ELECTRO-MAGNETIC INSTRUMENTS. 



19 



nometer, with astatic needle, which will be readily under 

 stood by a reference to those already described. 



Price, $6.00 



Improved Galvanometer, with Astatic 

 Needle. (Fig. 435.) In this cut is repre- 

 sented an instrument similar to the last, 

 with delicate and elegant adjustments, form- 

 ing a galvanic multiplier, the sensibility of 

 which may be illustrated by making with it 

 the following experiment : Twist a piece of 

 iron or zinc wire round one of the binding 

 screws, connected with one extremity of the 

 coil ; place on the top of the other binding 

 screw a drop of spring water, into which 

 dip the other end of the wire, the needles 

 will immediately be moved by the weak 

 current thus set in motion. Price, $15.00. 



Fig. 435. 



Gold Leaf Galvanoscope.(Yig. 436.) ? 436 



The construction of this instrument 

 is similar to that of Bennet's electro- 

 meter, excepting that the leaf is single, 

 and there is added a forceps to retain 

 the lower end of the gold leaf, and 

 complete the galvanic circuit. The 

 slip of gold leaf, g, is suspended loose- 

 ly from the forceps, /, while the lower 

 end is laid hold of by another forceps 

 h y each forceps terminating in a cup, 

 the one, P, being above, and the other, 

 N", below, for establishing the commu- 

 nications by which the current is trans- 

 mitted through the gold leaf. The 

 whole is enclosed in a cylindrical glass 

 case, the middle of which is placed 

 between the poles of a strong horse- 

 shoe magnet, M, m, so that the gold 

 veaf may be nearly equidistant from them. When the 

 circuit is completed through the gold leaf, the latter will be 

 Attracted or repelled laterally by the poles of the magnet, 

 according as the current is ascending or descending ; the 



