Final answer:
The specific details of what Agatha and Sophie found hanging in midair inside the School Master's tower are not given in the provided excerpts, but the theme of magic in the texts suggests it could be an enchanted or unusual object.
Step-by-step explanation:
The inquiry about what Agatha and Sophie discovered suspended magically in midair within the School Master's tower isn't explicitly addressed in the provided text snippets. Nevertheless, the passages imply a recurring theme of magic and the unexpected. Instances include the abrupt emergence of various enchanted or mysterious items, such as the expansive white object ascending from the sage, the veiled presence of Lady Madeline of Usher, and the employment of hydrogen balls to counteract gravity in Sister Sara's air-car. In a magical context akin to these excerpts, encountering items like ancient scrolls, bewitched objects, or even an individual suspended mysteriously in midair would not be out of the ordinary.