A different type of electrical anemometer is worthy of mention: the ionization anemometer of Lovelock and Wasilewska. It consisted essentially of a spherical openwork cage with a small spherical electrode at the centre coated with polonium which emitted a-particles and so ionized the air in its vicinity. The central sphere was connected to a 120V electrical source, and the cage was earthed. Thus the jons were caused to flow between sphere and cage and anelectric current was established, which could be measured. When the instrument was exposed to an airstream, the ion flow was disturbed and current changes occurred in terms of which the anemometer was calibrated. Its calibration was the same whatever the wind direction, and it was said to be able to measure velocities of less than 0.05 m/sec.

有一种不同类型的电风速计值得一提，这就是Lovelock公司和Wasilewska公司出品的电离速度计。它基本上由一个球形网罩和一个位于中心部分的小型球状电极构成。球状电极上镀有金属钋，钋发射出a粒子，因此使其附近的空气发生离解。中心球极与120伏的电源相连，外罩接地。这样，就使离子在中心球和外罩之间流动，从而形成一个电流。这一电流的大小可以加以测定。当把这种电离速度计置于气流中时，里边的离子流就会受到扰动，从而使电流发生变化。根据这种电流变化事先对这种速度计进行校测。其校测结果不管在什么风向下都一样，而且，据说能够用它来测量低于0.05米/秒的速度。

Another physical principle that has been used to measure fluid velocity is the effect of the motion on the velocity of acoustic-wave propagation, and flowrate in a pipe or duct has also been deduced from the displacement of an acoustic beam transverse to the flow. Although not used extensively, these methods are discussed briefly in Chapter XI. An account is also given in that Chapter of the measurement of flow velocity by observation of the Doppler frequency-shift of light reflected from minute solid particles (e. g. dust) moving with the fluid. This method has been made possible by the high-intensity narrow-beatm illumination of lasers; it has received a great deal of attention during the past decade, and is still being developed.

另一种已经用来测定流体速度的物理学原理是利用运动对于声波传播速度的影响。利用速一原理，也已从声波波束相对气流的横向位移推导出管道中的流量。虽然这些方法应用并不广泛，但还是在第11章中进行了简要的讨论。该章中还叙述了通过观测从随流体移动的固体微粒（即尘埃）上反射光的多普勒频移效应来测量流体速度的方法。利用激光提供的高强度窄波束照明，已使这种方法成为可能。这种方法在过去10年中受到了极大的注意，而且，现在人们仍在加以研究。

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