4 KudoZ points awarded for this answer. Comment: "Thank you. On the basis of this answer, I found the terms "series aiding" and "series opposing" on several sites using Google, including the following definition: Series Aiding and Opposing Sources In many practical applications a circuit may contain more than one source of emf. Sources of emf that cause current to flow in the same direction are considered to be SERIES AIDING and the voltages are added. Sources of emf that would tend to force current in opposite directions are said to be SERIES OPPOSING, and the effective source voltage is the difference between the opposing voltages. When two opposing sources are inserted into a circuit current flow would be in a direction determined by the larger source. This is on one page of what looks like a very useful all-English technical dictionary site at http://www.tpub.com/home.htm Thanks also to others who answered."