Question: when was the idea of the atom first introduced
[{'answer': '19th century', 'provenance': [{'wikipedia_id': '902', 'title': 'Atom', 'start_paragraph_id': 38, 'start_character': 624, 'end_paragraph_id': 38, 'end_character': 636, 'bleu_score': 1.0, 'section': 'Section::::Structure.:Subatomic particles.\n'}]}]