66 On Atmospheric Magnetism. 



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 de- 

 scribed 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 predominance 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 particu- 

 larly examined into and stated in the Philosophical Transac- 

 tions already referred to. The next step will be to ascer- 

 tain what is the amount of change in the conducting power 

 of the air for giving changes of temperature, and then to 

 apply that in the endeavour to ascertain whether the amount 

 of change to be expected is (as well as the direction) accord- 

 ant with that which really occurs. 



M. F. 



