1851.] OF THE ROYAL INSTITUTION. 59 
in Mr. Faraday’s paper in the Philosophical Transactions for 1851, 
Part I. Par. 2843, &c. 
Now this by the hypothesis is assumed to take place in the atmo- 
sphere. Supposing it all at mean temperature, the lines of force 
would have the direction determined by the arrangement of the 
power within the earth. Then the sun’s presence in the east would 
make all the atmosphere in that region a worse conductor, and cause 
it to assume the character of D; and as the sun came up to and 
passed over the meridian and away to the west, the atmosphere 
under his influence would bring up changes in direction like those 
shown in either D or D; it would therefore manifestly set a needle 
in a given latitude in opposite directions as it passed by; and as 
evidently set two needles in north and south latitudes in opposite 
directions at the same moment of time. As the night came on and 
a temperature lower than the mean came up from the east and 
passed over, the lines of force would be inflected as in P or P., and 
a reverse variation of the needle to that which occurred before 
would now take place. 
That natural effects of variation must be produced consequent 
upon the magnetic nature of oxygen and its daily variations of tem- 
perature is manifest ; but whether they cause the observed variations, 
or are competent to do so, is a question that can only be decided 
after very careful enquiry. Observations are now made on the 
surface of the earth with extreme care in many places, and these are 
collated, and the average or mean result, as to direction and intensity 
of the earth’s force, ascertained for every hour and season; and also 
many remarkable, anomalous, and extra results evolved. A theory of 
_ the causes of any or all of these variations may be examined first by 
the direction which the varying needle does or ought to assume, and 
then by the amount of the variation. The hypothesis now brought 
forward has been compared with the mean daily variation for all the 
months in the year at north and south stations, as Toronto and 
Hobarton, and at many others near to and far from the Equator, 
and agrees in direction with the results observed far beyond what 
the author anticipated. Thus the paths described by the upper ends 
of free needles in the north and south hemispheres should be closed 
curves, with the motion in opposite and certain directions, and so they 
are :—the curves described by needles in north or south latitudes 
should be larger in summer and smaller in winter, and so they are :— 
a night or cold action should grow up in the winter months, and such 
is the case :—the northern hemisphere ought to have a certain pre- 
dominance over the southern, because of its superior temperature, 
and that is so:—the disposition of land and water ought to have an 
influence, and there is one in the right direction :—so that in the 
first statement and examination of the hypothesis it appears to be 
remarkably supported by the facts. All these coincidences are 
particularly examined into and stated in the Philosophical transactions 
already referred to. The next step will be to ascertain what is the 
