298 Mr HARRIS'S Experimental Inquiries concerning 



33. In the experiment just described (31), the increments of 

 the attractive force of the magnet were necessarily very small, 

 since they depended exclusively on the iron, which had no per- 

 manent magnetism, and which operated at the distant pole. In 

 order, therefore, to allow of an increased action, and at the same 

 time observe the immediate operation of the iron on the pole to 

 which it was opposed, the experiment was transformed as follows. 

 A magnetic bar m, Fig. 13. (PI. XII.), being placed in a horizontal 

 position, with one of its extremities immediately under the sus- 

 pended cylinder x, and the number of degrees of attraction being 

 noted at a constant distance, a mass of iron n was approximated 

 toward the same extremity. In this case such portions of the 

 free magnetism of this extremity would become neutralized as 

 were proportional to the magnet's inductive effect, and this 

 would be evinced by the number of degrees which the index 

 declined. Thus we might come to determine experimentally all 

 the particular cases hitherto considered, a method of experi- 

 menting which, although not entirely free from objection, is still 

 useful, and sufficiently accurate to confirm the preceding results. 



34. The experiment being arranged as in Fig. 13, the effect of 

 the iron was, as in the former cases, directly proportional to the 

 power of the magnet m, and inversely proportional to the dis- 

 tance a b. In the following tables are given the results actually 

 obtained. The magnetic bars and iron employed being similar 

 to those before described (15). In these tables, D signifies the 

 distance a b between the iron and magnet, F the intensities of 

 the magnets, and /the force as expressed by the number of de- 

 grees which the index declined. The distance between the sus- 

 pended cylinder x and the magnet m being, in Table VI., six- 

 tenths of an inch, and in Table VII. eight-tenths of an inch ; 

 the constant distance a b, at which the variable magnetic forces 

 were applied in Table VII. being two-tenths of an inch. 



