| U2 = | T | { 1 + | κn − αn2 | } |
| ρ | T + (κn − αn2 l/a) |
(26)
for the vibration of helical nature like circular polarization.
Changing the sign of n for circular polarization in the opposite direction
| U′2 = | T | { 1 − | κn + αn2 | } |
| ρ | T − (κn + αn2 l/a) |
(27)
In this way a mechanical model is obtained of the action of a magnetized medium on polarized light, κ representing the equivalent of the magnetic field, while α may be ignored as insensible (J. Larmor, Proc. Lond. Math. Soc., 1890; Aether and Matter, Appendix E).
We notice that U2 in (26) can be positive, and the gyrostatic chain stable, even when T is negative, and the chain is supporting a thrust, provided κn is large enough, and the thrust does not exceed
(κn − an2) (1 + l/a);
(28)