nnd Remarks on the Theory of Magnetism, it\ 



cup, which I conceived might possibly increase its sensibility, 

 by creating a slight degree of electricity or galvanism. This 

 combination of metals also moved regularly to the apparent 

 motion of the sun, and continued to vacillate as long as the rays 

 of the sun impinged upon the metals ; the vibrations diminish- 

 ing and encreasing with the sun''s altitude, being greatest when 

 the sun was near the meridian, and decreasing as the number 

 of the degrees decreased that the sun was above the horizon. 



The next form of the instrument I tried, was twenty-five 

 needles fully impregnated with the magnetic fluid, fixed into a 

 circular ring of cork, of about three inches diameter. They 

 were placed at equal distances round the circumference of the 

 circle, with their north and south poles placed outwards alter- 

 nately. This circle was affixed to a light slip of wood, five in- 

 ches long, and one-fourth inch broad, by a piece of copper- wire, 

 of a semicircular form, the extremities of which passed through 

 the opposite sides of the cork circle ; and the slip of wood was 

 attached to the centre of the wire. Into the centre of the bar 

 of wood was fixed an agate cap ; and the whole traversed like a 

 compass needle upon a fine steel point, the bar of wood being 

 equipoised by a small weight at the other end of it, equivalent 

 to the weight of the needles (as represented by fig % PI. I.) 

 This instrument was placed under a glass cover, of a conical 

 shape, and secured from any passage to the air. 



When first exposed to the sun's rays, the instrument con- 

 tinued to revolve upon the pivot for several hours, and then 

 settled with one side of the circle pointing toward the sun, in 

 such a position that one-half of the external part of the circle 

 was illuminated by the solar beams, and one-half of the internal 

 part of the ring. In this situation it continued to stand still, in 

 opposition to the diurnal motion of the earth, till the sun sunk 

 beneath the horizon ; the points of the needles on the edge of 

 the circle pointing always to the sun, so that the solar rays fell 

 in a direction nearly parallel to the plane described by the star 

 of needles. 



This instrument (like all other magnetical instruments that I 

 have made experiments upon) accommodated itself to the pecu- 

 liarities of its construction. For the magnetic needle, when 

 placed in any situation that may be termed new to it, in respect 



