I would like to point out a possible ambiguity in the paper by J. Dunham, in the October issue of the Journal. When considering the relative stresses in similar steel and aluminium alloy blades the author states that for blades “ doing the same duty ” the maximum stress in the steel blade is three times that in the aluminium type. This would seem to be true only if both blades are made to vibrate with the same tip amplitude, whereas the term “ doing the same duty” implies withstanding the same air loading, and consequently the steel and aluminium alloy blades would suffer different deflections.