Abstract
The instrument has been subjected to a series of three full-scale tests, the results of which are presented here in greater or less detail in chronological order corresponding to certain stages of development and knowledge of the sources of error. In each case a complete trigonometric figure with redundancies has been measured and subjected to analysis. The lines as measured have been corrected for slope due to the relative height of the stations, reduced to sea level, and corrections applied to bring them into an appropriate plane projection. It has been assumed that the ray path is optically straight and curvature corrections have been applied accordingly. In radio practice it is assumed that at ground level such waves travel in straight lines relative to an apparent earth's radius 4/3 times the actual radius, due to the normal vertical gradient of refractive index. If this value of radius is used in the curvature formula, the dip of the ray into a region of higher refractive index and its curvature is completely allowed for in normal atmospheric conditions. The corrections are quite small below 30 miles but increase rapidly at greater ranges.

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