490 
THE ASTRONOMER ROYAL’S EXPERIMENTS 
4. The law of effect of a soft iron bar surrounded by a galvanic coil differs, but not 
greatly, from that of the large magnet presenting its edge. It would seem not impro- 
bable that this may depend partly on the effect of the coil which incloses the iron bar ; 
and, if so, the law for a soft iron bar approaches still more to that of a magnet. 
5. The exhibition of the effect of the magnetic coil alone is worthy of careful exami- 
nation. The first thing which will strike the eye is the astounding increase of power 
produced by the insertion of the soft-iron core. At the sides of the magnet, where the 
measures of force for the coil alone are T5 and 1-8, those for the coil with core inclosed 
are 164-0 and 310-0; at the ends, where the coil alone gives 5-75 and 22-5, the coil 
with core included gives 227"0 and 840-0. 
6. The law of magnitude of forces for the coil alone differs greatly from that of a 
steel magnet. In the inner circuit the proportion of the force at the end to force at 
the middle of length is, for the steel magnet fyf , for the coil ; in the outer circuit 
they are and fff. 
7. Still more remarkable is the difference in the law of direction of the forces near 
the ends. Using the term “ pole” to denote that point near the extremity to which the 
directions of forces rudely converge, the pole of the steel magnet is within the magnet, 
and distant from the end by about of the magnet’s length : but the pole of the 
galvanic coil is absolutely at its end ; indeed some of the experimental directions of 
force fall a little beyond the end. 
It is evident, from the remarks of Nos. 6 and 7, that a magnet cannot in any wise be 
represented as a system of revolving galvanic currents, with an equal number of circuits 
at every part of its length. 
With the view of presenting the results in the form which may probably be found 
most advantageous for comparison with the conclusions from any future theory, I have 
resolved the forces into rectangular directions, parallel and transversal to the axis of 
each magnet, by the following graphical process. Upon each mean line of direction of 
force (ascertained as is described above) I have laid down the mean measure of the force 
(as found above), and upon this measure as hypotenuse I have constructed a right-angled 
triangle, the lengths of whose sides give the two forces. From the nature of the pre- 
ceding operations, it is only necessary to form these numbers for one quadrant of each 
magnet. The results are given in the following Tables. The centre of the large 
magnet or coil is in every case the origin of coordinates of the external magnetic point 
on which the action of the large magnet &c. is estimated — the axis of the longitudinal 
ordinate being the axis of the magnet, and the axis of the transversal ordinate being 
normal to it. The powers are estimated as those of the red end of the large magnet 
operating on a small external mass of red magnetism. It will be remembered that, for 
the galvanic coil without core, all the numbers must be divided by 120. 
