.....as a grass-hopper , due to a steam engine , at : http://en.wikipedia.org/wiki/File:Marine_grasshopper_engine.jpg (http://en.wikipedia.org/wiki/File:Marine_grasshopper_engine.jpg)
....or , as a self-moving mass , due to a continuous gravity unbalance , at :
http://www.geocities.ws/iacob_alex/Some_Drafts/text036.jpg (http://www.geocities.ws/iacob_alex/Some_Drafts/text036.jpg)
Al_ex