OF EI-ECTR0-DY.\AM1C FORCES. 495 



h h and h'h' rotates horizontally, and is furnished with a torsion- 

 circle and an index, as is distinctly seen in figs. 6 and 7 at A A'. 



Figs. 6 and 7 are not sectional, and fig. 6 belongs to fig. 2. 

 Fig. 7 exhibits the roller B with the prong and the screw e e' of 

 fig. 5 more distinctly; ii here represent two screws, to fix the 

 roller B on moving the instrument, without which precaution 

 the bifilar threads would be easily injured. 



We now pass to fig. 8, which exhibits in a vertical section the 

 lower part of the insti'ument, with the multiplier and the pede- 

 stal, which is constructed of serpentine. In it we first recognise 

 fig. 2, suspended by the bifilar metallic wires o and o', also as 

 seen on a vertical section. The letters m m exhibit a section of 

 the multiplier, wound round a brass drum furnished with wooden 

 sides, in the interior of which the vibrating cylinder R is placed. 

 These wooden sides support the tubes, within which the bifilar 

 threads descend ; the two scales for the indexarealsofixedtothem. 



Fig. 10, a view of the instrument as seen from above, exhibits 

 more accurately the scale and the metallic plates, to which the 

 tube is fastened. The sides of this multiplier are in connexion 

 with a strip of copper, which by means of two cap-screws can 

 be connected with the upper part n n of the foot of serpentine. 

 This portion, n n, with its cone i i, is capable of rotation in the 

 lower part of the serpentine foot, and by means of the metallic bolt 

 r is kept in connexion with it by the screw x. Since, as shown in 

 fig. 8, both the speculum and the counterpoise project towards 

 the wooden sides of the multiplier, the whole is protected from 

 the influence of a current of air by a cylindrical wooden cover, 

 which is fixed to the upper corners of the wooden sides of the 

 multiplier. In the direction of the speculum to the counter- 

 poise, however, this cylindrical cover is flattened, so as to allows 

 of a free view through the cavity of the multiplier. The flat 

 side of the cover next the speculum can be opened or closed at 

 pleasure by a wooden plate, w-hich however, to enable us to use 

 the mirror, is furnished with a flat parallel glass, S. The whole 

 of the other flat side of the cover, which is turned towards the 

 counterpoise, may be closed or opened by a glass plate. Thus 

 the vibrating reel, when the sides of the cover are closed, can 

 still be seen, and its free oscillation in the cavity of the multiplier 

 be observed and regulated by means of the three screws in the 

 serpentine pedestal. Moreover, from above downwards, above 

 the graduation, the cover is closed by two glass plates, which are 

 moveable towards each other in metallic grooves, and excavated 



