First published in 1915 by the US Government Printing Office, an account of the inventions of Dr. Langley, a forgotten pioneer of the aeroplane. According to the Preface: "It is doubtful whether any person of the present generation will be able to appraise correctly the contributions thus far made to the development of the practical flying machine. The aeroplane as it stands to-day is the creation not of any one man, but rather of three generations of men. It was the invention of the nineteenth century; it will be the fruition, if not the perfection, of the twentieth century. During the long decades succeeding the time of Sir George Cayley, builder of aerial gliders and sagacious exponent of the laws of flight, continuous progress has been made in every department of theoretical and practical aviation—progress in accumulating the data of aeromechanics, in discovering the principles of this science, in improving the instruments of aerotechnic research, in devising the organs and perfecting the structural details of the present-day dynamic flying machine. From time to time numerous aerial craftsmen have flourished in the world's eye, only to pass presently into comparative obscurity, while others too neglected or too poorly appreciated in their own day subsequently have risen to high estimation and permanent honor in the minds of men."