org/licenses/by-sa/2.0CC BY-SA 2.0 Creative Commons Attribution-Share Alike 2.0 truetrue This image is a derivative work of the following images: Image:Heliograph (1)
September 2018 English US Forest Service lookout using a Colomb shutter type heliograph in 1912 at the end of a telephone line operator: Flickr described at URL:
https://creativecommons.org/licenses/by/2.0CC BY 2.0 Creative Commons Attribution 2.0 truetrue 1731 1447 431 745 3793 2675 Double-Tripod heliograph. US Signal Service Model