3. The velocities of the Orion nebula, the Trifid nebula, the
Carina nebula, and of several other irregular nebulae, have
been measured with the spectroscope. These bodies seem to be
nearly at rest with reference to the stellar system. The helium
stars have the lowest-known stellar velocities, and the average
velocities of the stars are higher and higher as we pass from
the helium stars, through the hydrogen and solar stars, up to
the red stars. The average velocities of the brighter stars of
the different spectral classes, as determined with the D. O.
Mills spectrographs at Mount Hamilton and in Chile, are as in
the following table:
