174 ANNUAL OF SCIENTIFIC DISCOVERY. 



at first sight opposed namely, the absolute simultaneity of magnetic dis- 

 turbances at all parts of the earth, and their predominance at certain local 

 hours at each place. General Sabine accounts for this apparent discrepancy 

 by the circumstance, that the hours of maximum disturbance are different 

 for the different elements ; so that there may be an abnormal condition of 

 the magnetic force, operating at the same instant over the whole globe, but 

 manifesting itself at one place chiefly in one element, and at another place 

 in another. I would venture to suggest, as a subject of inquiry, whether 

 the phenomena which have been hitherto grouped together as " occasional " 

 effects, may not possibly include two distinct classes of changes, obeying 

 separate laws one of them being strictly periodic, and constituting a part 

 of the regular diurnal change ; while the other is strictly abnormal and simul- 

 taneous. If this be so, it would follow that we are not justified in separating 

 the larger changes from the rest, merely on the ground of their magnhu le, 

 and that a different analysis of the phenomenon will be required. The 

 effects hitherto considered are all referrable to the sun as their cause. Prof. 

 Kreil discovered, however, that another body of our system namely, our 

 own satellite exerted an effect upon the magnetic needle, and that the 

 magnetic declination underwent a small and very regular variation, whose 

 amount was dependent on the lunar hour-angle, and whose period was 

 therefore a lunar day. This singular result was subsequently confirmed by 

 Mr. Broun in his discussion of the Makerstown Observations ; and its laws 

 have since been fully traced, for all the magnetic elements, by General 

 Sabine, in the results obtained at the Colonial Magnetic Observatories. 

 The foregoing facts bear closely upon the debated question of the causes of 

 the magnetic variations. It has been usual to ascribe the periodical changes 

 of the earth's magnetic force to the thermic action of the sun, operating 

 either directly upon the magnetism of the earth, or affecting it indirectly by 

 the induction of the thermo-electric currents. Here, however, we have a 

 distinct case of magnetic action, unaccompanied by heat ; and the question 

 is naturally suggested, whether the solar diurnal change may not also be in- 

 dependent of temperature. The most important fact, in its bearing upon 

 this question, is the existence of an annual inequality in. the diurnal variation, 

 dependent on the sun's declination, recently pointed out by General Sabine. 

 If we deduct the ordinate of the curve which represents the mean diur- 

 nal variation for the entire year, from those for the summer and winter half- 

 yearly curves respectively, the differences are found to be equal and opposite ; 

 and the curves which represent them are, consequently, similar, but oppo- 

 sitely placed, with respect to the axis of abscissa?. From this, General 

 Sabine draws the inference, that the diurnal variation is indirect effect of solar 

 action, and not a result of its thermic agency. Pres. LoycVs Address before 

 the British Association. 



ON THE ORIGIN AND CAUSE OF THE AURORA BOREALIS. 



At the Montreal meeting of the A. A. A. S., Prof. Olmstead presented briefly 

 his views respecting the origin and cause of the aurora borealis. Contrary 

 to the opinion which ascribes it to terrestrial agents, as electricity or magnet- 



