188 W. A. Norton on the Variations of the Declination 
It may be well to meet at the outset an objection that may oc- 
cur to some of my readers. It is implied in what follows (al- 
though not perhaps of necessity) that the atmosphere derives its 
principal electric excitement from a solar action upon its upper re- 
gions ; when it has generally been supposed hitherto that atmos- 
pheric electricity has its origin in the evaporation going on at the 
earth’s surface. But in fact t, the old theory of the origin of at- 
mospheric electricity has no longer any basis to rest upon. Ac- 
cording to Becquerel, and other able experimenters, electricity is 
a generated by He on unless salts are present in the water. 
e years since M. Riess and M. Reich showed that the elec- 
ainy attending diastiod proceeded from the friction of the 
water against the sides of the vase. This fact is proved anew by 
the researches just published of M. Gaugain, although the results 
differ in the details from those of the German physicists.” If the 
act be admitted that the atmosphere is electrically excited by some 
action of the sun, our views of certain meteorological phenomena 
must be modified, and we may derive new light with regard to 
some of these phenomena hitherto enveloped in mystery. 
It should be observed that the idea of the magnetic needle, at 
the earth’s surface, being disturbed by electric currents circula- 
ting in the upper regions of the atmosphere cannot be regarded 
as an hypothesis, since we know from observation that the needle 
is disturbed by the Aurora Borealis, and that this phenomenon is 
electric excitement, and electric currents, is the only known ter- 
restrial cause of magnetic disturbance. 
DECLINATION, 
It is to be recollected that the estiostion at any particular 
place may be either East or West; and that in the Southern 
Hemisphere, as well as in the Norio it is defined by the posi- 
tion of the North end of the needle with rene to the North 
point of the horizon. 
Diurnal Variations. 
The laws of the diurnal variations of declination are graphic- 
ally represented in the annexed diagram, (Fig. 1.) On examining 
it it will be seen that the needle has its He habe of declination, 
or in other words, that its north end has its most ane position 
a.M. At this hour it begins to move towar e west, 
and continues to do so until 1 p.m., when it has icacd to its 
maximum of westerly deviation. It now begins to return tow 
the east, or its declination decreases, and this movement continues 
until 10 p.m. when there is a second minimum of declination. 
Hemnl0 Pmt Rx, there isa ly movemen 
