Tractor Principles, by Roger B. Whitman 67569 [Author: Roger B. Whitman] [Link: https://www.gutenberg.org/6/7/5/6/67569] [Files: 67569-0.txt; 67569-h.htm] Thanks to deaurider and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive) Regards, Al