and Directive Force of the Magnetic Needle. 187 
the wpper atmosphere. : 
Before entering upon a particular examination of the diurnal 
are the same in different parts of the earth. The following are 
the principal results which have been obtained on this point : 
l. The laws of the diurnal variations are essentially the same 
at all places to the north of the Torrid Zone; they are also the 
‘he laws are the same in the Southern Hemisphere with- 
out the Torrid Zone, as in the Northern, if we observe that in 
same local hours the north end of the needle is moving in oppo- 
Site directions at stations in the two hemispheres, without the 
tropics. 
_3. At stations situated between the Tropics, the laws of the 
diurnal movement are not the same throughout the year, as they 
are very nearly in other parts of the earth; at certain local 
hours the needie moves in the one direction or the other accord- 
ing as the sun is north or south of the equator. 
may here state that the theoretical views advanced in the 
togress of the present discussion all have their foundation in one 
€nt points of observation, and which will equally well explain 
the laws of all the variations of the horizontal and vertical forces. 
IE so, it can hardly be doubted that the hypothesis is either a ver- 
itable reality, or has its counterpart or equivalent in nature. If 
_ itstands the test of quantitative determinations, the conviction 
_Of its truth will be strengthened 
