Royal Listitution, 313 



austral pole dipping in north magnetic latitudes, and the boreal pole 

 dipping in south magnetic latitudes j was explained. It was also 

 shown experimentally that this is generally analogous to what hap- 

 pens when a small magnet is subject to the action of a large one; 

 and, theoretically, that this is a consequence of the attractions and 

 repulsions of poles (the magnitude of the forces being inversely as 

 the square of the distance, — a law which from various considera- 

 tions is established with the utmost certainty). He adverted to the 

 mechanical composition of forces, and showed that, from the dip 

 and the horizontal force, the whole magnetic force might be found. 

 And he stated that, on approaching the magnetic j)oles of the earth, 

 namely, those points to which (as observed at no great distance) the 

 needle converges on all sides, and on approaching which, the direct- 

 ive force becomes smaller to evanescence, and the dipping-needle 

 dips more and more till it is vertical, the whole magnetic force does 

 not diminish, but increases nearly to its maximum. 



Then, were pointed out the construction of Gauss's bifilar magnet, 

 in which the magnet is strained to a position at riglit angles to that 

 of the free magnet, by the torsion of position of its two suspending 

 threads, and every change in the magnitude of the horizontal mag- 

 netic force is shown by the position of the magnet, which is pulled 

 more or less in opposition to the torsion ; — and the construction of 

 Lloyd's vertical-force magnet, in which a magnetical bar, mounted 

 like a scale-beam, is loaded to a position of horizontality, and every 

 change of the vertical part of the magnetic force is shown by the 

 position of the magnet, which is inclined more or less in opposition 

 to the preponderating weight. 



Allusion was then made to the organized system of observations 

 of magnets at every five minutes of Gdttingen time on certain days 

 in the year (Sundays), first established by Gauss, with the assistance 

 principally of students of the German universities, but afterwards 

 extended to other parts of Europe; and to the enormous extension 

 of the system, principally by the Russian and the British Govern- 

 ments and the East India Company, over every part of the world 

 (the simultaneity of observations and the use of Gottingen time being 

 retained throughout, but the days of the five-minute observations 

 being changed from Sundays to week-days); and to the Magnetical 

 Expeditions which, with the establishment of distant magnetic ob- 

 servatories, constitute a national enterprise inferior to nothing but 

 the French expeditions of the last century, and to the perfection of 

 the organization and the improvements in the instruments and the 

 mode of using them, especially at sea, which has been introduced 

 by Col. Sabine. 



The lecturer then pointed out the general character of the results. 

 As regards the mean or average determinations (omitting the slow 

 or secular changes, and deferring for a moment the rapid changes), 

 nearly all collectors of results for declination, from the time ofMal- 

 ley, had conceived the existence of four magnetic poles : — two (the 

 Hudson's Bay pole and the Australian pole) having been nearly 



PhiL Mag. S. 3. Vol. 36. No. 243. April 1 850. Y 



