Sentence:  The general <WSD>theory</WSD> of resonance shifts is used to derive a general expression for the second moment **f of a polycrystalline paramagnetic sample and is specialized to **f . 
Meaning of the word marked with <WSD> tags:  a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena