1884.] On a New Reflecting Galvanometer, Src, 295 



enters at a , and that by which it leaves the terminal by which the 

 current enters {3, fa, and that by which it leaves fa' , and so on. Then 

 the piece a and a a are in connexion, similarly a and «/, and so on for 

 all the pieces and terminals. The central piece p is connected to the 

 middle terminal of the instrument, the ring r to one of the other 

 terminals, and the piece s to the remaining terminal. 



The moveable or plug- connexions for joining the coils in series, or 

 in any other desired way, are now evident. For series, p is connected 

 by plug to a, a' to b, V to c, d to d, and d! to r. The current thus 

 enters by the middle terminal, passes round all the coils in the proper 

 direction and emerges by the terminal connected with r, and vice versa 

 for the reverse deflection. When the instrument is thus joined, the 

 piece s is generally connected by a plug with r, so that the two side 

 terminals of the galvanometer form one common electrode of the 

 instrument. A spare terminal- screw is thus available for one electrode 

 of a shunt-box, or for any other purpose. If it is desired to join the 

 pair of coils <z, (3 on one side in multiple arc, and in the same way 

 7 and 8 on the other side, and to connect these two pairs in series 

 a and b are connected together and to p by plugs, then a', b', c, d 

 together, and finally c' and d' together and to r or s. 



To join all the coils in multiple arc a, b, c, d are joined to p by 

 plugs, and similarly a', b', c', d' to r or s. 



If it is desired to use the instrument as a differential galvanometer 

 a may be joined to r, a' to b, and b' to p : again s joined to d' (the 

 divisions between s and r being unplugged), d to c! , and c to p. A 

 current then may be supposed to pass from one side terminal through 

 the coils a, /3, tending to turn the needle system in one direction, and 

 at the same time a current from the other side terminal of the instru- 

 ment through the coils $, 7, tending to turn the needle system in the 

 opposite direction, the two currents meeting in the middle terminal. 



This distributing plate can be joined so as to effect any other 

 desired arrangement ; and the same general plan of plate is applicable 

 to any galvanometer with multiple coils, or with coils wound in 

 sections. 



Lastly, we desire to propose one or two modifications of the instru- 

 ments described above. Instead of a set of four coils with hollow 

 cores and horseshoe needles as described, eight coils might be used — 

 one set of four arranged in rectangular order in a vertical plane 

 facing a second set of four similar coils in a parallel plane at a small 

 distance from the first. Two straight needles of thin steel wire con- 

 nected together as rigidly as possible by very light bars of aluminium,, 

 are so chosen as to length and so arranged that they hang from a 

 single silk fibre with their lengths vertical and a magnetic pole as 

 nearly as may be in the line joining the centres of each mutually 

 opposite pair of coils. A magnet giving a differential field at the 



