ScientificAmerican1917-04-21.jpg Scientific American 1904-02-06ThumbnailsScientific American 1923-11Scientific American 1904-02-06ThumbnailsScientific American 1923-11Scientific American 1904-02-06ThumbnailsScientific American 1923-11Scientific American 1904-02-06ThumbnailsScientific American 1923-11Scientific American 1904-02-06ThumbnailsScientific American 1923-11
Plunging through an irrigating ditch with a continuous-tread tractor.