244 HENRY A. EOWLAND 



rent was sent through the magnet; i. e., only the latter part of the 

 previous phenomenon appeared under these circumstances. 



When the poles, instead of being placed in the field along the lines 

 of force, were held firmly perpendicular to them, the protective throw 

 disappeared completely, though as before there was a slight reverse 

 after-effect. 



Some of Professor Eemsen's experiments on the corrosion of a wire 

 in strong nitric acid were repeated with the same results as he obtained, 

 viz.: the wire was eaten away to the general dumb-bell form, though 

 the protected ends instead of being club-shaped were perceptibly hol- 

 lowed. When the wire thus exposed was filed to a sharp point the 

 extreme point was very perfectly protected, while there was a slight 

 tendency to hollow the sides of the cone, and the remainder of the 

 wire was as in the previous experiments. In both cases the bars were 

 steel and showed near the ends curious corrugations, the metal being 

 left here and there in sharp ridges and points. In one case the cylinder 

 was eaten away on sides and ends so that a ridge of almost knife-like 

 sharpness was left projecting from the periphery of the ends. 



These were the principal phenomena observed with nitric acid. 

 Since this acid is the only one which attacks iron freely in the cold, in 

 Prof. Eemsen's experiment, this was the one to which experiments were 

 in the main confined. With the present method, however, it was pos- 

 sible to trace the effect of the magnet whenever there was the slightest 

 action on the iron, and consequently a large number of substances, some 

 of which hardly produce any action, could be used with not a little facility. 



In thus extending the experiments some difficulties had to be 

 encountered. In many cases the action on the iron was so irregular 

 that it was only after numerous experiments under widely varying 

 conditions that the effect of the magnet could be definitely determined. 

 Frequently the direction of 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 remained always 

 unchanged, uniformly showing protection of the point so long as the 

 wires remained parallel to the lines of force. When, however, the 

 original action and the magnetic effect coincided in direction, the repe- 

 tition of the latter showed a decided tendency 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 magnet circuit 

 was broken as a violent throw in the reverse direction, showing that the 

 combination had been acting like a miniature storage batterv which 



