How does it work? This question has been put to me so often by persons young and old that I have at last decided to answer it in such a manner that a much larger public than that with which I have personal acquaintance may be able to satisfy themselves as to the principles underlying many of the mechanisms met with in everyday life. (see http://www.gutenberg.org/files/28553/28553-h/28553-h.htm for illustrations)
