978 Transactions of the American Institute. 



of the magnetic force is produced and regulated by forward revo- 

 lution. 



That the attraction of the needle is to the center of the earth, I 

 think is shown by a variety of circumstances. First, the shape of 

 the globe is such that direct rays falling upon its surface necessa- 

 rily concentrate at its center, and the attracting force would seem 

 to be of that character; and secondly, if a needle be magnetized 

 in but one end, that end will point downward towards the center, 

 though not at all increased in weight; but if both ends be mag- 

 netized, and the needle balanced to a horizontal jiosition, it then 

 points in the direction of a line icith the magnetic current. For the 

 same reason that the attraction is to the center, if a compass be 

 placed near the magnetic pole and compelled to keep its horizontal 

 position, it refuses its duty, and will turn every way at random; 

 but if left to itself, its point tends downward towards the center 

 of the earth, and this is what is called in navigation " the dip of 

 the needle," which increases always as you approach towards the 

 pole. 



From these circumstances it has been sometimes assumed that 

 the interior of the earth is a powerful natural magnet; and even 

 with my theory it is so, though not in the sense as has been sup- 

 posed; for it will ))e seen at once that, if the attraction were to the 

 center of the earth, by a fixed magnet, then there could be no 

 change of variation in the same locality; and as we have seen that 

 such change does take place, that theory is at once exploded. 



We prefer, then, to follow our own choice, and assume that the 

 direction of the needle to the pole is only an indicator of a line of 

 hio-her attraction; and that the immediate motive power is a con- 

 centric magnetic force; rendered active, and mvolved by revolution. 

 Let us see then what will be the result. 



We will suppose that the revolution of the earth on her axis is 

 the governing cause, or controlling force, the attraction being to 

 the center of the earth; then the needle being balanced to a hori- 

 zontal position, would always, in all places, point due north and 

 south, in a line with the center of motion, wliich it never does, 

 except in two places at a time (the antipodes of each other and 

 through their lines of longitude); and there could then be no revo- 

 lution of the magnetic pole, and no variation or change of variation. 

 We must, therefore, look further for our evidence in support of the 

 truth of our position. 



Let us suppose, then, that the earth's revolution round the sun 



