k = 0 Lorentz-Einstein
k = 1 Ritz.
Prof. de Sitter admits the validity of the criticisms. But he remarks that an upper value of k may be calculated from the observations of the double star β-Aurigae. For this star, the parallax π = ·014″, e = ·005, u₀ = 110 km/sec, T = 3·96,
Δ > 65 light-years,
k is < ·002.
For an experimental proof, see a paper by C. Majorana. Phil. Mag., Vol. 35, p. 163.
[M. N. S.]
Note 10.
Rest-density of Electricity.
If ρ is the volume density in a moving system then ρ√(1 - u²) is the corresponding quantity in the corresponding volume in the fixed system, that is, in the system at rest, and hence it is termed the rest-density of electricity.
[P. C. M.]