the Directive Power of Magnets, §c. 

 Galvanic Coil. 



229 



For attracted point, j 



Coil with 



iron core. 



Coil without core. 



Longi- 



Trans- 



Longi- 



Trans- 



Longi- 



Trans- 



tudinal 



versal 



tudinal 



versal 



tudinal 



versal 



ordinate. 



ordinate. 



force. 



force. 



force. 



force. 



00 



2-26 



-310 







- 216 







1-34 



2-26 



-286 



+ 169 



- 240 



+ 38 



2-68 



226 



-252 



+327 



- 315 



+ 120 



402 



2-26 



-193 



+ 477 



- 450 



+ 325 



53) 



2-26 



- 42 



+ 632 



- 550 



+ 848 



67 



226 



+ 162 



+562 



- 80 



+ 1480 



778 



1-70 



+380 



+420 



+ 1010 



+ 1630 



8-2 



074 



+ 790 



+296 



+2480 



+ 1170 



00 



373 



-164 







- 134 







1-34 



373 



— 132 



+ 82 



- 189 



+ 41 



2-68 



373 



-124 



+ 119 



- 200 



+ 104 



402 



3-73 



- 88 



+201 



- 217 



+ 212 



5 36 



373 



- 19 



+226 



- 123 



+ 383 



67 



373 

 3-44 



+ 39 



+214 



- 57 



+ 424 



7-83 



+ 94 



+ 176 



+ 100 



+ 436 



8-82 



2-8 



+ 134 



+ 149 



+ 264 



+ 410 



949 



1-82 



+ 186 



+ 99 



: + 475 



+ 338 



97 



0-73 



+223 



+ 44 



+ 668 



+ 186 



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. 



It does not appear possible to infer from these numbers, by 

 any direct analytical process, the law of distribution of magne- 

 tism in the bar. It must be done, I believe, synthetically, by 

 assuming a law, and computing the forces which would result 

 from that law, and then comparing these computed forces with 

 the forces actually observed. The only law which I have tried 

 is the supposition that the intensity of magnetism is propor- 

 tional to the distance from the centre of the magnet, which in- 

 cludes also the law that there is a gradual increase of red 

 magnetism from one end and a gradual increase of blue mag- 

 netism from the other end. Putting / for the half-length of 

 the magnet, a and b for the longitudinal and transversal ordi- 

 nates of the attracted point, x for the longitudinal ordinate 

 (measured from the centre) of any attracting point, and sup- 

 posing the magnet to be a line, it is easily seen that the quanti- 



