606 LAMONT: MAGNETIC RESULTS 
11 a.m., then increase until between 12 and 4 p.m.; then follows 
a wave-like course, in which the summits of four waves may be 
distinguished ; the first of these is quite short, and its highest 
point occurs in the summer months immediately after 3 P.m., 
and in the remaining months rather earlier; the summit of the 
second is on an average at 8 p.m.; the third shows a small rise 
between midnight and 2 a.m., and the fourth usually occurs 
about the time of sunrise. 
The mere aspect of the curves of intensity, as well as those of 
declination, is sufficient to show that the diurnal march of the 
magnetic variations does not depend on the sun only; it appears 
highly probable that regular oscillations of the magnetic ele- 
ments take place independently of the influence of the sun. 
It should be remarked, that the magnets employed have been 
constantly losing force in a ratio not yet determined with suffi- 
cient precision to be introduced into the calculation ; the uncer- 
tainty in the determination of the diurnal march due to this 
cause is however limited within very narrow bounds. 
By combining the variations of the declination with those of 
the horizontal intensity, we obtain the configurations in the ac- 
companying Plate, where the movement in the day is repre- 
sented by dotted, and in the night by continuous lines. 
It is not improbable that the total force of terrestrial magne- 
tism may remain unchanged, and that the variations may relate 
to direction only, so that the fluctuations of the inclination 
would be given by those of the horizontal intensity. Under this 
supposition the drawing would represent the movement of the 
north end of a needle freely suspended in the direction of the 
earth’s magnetic force. 
We see that in summer the curve has some resemblance to 
two ellipses, the greater of which is passed over in the day, and 
the lesser in the night. The astronomical meridian is perpen- 
dicular to the major axes of both ellipses. In winter the curves 
become far more complicated, yet so that the transition in the 
form of the curve from one month to the next may be traced. 
Absolute Horizontal Intensity, its Annual Period and Secular 
Change. 
Table VII. gives the monthly means of the absolute hori- 
zontal intensity calculated from the two-hourly observations ; the 
elements employed in the reduction (particularly the daily loss 
¥ 
