46 H. A. Rowland and L. Bell — Explanation of the 



rial on which the chemical action could take place are governed 

 by the general law of magnetic attraction and are held in place 

 against chemical energy precisely as they would be held against 

 purely mechanical force. To sum up : 



When the magnetic metals are exposed to chemical action 

 in a magnetic field such action is decreased or arrested at any 

 points where the rate of variation of the square of the mag- 

 netic force tends toward a maximum. 



It is quite clear that the above law expresses the facts thus 

 far obtained, and while in any given case the action of the 

 magnet is often complicated by subsidiary effects due to cur- 

 rents or by-products, the mechanical laws of motion of parti- 

 cles in a magnetic field hold here as elsewhere and cause the 

 chemical action to be confined to those points where the mag- 

 netic force is comparatively uniform. 



The effect of currents set up in the liquid during the action 

 of the magnet cannot be disregarded especially in such experi- 

 ments as those of Nichols (this Journal, xxxi, 272, 1886) where 

 the material acted on was powdered iron and the disturbances 

 produced by the magnet would be particularly potent. The 

 recent experiments of Colardeau (Journal de Physique, March, 

 1887) while perhaps neglecting the question of direct protec- ' 

 tion of the poles, have furnished additional proof of the 

 purely mechanical action of the magnet by reproducing some 

 of the characteristic phenomena where chemical action was 

 eliminated and the only forces acting were the ordinary mag- 

 netic attractions. 



An attempt was made to reverse the magnetic action, i. e. to 

 deposit iron in a magnetic field and increase its deposition 

 where there was a sharp pole immediately behind the plate on 

 which the iron was being deposited. This attempt failed. 

 The action was very irregular and the results not decisive. 

 The question of stirring effect was also examined. Usually 

 stirring the liquid about one pole increased the action on that 

 pole, but sometimes produced little effect or even decreased it. 

 This however is in entire agreement with the irregular action 

 sometimes observed in the case of the after-effect in the orig- 

 inal experiments. 



An excellent method of experiment is to imbed an iron 

 point in wax leaving the minute point exposed : imbed a fiat 

 plate also in wax and expose a point in its center. Place the 

 point opposite to the plate, but not too near and place in the 

 liquid between the poles of a magnet and attach to the galva- 

 nometer as before. 



There is a wide field for experiment in the direction indi- 

 cated above, for it is certainly very curious that the effect 

 varies so much. If hydrogen were as magnetic as iron, of 



