INDUSTRIAL PROGRESS DURING THE YEAR 1875. lxxiii 



iments of the author's have confirmed this fact. The ex- 

 planation of it he finds either in the electric current thus 

 generated in the boiler, the zinc being positive and the iron 

 negative, or more probably in the hydrogen continually set 

 free in minute quantity on the iron surface, thus preventing 

 the adherence of scale. (The author does not seem to be 

 aware that this same device is not new, having been employ- 

 ed for this purpose for many years in the United States.) 



Ducretet has noticed a remarkable property of aluminum 

 when conveying a current. If in a voltameter one of the 

 electrodes be aluminum, the other being of platinum, the for- 

 mer being negative, water is decomposed, hydrogen is set 

 free at the aluminum surface, and oxygen at the platinum, 

 the current passing freely. But if the aluminum electrode 

 be made positive, no action takes place, and no current, or a 

 very feeble one, passes. In the first case an electric bell in 

 the circuit rings violently, in the second not at all. It is 

 proposed to call a voltameter thus constructed a rheotome. 

 It is doubtless capable of many useful applications. 



Wilson has communicated a paper to the London Physical 

 Society on a method of measuring electrical resistance in liq- 

 uids, in which polarization of the electrodes is entirely avoid- 

 ed. A long, narrow trough is filled with the liquid to be 

 measured, and a porous cell filled with sulphate of zinc solu- 

 tion is placed at one end, and a similar one containing copper 

 sulphate at the other. In the first of these cells a plate of 

 zinc is placed, and in the second one of copper. The ex- 

 ternal circuit is completed through a resistance coil and gal- 

 vanometer. A suitable deflection is obtained at the start, 

 and then one of the porous cells is moved toward the other. 

 The deflection is of course increased, and resistance is intro- 

 duced to bring it back to that originally obtained. This in- 

 troduced resistance is evidently equal to that of the column 

 of liquid taken out of the circuit. 



Foster has given graphical solutions of a number of simple 

 electrical problems. He prefers the method in which the or- 

 t dinates represent electro-motive forces and the abscissas re- 

 sistances, and has devised a simple instrument which he calls 

 a galvanometric sliding-rule, by means of which many prob- 

 lems of this sort may be rapidly and accurately solved. 



Amory has published a brief note on the great facility with 



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