330 = =©Prof. W. A. Norton on the Diurnal and Annual 
“Arr. XXIX.—On the Diurnal and Annual dyes in the 
Declination of the Magnetic Needle, and in the Horizontal 
and eee oawate Intensities ; by Prof. W. A. Norton. 
In my: paper on’ the heaped Fariaticng of the Magnetic ele- 
ments, published in a former No. of this Journal,* I showed that 
the variations of the heriaeritih magnetic intensity which lie 
between the hours of 10 p. m. and 10° a.m. of the,following day 
proce eed pari passu, and are undoubtedly in some way physically 
3 connected with the variations that take place during the same 
~. Interval of time in nk quantity of moistute immediately at the 
: ‘éarth’s surface :—or at all events that the deviations from the 
~ eneral law of spominionalicy to temperature that oceur during 
this interval are effects, direct or indirect, of the deposition of 
dew ‘during the night, and evaporation of moisture during Mec 
morning hours: re ‘agcounted for the connection subsisting bey 
4 tween such dissimilar phenomena by assuming that particles: - 
water in Gontact with the earth’s surface, (and possibly in t 
~ vaporous state,) hada direct magnetic action upon the needle, in 
accordance with the general theo ory that I had advanced. This” 
1s bi simplest assumption that can be made in the case, but It. 
to be observed that the connection in question may possibly be - 
sd 
A cae 
x 
as is well known, is. eittandant upon : | 
varying conduction. of electrical currents, or ‘some other cause. 
For the present, however, it is most» philosophical to abide by | 
that view which gives us the: highest generalization—which rep-— 
resents, at the same time, ‘the nor rmal state of the earth's DA 
netism and its periodical variations. 
It is true that we have no authority, » derived: Sonik exec 
for st su Ipposing water to have a Sects action, as. Ee te rm gay 
0 
the earth, has what is called a diamagnetic action:’ But our first 
aim in such ~~ should be to obtain the highest generaliza- 
om the discussion of the phenomena mere ve 
the same great truth. I would also remark, with regard to the 
bate discussion, incidentally entered into in the paper 
rred to, —. the thermal effect of dew, that this 
peste mae perhaps ha ve been overrated, and that the law of the 
pee oe Lee es 
* See this Journal, ii ser., vol. viii, p. 35. 
