108 Messrs. Rowland and Bell o?i the 



original action would be reversed in the course of a series of 

 experiments without any apparent cause, but in such case the 

 direction of the effect due to the magnet always remained un- 

 changed, uniformly showing protection of the point so long as 

 the wires remained parallel to the lines of force. When, how- 

 ever, the original action and the magnetic effect coincided in 

 direction, the repetition of the latter showed a decided ten- 

 dency to increase the former. 



When using solutions of various salts more or less freely 

 precipitated by the iron, it frequently happened that the 

 normal protective throw was nearly or quite absent, but 

 showed itself when the magnetic circuit was broken as a violent 

 throw in the reverse direction, showing that the combination 

 had been acting like a miniature storage battery which 

 promptly discharged itself when the charging was discontinued 

 by breaking the current through the magnet. The gradual 

 reversal of the current some little time after exciting the 

 magnet was noted frequently in these cases, as before. 

 Owing to this peculiarity and their generally very irregular 

 action, the various salts were disagreeable substances to ex- 

 periment with, though as a rule they gave positive results. 



Unless the poles were kept clean experimenting became 

 difficult from the accumulation of decomposition products 

 about them and oxidation of their surfaces. A few experi- 

 ments showed how easily the original deflection could be 

 modified, nearly annulled, or even reversed in direction by 

 slight differences in the condition of the poles. These diffi- 

 culties of the method are, however, more than counterbalanced 

 by its rapidity and delicacy when proper precautions are 

 taken. 



Nearly thirty substances were tested in the manner previ- 

 ously described, but comparatively few of them gave very 

 decided effects with the magnet, though, as later experiments 

 have shown, the protective action is a general one. The 

 substances first tried were as follows. The table shows the 

 various acids and salts tried, and their effects as shown by the 

 original apparatus. 



Several things are worthy of note in this list. In the first 

 place those solutions of metallic salts which are precipitated 

 by iron all show distinct signs of protective action when the 

 current is passed through the magnet. Of the various acids 

 this is not generally true, only those showing the magnetic 

 effect which act on iron without the evolution of hydrogen, 

 and are powerful oxidizing agents. In general substances 

 which acted without the evolution of hydrogen gave an effect 

 with the magnet. 



