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XII. New Instrument for continuously recording the Strength 

 and Direction of a Varying Electric Current. By R. Shida, 

 M.E., Professor of Natural Philosophy in the Imperial 

 College of Engineering, Tokio, Japan. 



[Plates II. & III.] 



To Sir William Thomson, P.P. S. } LL.D., Sfc. 



Deae Sie William; 



I ENCLOSE herewith a paper which I have just drawn up 

 and which is a description of a new instrument I have 

 devised and constructed for continuously recording the strength 

 and direction of a varying electric current. My chief aim in 

 designing such an instrument was to use it for making obser- 

 vations of both regular and irregular variations of earth- 

 currents which are present in the telegraph-wires of this 

 country, just as they are present in the telegraph-wires of any 

 other country. The importance of carrying on careful ob- 

 servations of earth-currents has been felt more and more since 

 you showed it before the Society of Telegraph Engineers and 

 Electricians, about eleven years ago, in your presidential 

 address. Indeed, so great an importance is now attached to 

 such observations, that it was one of the main subjects discussed 

 by the International Electric Congress which met at Paris last 

 year. Now, since both regular and irregular earth-currents are 

 so variable, that their strength and direction change, not only 

 from day to day, but from hour to hour, or from minute to 

 minute, or even from second to second, observations will be of 

 very little value unless they are continuously made; hence the 

 importance of a method of continuously registering the strength 

 and direction of varying electric currents. The photographic 

 method, such as is used in the Kew Observatory, is, of course, 

 very satisfactory and accurate. But this method, besides 

 requiring an elaborate arrangement of several pieces of appa- 

 ratus, has a serious disadvantage, namely, that the observations 

 must be made in a dark room. I have therefore felt for a 

 long time the want of a method which, though not so accurate 

 as the photographic method, is simple and convenient. It 

 was thus that I was led to devise the apparatus described in 

 the accompanying paper. 



As will be seen from the description given in the paper, the 

 galvanometer-part of the apparatus is, in the main, the same 

 as that of the more recent one of your Siphon Recorders ; 

 that is to say, a coil containing a great number of turns of 

 fine wire is suspended in a strong magnetic field produced by 



