TRANSACTIONS OF THE SECTIONS. 25 
ere 
_ bring to the ice portions of atmosphere saturated with moisture from sea-weed, most 
frequently accompany these auroral displays. 
Having endeavoured to trace the aurora to these localities, he concludes his paper 
by identifying these auroral zones with the existence of electrical currents and their 
application to the theory of terrestrial magnetism. He considers that these zones 
will not approach nearer to either pole of the earth than the margin of the fixed ice, 
from the absence of humidity in the atmosphere over the fixed ice; but that they 
will extend themselves indefinitely towards the equator, and also in height above the 
surface of the earth. And since the general configuration or curvature of the zones 
must obviously approximate to that of the isothermal lines, which latter are known 
to accord in a very remarkable way with the magnetic curves, he thinks there are 
good grounds for concluding that Ampére’s theory is founded in truth, and that these 
currents circulate within the zones from east to west; the exciting cause of the cir- 
culation of the currents in this direction being probably the action of the sun, as 
each portion of the zones is brought consecutively by the diurnal rotation of the 
earth within the solar influence ; the magnetic needle being thereby induced to place 
itself at right angles to the direction of the currents. It will follow also, that the 
electrical development in each zone will be greater in winter than in the summer of 
the corresponding hemisphere ; and that the magnetic force will also be a maximum 
in the winter time, which is found to be the case. 
He suggests, that upon the same principle the force,soliciting the horizontal mag- 
netic needle will be a minimum during that period of the day when the solar influ- 
ence is most effective in diminishing the electrical development in that part of the 
zone which is situated in the direction of the magnetic meridian ; that the diurnal 
deflection of the north end of the needle (as observed in Europe) towards the west 
in the morning, and the contrary motion in the afternoon, may be also thus recon- 
ciled; and, finally, that the aurora will produce a similar effect by restoring the 
electrical equilibrium, and cause a diminution of the magnetic intensity of the hori- 
zontal needle when a display happens in or near the direction of the magnetic meri- 
dian, and also a corresponding deflection in declination from that part of the zone 
where the phenomenon occurs. These conclusions the author has reason to believe 
are confirmed by observations. 
On the Measurement of T'wo Arcs of the Meridian in India, the middle point 
being in latitude 24° 7' 11", the southern extremity in latitude 18° 3' 15", 
and the northern in latitude 29° 30' 49". By Lieut.-Colonel Everegsr, 
F.R.S., §c., late Surveyor-General of India. 
| Colonel Everest described the apparatus employed in the measurement of three 
, 
. 
bases connected with this work, as also the instruments used in determining the 
celestial arcs of amplitude and in the terrestrial operations, and exhibited engravings 
illustrative thereof. 
i On a Lunar Meteorological Cycle. By Luxe Howarp, F.R.S. 
Mr. Howard reports that the facts of the last two years compel him to modify 
3 his anticipations as to the extent to which the lunar cycle will enable him or others 
_ to become “ weather prophets.”” But he says the deferred heat (to be expected from 
_ the corresponding period of the cycle in 1825 to 1828) may prove to be only de- 
_ feated cold; and the absence of so great an elevation of the mean temperature now, 
_ may spare us a repetition for many seasons to come of the cold which occurred be- 
_ tween the years 1835 and 1840. To show, however, that causes exist for these 
_ periodical alternations of warmth and cold, much more extended in their effects than 
_ any which are peculiar to our own climate, he proceeds in detail to place in review 
_ together the annual mean temperature for eighteen years (ending with 1823) at 
Geneva and London. It will be seen that the two cities differ little in their climatic 
or annual mean; the more southern latitude of the former being counteracted by its 
greater elevation above the sea. See Plate IV. 
4 
: 
iz, & 
