Sentence:  I have written a second book, "Vrilology", which explores the historic background of the Life Force, which we refer to as <WSD>Vril</WSD>, and another simple book explaining just what <WSD>Vril</WSD> is and how it can help people improve their lives, filling them with happiness, joy and prosperity. 
Meaning of the word marked with <WSD> tags:  A controllable form of energy.