340 Prof. Wie sah aga on the Diurnal and Annual variations, §c 
and that the sania ditbi is such as our theory calls for. The 
question of this connection cannot however be definitively settled 
until we have’ obtained a ar series of observations, and at a 
Beater number of places. ; 
= te Moats wale oti General Results. . 
Tt may be well to ‘recapitulate here’ ie brain important results 
arrived at in this and‘the previous memo , 
1. The diurnal and aniual variations of the horizontal _mag- 
 hetic intensity are’due to the joint operation‘of two general an- 
: sp rermiatis causes, V1Z., variations of temperature and variations of 
ae 
The’ diurnal and® annual variations of the‘height of the 
: Seltin (or pressure of the air) are attributable to a Sang: 
ie * general causes ;—with this probable ditference, that in ASE 
the effects result. directly from changes in the teapereaatl “and 
‘humidity of-the air, and in the other from changes: in the tem 
eer and humidity of the earth’s surface 
Sta Sieben of horizontal mate intensity and of bar 
thie t 
#6), be heared: variate of the jioctaaal magnetic oe 
es ae gonsequences of the thermal theory of t 
ial-maghe hting that moisture has a magnetic ion; 
ons the Variations of the horizontal force, 
e get 
fications ae deed: ‘by the. deposition of vapor aye 
ages “evaporation of the ‘same {from the-eart a 
0 thee ease a the diurnal variations the : effiécis: ee ‘the mean 
of three months’ variations) are confined chiefly ‘to th ag 
between sundown and the hour of: 10 a.m. on the: tolls ' 
e 6. Taking the mean for three’ months, bees au 
erease of the horizontal force during the 
iefly upon the quantity of rain that falls. ‘The “easpination <j 
_ of this dependence is that the. diminution of this force Lae 
: morning j is owing to the evaporation, which then ocers, “an 
Average amount of this evaporation’ must: be mainly. dependent 
upon the average quantity of rain that falls. 5 
7. The deposition of dew at night which has the effect ae 
check, and even overcome the diminution of the horizontal force, 
due to the fall of the temperature, exerts also an important influ- 
ence in moderating the nocturnal decrease of temperature, which’ 
does not appear hitherto to have been recognized. T | 
* See this Journal, 2nd ser., vol. viii, Number for Nov, 1849, p. 358. a 
{ See this Journal, 2nd ser, yol. viii, Number for Sept., 1849, p- pate a” 
