NATURAL PHILOSOPHY. 123 



Halley's time, accompanied by a corresponding change in the positions and 

 forms of the isodynamic, isoclinal, and isogonic lines in North America; a 

 careful determination of the absolute values and present secular change of 

 the three elements at this critical theoretical epoch, at stations situated on 

 either side of the American continent, and nearly in the geographical 

 latitude of the maximum of the force, would furnish, therefore, data for 

 posterity, of the value of which we may have a very inadequate appreciation 

 at present. 



ON THE DEVELOPMENT OF A PHYSICAL THEORY OF TERRESTRIAL 



MAGNETISM. 



At the last meeting of the British Association, Mr. J. Drummond presented 

 a new theory of terrestrial magnetism, an outline of which he submitted to 

 the meeting for '57. (See Annual Scientific Discovery 1858, page 370. ) The 

 fundamental principles of this theory are as follows : Assuming the prevail- 

 ing idea regarding the early condition and present state of the globe, viz., 

 that it has cooled down from a state of fluidity, and now consists of a solid 

 crust inclosing a molten nucleus the author assumed also that the sun, 

 moon, and other planetary bodies, must exert the same influence upon the 

 inclosed fluid which they exert upon the surface ocean in producing the 

 tides, that, consequently, a system of internal tides must be occasioned 

 simultaneously with the external tides. Further, accepting the theory of 

 Gauss, that the entire matter of the globe is magnetic, he concluded that 

 the passage of these internal waves must occasion corresponding changes 

 in the position of the needle; and, reasoning from these premises, he arrived 

 at the following conclusions in regard to the changes in position which the 

 needle ought to undergo, decimation needle at any station, resting on 

 the line of the magnetic meridian, ought, upon one of the internal waves 

 coming from the eastward, to make an excursion to meetjt ; as the crest of the 

 wave approaches the station of observation, the needle ought to return with 

 ; t; and when it comes immediately beneath .he point of observation, the 

 needle ought to coincide - ain with the meridian. As the wave proceeds 

 westward, the needle ought to follow it, making a westerly excursion equal 

 o the easterly ; and as the wave passes further west, and its influence over 

 he needle thereby declines, the latter ought slowly to return again to the 

 meredian. Again, an inclination needle ought to begin slowly to dip as the 

 crest of the wave approaches the station of observation, reaching its maxi- 

 mum when the wave is immediately beneath it, and slowly rising to its 

 former position as the wave passes easterly; and the intensity, as indicated 

 by the oscillating needle, ought to increase as the crest of the wave ap- 

 proaches the station, reaching its maximum when it is immediately beneath 

 it, and decreasing gradually as the wave proceeds to the westward, the max- 

 imum of intensity thus coinciding with the maximum of inclination. The 

 results of observation, Mr. Drummond stated, harmonize completely Avith 

 the conditions of the theory. 



INFLUENCE OF MAGNETISM OVER CHEMICAL ACTION. 



The following inquiry, by Mr. H. F. Baxter, originated in an endeavor to 

 ascertain whether Magnetism possessed any influence over Organic Forces ; 

 and the kind of experiments that were undertaken for the purpose of solving 

 this question, was that of submitting seeds during vegetation to the influence 

 of magnetism. These experiments, however, having failed to give anv 



