Michael Sharratt Galileo: Decisive Innovator xiii+247 1994 Blackwell Oxford 06311 7682 9 £19.99

Abstract

Red-shifts of some 600 extragalactic nebulae have been measured from spectra obtained at Mount Wilson (1928–1949) and at Palomar Mountain beginning in 1950. The dispersion used for most of the spectra ranged from 370 Å per mm to 490 Å per mm. Estimated probable errors are of the order of 35 km per sec.Greatest red-shift observed with the 100-inch is + 42,000 km per sec (Table 1). Largest red red-shift so far observed with the 200-inch is + 60,920 km per sec, the mean for three nebulae in Cl. 0855+ 0322. Photographic magnitudes for the nebulae observed in this cluster are 19 or fainter (Table 2). At that magnitude Hubble's law of red-shifts still appears to be linear, and red-shifts increase at the rate of about 530 km per sec per million parsecs.Red-shifts cannot be distinguished from Doppler shifts; they are constant throughout any given spectrum within the errors of measurement. The largest red-shifts observed with the 200-inch now approximate one-fifth the velocity of light. If red-shifts are velocities, then measurements of line displacements should be reduced by use of the relativistic Doppler equation, and true velocities would become noticeably smaller than the values c.dλ/λ.The observations have not appreciably changed the value of the Hubble constant. When final magnitudes are secured in the clusters from which red-shifts have been obtained, it should be possible to derive a more precise formulation of Hubble's law of the red-shifts.