8 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



plane as well as in a horizontal plane. This arrangement, 

 with its stand and graduated arc, furnishes the lecturer with 

 an instrument peculiarly adapted for the illustration of the 

 real influence of terrestrial magnetism upon magnetic bodies, 

 having free motion in all directions. 



Price, with graduated arc, $6.00. 

 " without " $3.00. 



Fig. 416. 



Fig. 417. 



Small Dipping Needle with Graduated Arc. (Fig. 416, 

 as above.) Small dipping needle, with brass graduated 

 quadrant, upon which the needle shows the dip. If this 

 small instrument be moved along a bar magnet, it illustrates 

 the relative situations and tendencies common to a needle 

 when acted upon by the influence of the earth's magnetism. 

 For when placed on the middle or equatorial part, the mu- 

 tual attractions of the north and south poles balance each 

 other, and cause the needle to stand exactly parallel to the 

 bar ; but as the needle is moved towards either extremity, 

 it will be inclined according to its distance from the mag- 

 netic poles. Price, $3.50 and $5.00. 



Dipping Needle with Graduated Ring. (Fig. 417, as 

 above.) Dipping needle with graduated brass ring, upon 

 which the needle indicates the inclination or dips due to ter- 

 restrial influence. When the apparatus is passed over a bar 

 magnet, a popular illustration is afforded of the action of the 

 earth's magnetism. Price, $6.00. 



