It may thus be seen that the two-stroke cycle type got as far as actual experiment in air work, and that with considerable success. So far, however, the greater reliability of the four-stroke cycle has rendered it practically the only aircraft engine, and the two-stroke has yet some way to travel before it becomes a formidable competitor, in spite of its admitted theoretical and questioned practical advantages. The attraction of the helicopter lies, probably, in the ease with which flight is demonstrated by means87 of models constructed on this principle, but one truism with regard to the principles of flight is that the problems change remarkably, and often unexpectedly, with the size of the machine constructed for experiment. Berriman, in a brief but very interesting manual entitled Principles of Flight, assumed that 鈥榯here is a significant dimension of which the effective area is an expression of the second power, while the weight became an expression of the third power. Then once again we have the two-thirds power law militating against the successful construction of large helicopters, on the ground that the essential weight increases disproportionately fast to the effective area. From a consideration of the structural features of propellers it is evident that this particular relationship does not apply in practice, but it seems reasonable that some such governing factor should exist as an explanation of the apparent failure of all full-sized machines that have been constructed. Among models there is nothing more strikingly successful than the toy helicopter, in which the essential weight is so small compared with the effective area.鈥? XX THE WAR PERIOD鈥擨I His youth, his engaging manners, frank address, and invariable gentleness to all who approached him, had won many friends, and the trial excited much interest. 超碰国产人人做人人爽 4 Then came the Word of God to Adam, and said to him, "O Adam, as you have shed your blood, so will I shed My own blood when I become flesh of your descendants; and as you died, O Adam, so also will I die. And as you built an altar, so also will I make for you an altar of the earth; and as you offered your blood on it, so also will I offer My blood on an altar on the earth. Charlotte鈥檚 鈥榣ines鈥?were many in number. Chapter XXVI J. S. Donovan.