During the past year the question as to the relative advantages of monoplane and biplane types has been brought very much to the fore owing to the unfortunate accidents that have occurred—the accidents in this country being all on the monoplane type of machine. In the present paper a comparison has been made of the stresses set up in the various parts of the two types, so that conclusions might be drawn as to the limits, if any, between which each type was most suitable. A further note is included giving a short comparison as to their respective aerodynamical qualities, so that the whole survey might be as complete as'possible.