To coax the nylon to twist in response to minute changes in the ambient field, you need to affix a powerful magnet to the fiber. Because a large and massive magnet responds only sluggishly, the ideal attractor would possess a powerful field and yet be extremely lightweight. Such magnetic miracles exist; they are called rare- earth magnets because they contain rare-earth elements, such as samarium. These marvels are tiny and yet harbor at their surface magnetic fields that are 10,000 times stronger than the earth's. Best of all, you can pick up a pair of them at any Radio Shack for less than $2 (part number 64-1895).
Deposit a thin smear of silicone cement on one rare-earth magnet and sandwich the filament between the two of them. Make sure that they overlap each other completely and are perfectly centered on the fiber as the glue hardens.
Baker fashioned the reflector from a small vanity mirror. With a glass cutter, he cut 1.5-millimeter-square chips, which he cemented together, back to back, centered on the fiber, just above and in contact with the rare-earth magnets. The mirror and magnets will then rotate as a well-balanced unit. Baker notes that the instrument will work better if you use the reflective surface on the back of the mirror to reflect light, which avoids the possibility that passage through the glass will distort the beam. To remove the lacquer that covers the reflective coating, use a Q-Tip to rub a little methyl ethyl ketone (MEK) on the back surface. If you would rather not work with a potentially toxic chemical, then install the mirrors in the usual way, with light passing through the glass.
Baker next glues a solid-copper penny (one minted before 1982, when the purity of the metal was still high) to the glass, just behind the magnets. When the magnets move, they induce electrical eddy currents in the copper that in turn produce their own magnetic fields, which oppose the motion of the magnets. Baker's clever trick quickly damps unwanted oscillations, making the magnetometer much easier to read.
Next, encase the sensor by gluing the second glass wall with its spacers on top of the first and then seal off the sides with black electrical tape to protect your magnetometer from pesky air currents. Mount the entire assembly vertically to a smooth flat base. Your sensor is now an accurate compass. As you walk around, the magnets should align to magnetic north and display little oscillation.
Because the earth's relatively large field absolutely overwhelms the coveted magnetic micropulsations, you must first null the instrument before it will register signals from the ionosphere. Baker's procedure for doing so requires another trip to Radio Shack to acquire four doughnut-shaped magnets (part number 64-1888). Attach them side by side to a small piece of glass or wood using silicone cement. (Note that you'll need to use small clamps to hold them in place against their mutual magnetic repulsion until the glue sets.) Turn the array of doughnut magnets upright and cement it to a freestanding base so that the center of the assembly aligns with the rare-earth magnets in the sensor.
As the nulling magnets are brought close to the magnetometer (approximately 30 centimeters), the sensor will begin to wobble and then rotate quite freely when the combined forces of the earth's magnetic field and those of the doughnut magnets almost cancel each other out. The period of the oscillations should lengthen to a second or more when all the forces are nearly balanced. In this configuration the magnetometer will be the most sensitive.