The Magnetised Hairpin: Proving the Steel With a Compass

"Hair-pins are commonly made of iron or soft metal; but the better grade of these articles are made of steel. Unscrupulous dealers oftentimes sell the iron and soft-metal hair-pins for those made of steel, thus defrauding their customers". "The object of our improvement is to produce steel hair-pins which may be easily distinguished from those of inferior quality. To this end our improvement consists in a new article of manufacture--namely, a magnetized steel hair-pin." The ends are left bare as magnetic poles, and "A hair-pin embodying our improvement can be tested as to being magnetic by its ability to attract another".

Magnetise a hairpin, an iron nail and a straightened paper clip as in the program, the same number of strokes each. Test each one with the compass at 2, 4 and 8 cm, and count how many paper clips each will lift. Tap each ten times on the table and test again, then leave them a day and test again. Write down which kept its magnetism. Compare the fall-off with distance against the notebook.

**Charles A. Hussey** and **William H. Lyman** of New York filed US 255,292 on 4 February 1882; it is dated 21 March 1882. **Honest limits.** The patent says "steel is the only metal which will retain magnetism". That is not so: cobalt, nickel and some of their alloys also do, and soft iron keeps a little. The test shows a pin is not soft iron, not that it is good steel. The dipole formula is only a rough guide closer than the pin's own length, which is where the 1 and 2 cm rows sit. The earth's field and the magnetisations in the notebook are examples.