The internal motjon of a fluid assumes one or other of two distinct forms; either the elements follow one another in a direct and simple manner, or else they wander about in erratic paths as they progress downstream. In the first kind of motion, called “ regular ” or “ streamline,” the components of the velocity at any selected point are either constant, or vary in a definite manner directly related to the boundary motions. In the second, known as “ turbulent,” these components continually change in an irregular way, which cannot apparently be connected with the regular boundary motions.

A regular air service between Amsterdam and Batavia has now been in existence for more than two years, a fact which to-day is generally known. The great and mutual interests which bind Netherland with its colonies—interests of a cultural, commercial and also of a governmental nature—have always placed in the foreground the necessity of bridging over as rapidly as possible the enormous distance separating both territories.

The high-speed internal combustion engine presents many problems arising from dynamic effects. Amongst these is the phenomenon known as “ surging ” in the helical springs used for the operation of the valves.

If a helical spring is held at both ends, any disturbance in the spring passes up and down as a wave, being reflected at each end in turn. This to and fro movement continues until it is damped out by friction and air resistance. With most springs the speed of propagation of the disturbance is considerable and only a confused flutter of the coils is apparent to an observer. A disturbance of this type is caused by any movement of the end of the spring. The more abrupt the movement of the end, the more pronounced will the disturbance be. An instance of the type of movement producing a pronounced surge is that due to impact between the tappet and the valve when the valve commences to open.