298 POGGENDORFF ON THE PHENOMENA OF 



netism of closed electro-magnets, it is clear that they will stand 

 in a definite relation to the lifting power, and the question now 

 is, in what relation ? 



Before making the experiments above-mentioned, the author 

 believed that the lifting power, like the actio in distans, would 

 be proportional to the square of the strength of the current b; a 

 glance however at the numbers obtained, renders this conjecture 

 in the highest degree improbable. 



To obtain further information upon this point, new experi- 

 ments were made, in which, with the same horse-shoe magnet, 

 and with currents of different strength, w^ere measured both the 

 total and the permanent force, as also the current of induction b. 



Different circumstances prevented these measurements from 

 being made with all the exactitude that might be wished, but 

 they show, nevertheless, in the most decided manner, that the 

 temporary lifting power, that is, the total minus the permanent, 

 is far from being proportional to the square of the inducted cur- 

 rent b, but on the contrary is nearly proportional to the current 

 itself, or in other words, to the simple force of the magnet. 



Even considering the incompleteness of his measurements, and 

 the great difficulty, notwithstanding all precautions, w^hich the 

 determination of the lifting power will always present, the author 

 would not be disinclined to regard even now the simple propor- 

 tionality of the lifting power, to the magnetic intensity, as the 

 true expression of the state of the case, did he not consider it 

 more prudent to defer his definite opinion, until by a repetition 

 of the experiments with more perfect instruments, the certainty 

 of the numerical results is more surely established than at 

 present. 



The author takes this opportunity of observing, that should 

 future observations confirm his proposition, still the latter would 

 not be quite the same as the results of J. Tyndall*, "that the 

 mutual attraction of an electro-magnet and a sphere of soft iron, 



* I take this opportunity of introducing an ingenious and probably well- 

 grounded objection urged by M. Dub against the universality of this result. 

 Where magnet and submagnet are separated by a short interval, the attrac- 

 tion is proportional to the square of the strength of the magnet. M. Dub 

 argues thus : — ** If the increase in the case of contact be simply proportional 

 to the magnetic strength, and at a distance to the square of the strength, we 



