To determine the true dependence of flame velocity on pressure it is necessary to make a large number of measurements, because the velocity is not exactly constant within the stability region (see Wolfhard1). To make comparable measurements it is especially necessary to increase the burner diameter as the pressure is reduced, so that the diameter is inversely proportional to pressure. This was done for our measurements, but not for the older results referred to by Linnett and Wheatley. We do not deny that for the acetylene/air flame the flame velocity tends to increase slightly as the pressure is reduced ; but at still lower pressure the velocity decreases again, and the effect is probably due to the nitrogen. For flames in which the nitrogen of the air is replaced by argon, we have not observed any measurable change of velocity with pressure. We would emphasize that our results, especially for oxy-acetylene flames, are based on a very large number of measurements with various burner diameters and cover a big range of pressure (from 1 atm. to less than 0·01 atm.).