It may be that, as forecasted by the prophet Wells, the flapping-wing machine will yet come to its own and compete with the aeroplane in efficiency. Against this, however, are the practical advantages of the rotary mechanism of the aeroplane propeller as compared with the movement of a bird’s wing, which, according to Marey, moves in a figure of eight. The force derived from a propeller is of necessity continual, while it is equally obvious that that derived from a flapping movement is intermittent, and, in the recovery of a wing after completion of one stroke for the next, there is necessarily a certain cessation, if not loss, of power. The matter of experiment along any lines in connection with aviation is primarily one of hard cash. Throughout the whole history of flight up to the outbreak of the European war development has been handicapped on the score of finance, and, since the arrival of the aeroplane, both ornithopter and helicopter schools have been handicapped by this consideration. Thus serious study of the efficiency of wings in imitation of those of the living bird has not been carried to a point that might win success for this method of propulsion. Even Wilbur Wright studied this subject and propounded certain theories, while a later and possibly more scientific student, F. W. Lanchester, has also contributed empirical conclusions. Another and earlier student was Lawrence Hargrave, who made a wing-propelled model which achieved successful flight, and in 1885 was exhibited before the Royal Society of New South Wales. Hargrave called the principle on which his propeller worked that of a ‘Trochoided plane’; it was, in effect, similar to the feathering of an oar. Hargrave, to diverge for a brief while from the machine to the man, was one who, although he achieved nothing worthy of special remark, contributed a great deal of painstaking work to the science of flight. He made a series of experiments with man-lifting kites in addition to making a study of flapping-wing flight. It cannot be said that he set forth any new principle; his work was mainly imitative, but at the same time by developing ideas originated in great measure by others he helped toward the solution of the problem. Attempts at flight on the helicopter principle consist in the work of De la Landelle and others already mentioned. The possibility of flight by this method is modified by a very definite disadvantage of which lovers of the helicopter seem to take little account. It is always claimed for a machine of this type that it possesses great advantages both in rising and in landing, since, if it were effective, it would obviously be able to rise from and alight on any ground capable of containing its own bulk; a further advantage claimed is that the helicopter would be able to remain stationary in the air, maintaining itself in any position by the vertical lift of its propeller.