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No further practical advance appears to have been made in the design or construction of the reflecting telescopes for another 50 years until John Hadley ( best known as the inventor of the octant ) developed ways to make precision aspheric and parabolic speculum metal mirrors .
 John Hadley
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 John Hadley