Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . 266 STADI A TA CH YME TR V. if on the top margin, multiply the correction by o, i ; if onthe bottom margin, multiply the correction by ; and if onthe right-hand margin, multiply the correction by lo. 30 40 60 TO SO 90 100. Fig. 8o.—Diagram for Reducing Inclined Stadia Distances to Hori-zontal. III. Effects of Refraction on Stadia Measurements.—Experiments by Mr. J. L. Van Ornum in his stadia-workshowed that the disturbing effect of refraction increa
Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . 266 STADI A TA CH YME TR V. if on the top margin, multiply the correction by o, i ; if onthe bottom margin, multiply the correction by ; and if onthe right-hand margin, multiply the correction by lo. 30 40 60 TO SO 90 100. Fig. 8o.—Diagram for Reducing Inclined Stadia Distances to Hori-zontal. III. Effects of Refraction on Stadia Measurements.—Experiments by Mr. J. L. Van Ornum in his stadia-workshowed that the disturbing effect of refraction increasedenormously toward the ground, even if the foot of the rodwere unobstructed. When no error in observation is madeand the refraction remains constant from the time of the EFFECTS OF REFRACTION ON STADIA. 26j foresight to the time of the backsight, the elevation of anypoint can be computed by the formula H = H-\- \{h + in -\-n- h\ . . (13) in which 77= elevation of known station; // = height of instrument at that station;m = total vertical component of the foresight;77 = elevation of the unknown station;// = height of the instrument at the unknown station; andn = the total vertical component of the backsight. The average error of closing in Mr. Van Ornums workbefore the adoption of this formula was more than halfgreater than after its use. The effect of
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