16 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



Fig - 429 - which is fixed in a maho- 



gany base, and connected 

 with a cap at one end of 

 the base, by a wire on the 

 bottom. The coil is sup- 

 ported at the upper part by 

 a vertical arm, and termi- 

 ates in a cup with binding 

 screw, as also the one on 

 the base, for connecting 

 with the poles of the bat- 

 tery ; on transmitting a cur- 

 rent through the coil, polar- 

 ity and magnetic attraction 

 are produced, one side of the coil being north and the other 

 south. Price, $2.00. 



FSg-430. Apparatus for Oer- 



sted's Experiment. 

 (Fig. 430.) This con- 

 sists of a rectangular 

 frame of brass, support- 

 ing three cups with 

 binding screws, in such 

 a manner that a current 

 may be sent above a 

 needle suspended within 

 the frame, or below the needle, or in both directions, ac- 

 cording as the connexions are made ; the wires P and N 

 being insulated where they cross. A positive current pass- 

 ing horizontally over the needle, from north to south, has a 

 tendency to cause the north pole to move to the east ; con- 

 sequently, if another current be made to pass under the 

 wire, from south to north, the needle will be affected with 

 twice the force that a single wire would have exerted ; or, 

 what is the same thing, a continuous wire may b*e bent back 

 on itself, as in the figure, and this constitutes the simplest 

 form of the galvanometer. The current, passing in oppo- 

 site directions, above and below the needle, will conspire, 

 in both cases, to deflect it from its natural position, and in 

 the same direction, and to bring it into a position nearer to 

 right angles to the plane of the wires. Price, $3.00. 



