Demonstration Compass Science at Home Double-concave glass lens at 3-inch

Double-concave glass lens at 3-inch diameter and 200mm diverging focal length

An 18mm pole gap on this 37 x 13 x 10mm Alnico U-shape concentrates field strongly enough to bend filings into clear field lines

with both 4mm stackable sockets and screw terminals so leads wire in without an adapter to either bench standard

the standard configuration for keeping the field intact between classroom magnetism sessions

Demonstration Compass Science at Home Double-concave glass lens at 3-inchFive inch demonstration compass with a 4 inch magnetic needle and a printed compass map, sized so the needle stays readable from the back of the room.