For several years the United States Coast and Geodetic Survey has carried on intermittently a series of experiments with color‐filters on first‐ and second‐order theodolites and first‐order levels in an attempt to improve the appearance of the object pointed upon by eliminating as far as possible the disturbances caused by heat‐radiation and scattering light. It is consistent with Huyghen's theory that the red and yellow filters are found to be the best for absorbing the disturbing lights of the short‐wave length, namely, those approaching the ultra‐violet part of