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A theory of electromagnetism , known as classical electromagnetism , was developed by various physicists during the period between 1820 and 1873 when it culminated in the publication of a treatise by James Clerk Maxwell , which unified the preceding developments into a single theory and discovered the electromagnetic nature of light .
 person: James Clerk Maxwell
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: James Clerk Maxwell 
Answer:
 person: James Clerk Maxwell