
6 OO 
79 30.0 
1.001 12 
7 30 
79 51.7 
1.00061 
9 OO 
80 24.7 
1.00028 
lo 30 
80 42.2 
1.00000 
Noon. 
80 32.7 
1 .00015 
1 30 
79 23.0 
1 .00134 
3 OO 
78 53.2 
1.00188 
4 30 
78 34.8 
1.00223 
6 OO 
78 20.3 
1.00251 
7 30 
78 26.5 
1.00239 
9 OO 
78 42.3 
1.00209 
From these it appears, that the minimum intensity hap- 
pened nearly at the time the sun passed the magnetic meri- 
dian, and rather later than in May, which was also the case 
with the time of the sun's passage over the meridian the 
• The diurnal variation, both in the direction of the needle and in the magnetic 
intensity, appears to have a reference to the position of the sun with regard to the 
magnetic meridian ; it is therefore probable, that the sun is the principal cause of both 
MDCCCXXV. I 
