Battaillonskommandeur im Badischen Fussartillerie Regiment No. 14; in collaboration with O. Chanute and others. Translated by W. Mansergh Varley, B.A., D.Sc., Ph.D., and published by Whittaker & Co. This work does not, however, confine itself altogether to flying machines, but has a great deal of information which is of little or no value to the builder of true flying machines; moreover, it is not simple enough to be readily understood by the majority of experimenters. In some other works which I have recently examined, I find a confusing mass of the most intricate mathematical calculations, abounding in an almost infinite number of characters, and extending over hundreds of pages, but on a close examination of some of the deductions arrived at, I find that a good many of the mathematical equations are based on a mistaken hypothesis, and the results arrived at are very wide of the truth. I have shown several diagrams which will explain what I mean. What is required by experimenters in flying machines--and there will soon be a great number of them--is a treatise which they can understand, and which requires no more delicate instruments than a carpenter’s 2-foot rule and a grocer’s scales. The calculations relating to the lift, drift, and the skin friction of an aeroplane are extremely simple, and it is quite possible to so place this matter that it can be understood by anyone who has the least smattering of mathematical knowledge. Mathematics of the higher order expressed in elaborate formulæ do very well in communications between college professors--that is, if they happen to be agreed. When, however, these calculations are so intricate as to require a clever mathematician a whole day to study out the meaning of a single page, and if when the riddle is solved, we find that these calculations are based on a fallacy, and the results in conflict with facts, it becomes quite evident to the actual experimenter that they are of little value. For many years, Newton’s law was implicitly relied upon. Chanute, after going over my experimental work, wrote that Newton’s law was out as 20 is to 1--that is, that an aeroplane would lift twenty times as much in practice as could be shown by the use of Newton’s formula. Some recent experiments, which I have made myself, at extremely high velocities and at a very low angle, seem to demonstrate that the error is nearer 100 to 1 than 20 to 1. It will, therefore, be seen how little this subject was understood until quite recently, and even now the mathematicians who write books and use such an immense amount of formulæ, do not agree by any means, as will be witnessed by the mass of conflicting controversy which has been appearing in _Engineering_ during the last four months. When an aeroplane placed at a working angle of, say, 1 in 10 is driven through the air at a high velocity, it, of course, pushes the air beneath it downwards at one-tenth part of its