1890 photo of the 152-foot high tower that was built in Greene, Indiana during the 39th parallel survey, which resulted in the first transcontinental arc of triangulation in the United States.

Survey towers allowed surveyors to obtain a clear line of sight over obstacles such as tall trees or across far distances. This is an 1890 photo of the 152-foot high tower that was built in Greene, Indiana, during the 39th parallel survey, which resulted in the first transcontinental arc of triangulation in the United States.