MARYLAND GEOLOGICAL SURVEY 461

may possibly be due to the fact that the tabular results do not refer
in each case to the same interval of time and they were not deduced
by one common method.

MINOR PERIODIC FLUCTUATIONS.

Of these may be mentioned the variation depending upon the solar
rotation, having a period of about 26 days, and the variation depend-
ing upon the position of the moon with reference to the sun and the
earth. The ranges, or differences between extreme Values of both of
these variations, are so minute that it requires many years of con-
tinuous and carefully made observations to detect them.

MAGNETIC STORMS.

Generally speaking, these may occur at any time and are frequently
accompanied by auroral displays. Such storms may at times have a
very wide circle of action and occur practically simultaneously over
the whole area. Thus on December 3d, 1896, while I was on my
way to Salisbury to establish a meridian line for Dorchester county,
I saw in the evening a most brilliant aurora, and the next day while
making magnetic observations the behavior of my needle plainly in-
dicated that a magnetic storm was prevailing. I have since then
received from a magnetic observatory at Bochum, Germany, estab-
lished in connection with a mining plant, the tabulated hourly values
of the magnetic declination during 1896 and I find that the magnetic
storm of December 4 likewise made its appearance at this distant place.

The deviations caused by these spasmodic fluctuations in the earth's
magnetism may in these latitudes occasionally amount to as much as
10'-20' and even more. On October 12th, 1896, I made observa-
tions at Oakland at various times during the day. The diurnal varia-
tion on that day was completely reversed, the highest value occurring
in the morning, instead of in the afternoon, and the lowest value in
the afternoon, instead of the morning. My first observation in the
morning required a correction of —16'.

Small spasmodic fluctuations occur frequently. Thus, according to