Strength and Direction of a Varying Electric Current. 97 



permanent * magnets. There is, however, one point in the 

 apparatus which is quite new, at least quite new to my know- 

 ledge : that is, that the advantage is taken of a singular pro- 

 perty of matter, " surface-tension of liquids." We know very 

 well that a mercury-drop is often used for the purpose of 

 making and breaking an electric circuit. But nobody has 

 used a water-drop or an acidulated-water drop for the same 

 purpose. The advantage of a water-drop over a mercury- 

 drop, when employed for opening and closing an electric 

 circuit, is that the former offers a far smaller resistance than 

 the latter to the moving body which comes in contact with it. 

 Now, in the instrument I am speaking of, a water-drop or, 

 what is equivalent to it, a thin column of water drawn up 

 between two narrow plates partly immersed in water, is used 

 for the purpose of making and breaking the circuit, as will 

 be seen from the description given in the paper. 



For the further details of the apparatus I ask you to be 

 good enough to refer to the paper itself. 



The Instrument, I might mention, may of course be used 

 as a " coulombmeter," because since in the paper ribbon, on 

 which a record is obtained, the abscissas represent times and 

 the ordinates represent currents, the area included by (the 

 abscissa) the line of no current, and the ordinates correspond- 

 ing to any two times and the curve of current, represents the 

 quantity of electricity passed through the apparatus during 



the interval between the two times. 



* * * * 



R. Shida. 



One of the principal subjects discussed by the International 

 Electric Congress held in Paris in 1884, was that of Earth- 

 currents ; and the result of the Congress as regards earth- 

 currents was "that the Conference expresses the wish tbat 

 observations of earth-currents be pursued in all countries."" 

 This resolution, together with the others, has been communi- 

 cated to the various Governments ; and our Government 

 having conformed to the wish of the Conference, it was decided 

 that the observations of earth- currents be made by the Tele- 

 graph Department, in which I am a chief engineer. It thus 

 devolved on me to take the subject up. A little consideration, 

 suggested by the results of preliminary observations I have 

 made of earth-currents, revealed to me that in order to carry 

 out systematic observations of earth-currents, which, from 

 time to time, vary in strength and direction, it is almost 

 necessary, or at least extremely convenient, to have at our 

 disposal a simple instrument which will continuously record 

 Phil. Mag. S. 5. Vol. 22. No. 135. August 1886. H 



