the nebulae are rapidly dispersing. The velocities are direct evidence of a hustle which (according to the usual ideas of the rate of evolutionary change) is out of keeping with the character of our staid old universe. Thus the only way of avoiding a great upset of ideas would be to explain away these radial velocities as spurious. What is actually observed is a shifting of the spectrum of the nebula towards the red. Such a shift is commonly caused by the Doppler effect of a receding velocity, in