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(31 Figure 149 gives an illustration of the relative appearance of the mirage under varying velocities and directions. In general, the shallower the waves of the mirage the faster the wind speed.
<41 The tme direction of the wind may be determined by traversing the telescope until the heat waves move straight up without lateral motion la boiling mirage I.
<51 A mirage is particularly valuable Id reading so-called "no value1' winds. If the mirage la boiling, the effective wind velocity is sero. If there is any lateral movement of the mirage at ranges of 300 to 900 meters it Is usually neoessary to maka a windage adjustment.
(6) Another effect of mirage la the light refraction caused by the uneven air densities.
Depending on atmospheric conditions, this refraction will cause a displacement of the target Image in the direction of the movement of the mirage. Thus, if a mirage is moving from left to right, the target will appear to be slightly to the right of Its actual location. Since the firer can only aim at the Image received by his eye, he will actually aim at a point which is offset slightly from the center of the target. This error will be small compared to the displacement of the bullet caused by the wind, but will have to be taken into account even on windless days since a boiling mirage may cause a vertical displacement of the target. Since the total effect of the visible mirage (effective wind plus target displacement) will vary considerably with atmospheric conditions and light intensity, it Is impossible to predict the amount of error produced at any given place and time. It is only through considerable experience in reading mirage that the firer will develop proficiency as a "wind doper.1*
4. tOJUNGMTH LATIRAL LIFT TO RIGHT
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